Pines are known to mankind from the time immemorial. It offers both direct uses, as well as indirect uses specially soil conservation. Initially it was used mainly for fuel; their branches were used for festivals etc. However, now pine trees are used as a source of resin which on distillation yields gum rosin and turpentine oil. The genius pine species tapped for their oleoresin in different countries.
The present book has been published having in views the important uses of pines. The book contains manufacturing process of different products extracted from pines like oleoresin, rosin, turpentine derivatives, tall oil, resins and dimer acids etc.
This is the first book of its kind which is very useful for all from researchers to professionals.
Pinus
Introduction
The
genus Pinus L, comprising evergreen trees has been known to mankind
from time immemorial. Theophrastus (372-287 B.C.) in his early writings
made a reference to the morphology and reproduction of pines. Its
decorative value has been exploited in old Chinese paintings. Pine
incense used to be burnt in the religious ceremonies of the Mayas, the
Aztecs and the Romans.
The pines have been traced
back in geological history to the Jurassic period (150 million years)
though they reached their climax of distribution only in the Tertiary
(60 million years). By the lower Cretaceous (125 million years), two
distinct groups emerged, viz., (i) Haploxylon or soft pines and (ii)
Diploxylon or hard pines. The plants exhibit an exceptionally long
life. In the Inyo National Forests of California, USA, there is a tree
of Pinus aristata, which is more than 4600 years old, still producing
cones occasionally.
Pinus belongs to the family
Pinaceae or Abietaceae of the order Coniferales. The other genera
included in this family are Abies Mill., Cathaya Chun & Kuang,
Cedrus Link., Keteleeria Carr., Larix Mill., Picea A. Dietr.,
Pseudolarix Gord., Pseudotsuga Carr., and Tsuga Carr.
Some of the characteristic
features of the family are as follows: the plants are monecious, the
microsporophylls are spirally arranged with two abaxial sporangia per
sporophyll; female cones with numerous spirally arranged pairs of
scales (seed-scale-complex), viz. ovuliferous scales and the bract
scales, the former free from the latter or only slightly fused at the
base; ovules adaxial with their micropyles directed towards cone-axis;
and seeds generally winged.
Distribution
The genus has a cosmopolitan
distribution and is represented by about 105 species Jackson however,
mention c. 80 valid species. It is found mainly in the northern
hemisphere: northern Europe, northern and central America, Bahamas,
British Honduras, the subtropics of North Africa, the Canary Islands,
Afghanistan, Pakistan, India, Burma and the Philippines, crossing the
Equator in Indonesia. In the tropical countries like India, it is found
in the hills with subtropical or temperate climates, though some pines
are grown as ornamentals even at lower altitudes.
Distribution in India
In the Indian subcontinent
there are six species of Pinus of which four are distributed in the
Himalayas. They are P. roxburghii Sarg., P. wallichiana A.B. Jacks., P.
insularis Endl., and P. gerardiana Wall. ex Lamb. A few trees of P.
armandii Franch. occur in the North East Frontier Agency— NEFA P.
merkusii Jungh. & de Vriese grows on the hills of Burma. The
altitudinal range of these pines varies considerably.
Apart from indigenous species, some
exotic species also occur. These are listed below along with the areas
where they were successfully planted.
Morphology
In their general habit, young
pine trees are pyramidal with their horizontal branches disposed in
regular whorls. As the tree matures, this symmetry is lost and the
crown becomes rounded, flat, or even spreading. Under cultivation, when
planted close, the trees lose their branches and thus have a
considerably long bole.
The stem bears two types of
branches: (i) branches of unlimited growth or long shoots, and (ii)
branches of limited growth or dwarf shoots, also termed brachyblasts.
The long shoots appear on the main stem as lateral buds in the axils of
scale leaves. Each of these shoots terminates in an apical bud, which
is enclosed by a number of bud-scales closely surrounded by a thick mat
of hairs. The lateral buds grow more or less horizontally to a certain
length, and this growth has been termed nodal growth. In some pines
this growth is restricted to the production of a single internode every
year (uninodal pines), but in some others there may be two to several
internodes per year (multinodal pines).
The dwarf shoots or foliar
spurs develop on the long shoots, arising in the axils of scale leaves.
Each dwarf shoot initially has two opposite scales, termed prophylls,
followed by 5-13 spirally arranged, scaly cataphylls. These are in 2/5
phyllotaxy. Finally, depending upon the species, 1-5 needle-like leaves
develop. Unlike the long shoot, the dwarf shoot lacks a terminal bud.
The leaves are of two kinds: (i) the foliage leaves which appear only
on the foliar spurs, and (ii) the scale leaves, which are developed as
protective structures.
The male and female cones are
borne on the same tree, though on different branches. They become
visible towards the end of spring or the beginning of summer. The male
cones (the modified dwarf shoots) appear in clusters (catkin) on the
lower branches of the tree, whereas the female cones, which replace the
terminal buds of the long shoots, are the modified long shoots. In most
of the species, including Pinus roxburghii and P. wallichiana, the
mature female cones open and release the seeds, but in others the seeds
are released only after the cones fall to the ground and rot. In a few
species such as P. flexilis, the cones remain on the tree for several
years and open only when they are scorched by forest fire.
The pines are generally
light-demanders; a few can tolerate partial shade for several years,
but their growth is stunted. They do not thrive in areas, which remain
hot and humid throughout the year. Only a few species like P. taeda
grow successfully on wet lands. Alternation of seasons—dry and wet, and
warm and cold, or often a combination of both—is required for the
normal development of pines.
There are several external
characters, which facilitate the identification of different pines. The
number of needles per dwarf shoot, their length, the position of the
umbo on the apophysist and the shape, size and colour of the resting
bud are some of the important ones.
P. wallichiana, the blue or
Bhutan pine, commonly known in trade as Kail, is found in the Himalayas
mainly from Kashmir to Bhutan at altitudes of 1,500-3,000 m. It has
also been recorded at as high an altitude as 3,600 m along the region
of Namchebazar and Thengopoche. It is very common in the Western
Himalayas in Kashmir valley, Simla, Chakrata and Mussoorie and in the
eastern Nepal at altitudes of 1,500-2,135 m. In Bhutan, it occurs along
the valley above the river Tista (lower Rangeet valley). Though this
species is sporadically distributed along the eastern part of the
Kameng division of NEFA, it is most dominant in the Khalaktang area,
Rupa valley and the Dirang Dzong valley at an altitude of 1,500 m,
covering an extensive area along the hill slopes. In the Subansiri
division of NEFA, the species is restricted to the mountain slopes
surrounding the Apatanang valley at an altitude of 1,500-1,830 m. Here
it appears to have been introduced, since there is no trace of the
species in the surrounding mountain slopes.
The species is found on a
variety of geological formations, growing best on well-drained moist
soil with an annual rainfall of 100-200 cm. Some of the best forests
are found on mica-schist, which breaks down into ideal soil. It is
frequently associated with Cedrus deodara (Roxb). G. Don, Abies pindrow
(Royle) Spach, and Picea glauca (Moench) Voss.
The blue pine is an elegant
tree, 30-90 m high, with horizontally spreading branches. The young
shoots are glaucous green. Each dwarf shoot has five needles, 12.5-20.0
cm long, and the leaf sheaths (scale leaf, prophyll and cataphyll) are
non-persistent. The winter buds are cylindric-conic, 0.6-1.2 cm long.
The female cones are 15-30 cm long with rounded ovuliferous scales. The
seeds are winged; wings membranous, about thrice as long as the seed.
Under abundance of light and
protection, the blue pine regenerates profusely. The seeds germinate
during rainy season. If artificially regenerated, direct sowing is
preferred to transplanting. The young trees grow fairly rapidly, but on
reaching maturity the girth increment becomes slow and growth in height
may almost stop.
Kingdon-Ward reported the
occurrence of this species in the NEFA area. The tree attains a height
of 18 m and a diameter of one metre. The winter buds are cylindrical,
blunt and slightly resinous. The needles are 10-15 cm long. The female
cones are subterminal in groups of 2-3; cone is 2-5 cm or more long,
broadly tapering into rounded apex. The wingless seeds are 1.3-1.6 cm
long and are liberated soon after they ripen.
The taxonomic status of P.
insularis and P. kesiya Gord. is not satisfactorily settled. There is a
strong possibility that these two names refer to the same species.
Savory made a study of the morphology, and anatomy of the wood of these
two species. No significant difference was found between them to
justify their separation. Accordingly, Pinus insularis Endl. has been
treated by some authors as a synonym to P. kesiya Royle ex Gord. in
Loud, Gard. mag. 16: 8, 1840.
The Khasi pine is restricted
only to the eastern Himalayas, where it is commonly found along the
various ranges of the Garo. khasi and Jaintia hills (800-2,000 m). The
species has been introduced successfully in the Aijal area of the
Lushai hills (1,220 m). In the northern part of Manipur and the Naga
hills round about Kohima (1,220-1,830 m) it appears in isolated
patches. The plant grows well in fairly moist regions, free from
extremes of heat and cold on loose-textured soil like granitic or
sandstone rocks covered with clay.
The tree is 60-90 m in height
and trunk up to 6 m in diameter. The bark is thick, reddish grey and
deeply fissured giving a reticulate appearance. The branches are
arranged in whorls forming a rounded crown. The leaves are in fascicles
of threes and are 15-25 cm long, slender with acute apices. The old
needles fall for the most part during April-May, though the scale
leaves are persistent.
The male and female cones
appear on the new shoots during February-March. The mature male cones
are light brown and 3-5 cm in diameter. The female cones are
approximately 5.0-7.5 cm long and 4-6 cm in diameter and are the
smallest amongst the Indian pines. They are ovoid and initially light
green but turn brown as they mature. The prominent umbo is sharply
mucronate in the centre. The seeds have long wings, which are about
four times the length of the seed.
The plants come up naturally
in places of abandoned or shifting cultivation, or in areas where
undergrowth of forests has been burnt. For artificial regeneration the
seeds are sown broadcast. The growth rate is fairly high.
Of all the Indian pines, P.
roxburghii is the most important and is known as the Himalayan
long-leaved pine or Chir pine. It is peculiar to the main valleys of
the western Himalayas at altitudes of 460-1,500 m, and extends into
Bhutan (Biswas, 1933). Along the eastern Nepal this species is
restricted to lower elevations. In NEFA, along the Kameng Frontier
Division, it appears to be very sparsely distributed among the pure and
extensive formations of P. wallichiana. It either forms a pure forest
or occurs as a co-dominant species with other plants. At higher
altitudes, it is associated with cedrus deodara (Roxb.) G. Den, Pinus
wallichiana, ouercus inlana roxb., and Rhododendron arboreum Smith
whereas at lower altitudes, it is found along with Anogeissus latifolia
Wall., Bauhinia latifolia Cav., B. variegata L. and Shorea robusta Roxb.
P. roxburghii is a large
evergreen tree with a spreading crown. The young shoots are grey to
pale brown and the winter buds are ovoid and non-resinous. Leaves 15-40
cm long, three on a dwarf shoot. The mature female cones are 12-24 cm x
7.5-14.0 cm, the ovuliferous scales having reflexed apices. The umbo is
very prominent and the seeds are about 8-16 mm long with c. 2.5 cm long
membranous wings.
Natural regeneration is
normally through seeds. Mature cones are collected from healthy trees
for artificial regeneration, placed in hot sun to loosen the scales and
then the seeds thrashed. This is normally practised where coniferous
forests have been damaged by fire and is mostly done by direct sowing
(With India— Raw Materials, VIII).
This species is the source of
Chilgoza or Nioza seeds of commerce, which are eaten as such or after
roasting. It is found in northern Afghanistan and in the north-western
Himalayas, occurring on the borders of Tibet, Kashmir and Pakistan. It
also occurs in Kalpa (Kinnaur) and Pangi districts of Himachal Pradesh.
The plant is an evergreen
tree, 18 m or more in height and 1.8-2.4 m in diameter. It grows on
dry, rocky grounds at an elevation of 1,830-3,600 m. It thrives best in
areas where the rainfall is scanty, but winter snowfall is heavy. The
species can easily be identified by its bark, which is shed in small
flakes. The branches are ascending and are either obscurely whorled or
not whorled. They are comparatively thin, grey, with mottled
appearance. The shoots are glabrous and greyish green. The winter buds
are spindle-shaped and nearly 1.5 cm long. The stout short leaves are
c. 5-10 cm long and occur in groups of threes on dwarf shoots. The male
cones are visible during May-June, when pollination takes place. The
female cones are large, hard and woody having reflexed, triangular
umbos. Each cone is 15-20 cm × 10-13 cm.. The seed is c. 2.5 cm long
with a very short rudimentary wing.
P. merkusii is the most
tropical of all pines and is of common occurrence in the southern Shan
States of Burma. It has been recommended for planting along the eroded
hill slopes of the Andaman and Nicobar Islands. Commonly known as
Tenasserim pine, it normally attains a height of c. 20 m when mature.
The bark is grey to brown, thick and deeply fissured. The leaves are in
pairs, 17-33 cm long, persisting for 1 ½-2 years. The female cones are
cylindric, borne in pairs and at maturity reach a length of c. 5.7 cm.
The umbo is rhomboid and furrowed. The small seeds are winged.
Anatomy
Root
The plant possesses initially
a primary taproot with a large number of laterals, arising in an
acropetal succession. In most cases, the growth of the primary root
soon becomes arrested, while the laterals, termed long roots, continue
to grow. Later, the dwarf roots arise in clusters on the long roots.
They branch dichotomously and form coralloid masses. Some of these
harbour an ectotrophic mycorrhiza and are termed mycorrhizal roots.
Long roots.
In a transverse section the epidermal cells appear more or less
isodiametric and many of them are filled with tannin as in P.
roxburghii, P. wallichiana and P. gerardiana. The broad cortex is
distinguishable into a peripheral zone of small and an inner zone of
large perenchymatous cells. Frequently, the cells of both the zones are
filled with starch. The endodermis is composed of suberized cells,
usually impregnated with tannin, which gives them the brownish-orange
colour. It shows indistinct casparian-strips, followed by 6-7 layers of
pericycle. The walls of the peripheral pericyclic cells are slightly
thickened while those of the inner cells are thin. Many of them contain
tannin.
The stele is generally diarch
or tetrarch, but may sometimes show pentarch condition. The number of
protoxylem elements varies from 8 to 16. Each protoxylem point is
associated with a resin duct and consists mostly of scalariform or
scalariform-pitted tracheids, while the metaxylem is made up of pitted
trachieds. The phloem, which alternates wit the xylem strands, consists
of parenchyma, sieve and tannin cells. The pith cells contain a
considerable amount of starch; some of them also contain tannin.
Secondary growth sets in when
the primary tissues are still in the process of differentiation. A zone
of cambium differentiates from the parenchymatous cells beneath the
phloem. This by repeated periclinal divisions forms secondary xylem
towards the pith and secondary phloem towards the cortex. In the region
of the resin ducts, the cambium cuts off only parenchymatous cells,
resulting in broad xylem rays. With subsequent development of the
secondary wood, the rays are reduced to the width of only a single cell.
The secondary xylem is made
up of tracheids with bordered pits on their tangential and lateral
walls. Many tracheids get blocked with tyloses in older roots. The rays
are either uni-or multiseriate, the latter being always associated with
resin ducts.
The primary phloem soon gets
crushed and is unrecognizable. The secondary phloem consists of
radially oriented (disposed) rows of cells. Many of the parenchymatous
phloem ray cells contain tannin.
Pine Oleoresin Extraction Methods
Introduction
Modern gum naval stores
methods have been developed to benefit both the gum producer and the
timber owner. Following the methods described in this booklet will
bring maximum gum yields, will reduce chipping-labor requirements about
50 percent, and will make the worked-out tree saleable for other wood
products.
If these modern turpentining
methods are used, naval stores can be integrated in the management plan
for pine timbered lands and timber owners can almost double the dollar
value per tree by leasing or working for naval stores before they
harvest.
The aim of this booklet is to
bring together in one place all the best modern methods of producing
gum, and to describe the principal factors that affect gum flow.
The extraction methods and
application techniques described here were developed during 15 years of
research and testing by scientists at the Forest Research Institute
with the cooperation of gum producers and timber owners throughout the
gum naval stores belt.
Cup the Larger-diameter Trees for Increased Yields and
Greater Profits
A crop of single-faced trees
11 inches in diameter will produce 60 barrels more gum per year than
9-inch trees. The costs for installing tins and for chipping are about
the same for 9-and 11-inch trees. The number of small-diameter trees
worked can be the difference between break-even and profitable
operation.
Double-Facing.
Only one face per tree should be installed on trees smaller than 14
inches in diameter. Simultaneous working of two faces installed on one
tree does not mean that gum yields from that particular tree will
double. The yield from two faces worked simultaneously is normally not
more than 70 percent of the yield, which could have been obtained from
two faces, worked one at a time.
Two faces should be installed
on trees 14 inches d.b.h. and over for obtaining the greatest yield if
the trees are to be worked out in 4 years.
The volume of gum produced is
directly related to the width of the face. Good gum yields can be
obtained with a face width equal to the diameter of the tree measured
at breast height. For example, a 10-inch tree should have a 10-inch
face and a 12-inch tree a 12-inch face.
Gum
Yield from Shoulders. With bark chipping and acid treatment,
75 percent of the gum yields at each dipping flows from the shoulders
of the face. If careless chipping extends the streak ½ inch beyond the
range of the tins on each side of the face, a barrel of gum is wasted
during the season for every 310 trees worked.
Use
Correct Tin Lengths. One-piece tin assemblies or broadaxe
inserted tins will not give full-face widths on 12-inch trees and
larger. For full-face widths and good gum yields, use 10-inch spiral
gutters on trees 9 to 12 inches in diameter. Use 12 -inch spirals on
trees 12 to 16 inches in diameter. For an apron, use a 7-or 8-inch
straight or curved gutter with either length.
First-Year Installation of Spiral Gutters with Double-Headed
Nails
Shaving the Bark. Shave off
the rough bark using double-edge, shove-down scrape iron or a
bark-shave tool. Shave only the area where the tins will be nailed and
the cup will sit. Shave a fairly flat seat for the apron and cup; keep
the spiral gutter side of the tree round. Remove enough bark to get rid
of the deep cracks.
Attach the Apron First. Drive
the first nail at the middle of the apron. Level the apron and drive
the second nail in the left shoulder. Set this nail close to the end of
the tin so as to get full-face width. Drive all nails near the top edge
of the tins; this pulls the edge into the bark to prevent leakage
behind the tins. Pound the inner lip of the right-hand end of the apron
so that it fits snugly against the tree. Do not nail the right-hand end
at this stage.
Use only double-headed nails
designed specially for attaching and removing naval stores tins.
Attaching the Spiral Gutter.
Lap the lower end of the spiral gutter over the right hand end of the
apron. Set the angle of the spiral between 30 and 40 degrees - -around
30 for slash and steeper for longleaf pine. Drive the first nail in the
middle of the spiral. Drive the next nail through both the spiral
gutter and the apron at the overlap. Drive the shoulder nail last.
Close any gaps between the gutter and the bark by pounding the inner
edge of the gutter into the bark.
Completed Installation
The double -headed nails are
numbered in the photograph to show the order in which they are driven.
To support a large 2-quart cup, a 30d flathead nail is used. A
standard-size cup takes a 20d nail. Drive the cup nail at a slight
angle so outer edge of cup will snap over nail head. This holds cup
snugly against tree.
Use of the Advanced Streak
With bark chipping and acid
treatment, the familiar “lead” or advance streak is not necessary, as
it will not increase the volume of gum produced the first year from
virgin installations. An advance streak applied 30 days before the
regular chipping season begins will give good early-season yields for
the first 8 weeks of the season, but yields for the remainder of the
season will be reduced proportionally.
Producers may consider it
desirable to produce an increased volume of gum during April and May.
There may be a psychological effect in getting something in the cup
quickly to spur the interest of chipping and dipping laborers.
The best type of advance
streak for good early-season yields is a bark streak 5/8 to 3/4 -inch
high, treated with 50 -percent sulfuric acid, applied 30 days in
advance of the regular chipping season.
Turpentining and Growth
Measurement data covering a
2-year period from a plantation of 20-year-old slash pine, growing at
the rate of 8 annual rings per inch, with 15 × 15 foot spacing, and
worked with modern gum extraction methods showed that:
The annual volume increment
in cubic feet of turpentined trees was 26 percent less than that of
round, unworked trees. This reduction in growth was correlated with the
width of the face on the tree; the wider the face on a tree of given
size, the slower the growth. For normal face width equal to the
diameter of the tree, the annual deficit per turpentined tree would be
about 2 cents for pulpwood and 5 cents for saw logs, at current
stumpage prices. The gross value for naval stores per year would range
from 15 to 25 cents per tree.
Growth loss from turpentining
was not directly related to the volume of gum extracted from the tree
annually. Thus, the extent of growth loss is the same for indifferent
work and poor gum yields, as for skilled work and good yields.
Bark Chipping
The bark hack removes the
outer, rough bark and the white, inner bark, exposing the gum ducts in
the wood. Acid is then sprayed on the surface of the wood. The action
of the acid holds these gum ducts open for a period of 2 weeks. It is
the acid that makes the gum flow from the tree for the 2 -week period.
Chipping merely prepares the area for acid treatment. It is not
necessary to cut into the wood with the bark hack, because a wood
streak ½ inch deep will not produce any more gum than a streak of bark
depth, both treated with acid.
How
Often to Chip and Treat. Treating the streak with acid
prolongs the flow of gum; therefore it is necessary to chip and treat
only once every 14 days. Chipping and treating every 2 weeks during the
chipping season will get practically all of the gum the tree can
produce over a period of 4 to 6 years.
Height
of Streak to Chip. For maximum gum yields over a 4-year
period, bark streaks ¾ inch high are recommended for both slash and
long leaf pine.
Mounting and Sharpening the Bark Hack
The bark hack has been
designed with a special flat bill, square corners and high jaws to cut
through two thicknesses of bark. If it is correctly mounted and
sharpened, clean streaks can be chipped and blades will last several
years.
The angle (called “pitch”) at
which the hack head is mounted in the wooden stock helps to prevent
chipping into the wood. The best mounting angle for speedy bark
chipping is shown below.
Proper sharpening of a bark
hack blade contributes greatly to the chipping of a clean streak and
actually determines how long a blade will last.
A steel cutter may be used to
cut out and to thin the edges of a new blade, as illustrated below, but
the final sharpening touches should be with a flat file. Do not use the
cutter to resharpen the edges; use the flat file or whetstone.
Quite often laborers will
file a long, keen bevel at the bill to make woodcutting easier. But the
corners will soon break, leaving large gaps in the blade. The blade
should be filed so that the corners are kept square at all times. A
rounded or gapped corner will leave patches of inner bark in the
streak. These patches of bark will stop the flow of gum from above the
streak and reduce monthly yields.
In many instances, poor gum
yields from bark chipping and acid treatment have been traced directly
to such a simple cause as improperly sharpened hack blades. To reduce
the excessive breakage of blades, for speedier bark chipping, and for
maximum gum flow from each streak, producers should occasionally check
with their laborers on the sharpening and mounting of bark hack blades.
Treating the Streak
The difference between poor
and good yields each month is directly related to the amount of acid
properly sprayed on each freshly chipped streak.
A 50-percent solution of
sulfuric acid is used on both slash and longleaf pine. The plastic
bottle of the acid sprayer is filled only two-thirds full, and the
sprayer is held at a 45-degree angle for obtaining good treatment. Keep
the nozzle tip from 1 to 2 inches below the top of the streak and from
1 to 2 inches away from the tree. Move the sprayer in one steady motion
across the streak, spraying enough acid to wet the streak thoroughly
from shoulder to shoulder.
The sprayer should be aimed
so that the spray from the nozzle hits the streak at the line where
bark meets wood. The acid should be discharged from the sprayer in the
form of a spray. Normally, a stream of acid does not give good
treatment, because a stream hits the streak with force, spatters and
the major portion runs down the face as waste.
Good treatment is of vital
importance, and laborers must be consistently supervised to assure
quality treatment for profitable gum yields.
Acid Penetration Above the Streak
For acid treatment to be
effective, the acid must penetrate the area above the exposed wood at
the streak line. Acid penetration causes a reddish-brown color in the
white, inner bark and on the surface of the wood. Penetration above the
streak is necessary and is obtained only by good treatment, in which
the streak is wet thoroughly and evenly.
Height
of Acid Penetration. The volume of gum produced by each
streak is directly related to the distance the acid penetrates above
the streak; the higher the penetration, the greater the yield. The
penetration line and the tissues killed by acid treatment can be seen
when the next streak is chipped.
Normally, 50-percent sulfuric
acid properly applied in sufficient quantity will penetrate ½ to ¾ inch
above the streak in 14 days. Good penetration is obtained by using the
acid sprayer correctly, as the acid must be sprayed into the top
portion of the streak. Through careless application, most laborers
waste more acid per streak than is needed for good treatment.
If the height of acid
penetration is under ½ inch, then treatment has been poor, and maximum
yields will not be obtained from that streak. Poor treatment can
usually be traced to careless application.
For best gum yield, the
tissues killed by acid penetration should be removed and fresh green
wood exposed with each streak chipped. Serious yield decline may result
unless the chipping keeps up with the acid penetration.
Pines for their Oleoresin
Pines, besides being a source
of valuable timber and pulpwood, yield pitch, tar, rosin or colophony
and turpentine, collectively known as naval stores, a term coined to
these owing to their use for construction and maintenance of sailing
vessels as sealing compounds for their wooden hulls. Rosin and
turpentine are obtained by distillation of crude pine oleoresin,
exuding from the trunks of standing pine trees as a result of injury.
Rosin and turpentine are also obtained by distillation or solvent
extraction of felled pinewood and wood waste. In the paper pulp
industry, rosin and turpentine are obtained as one of the important
by-products. Pine rosin and turpentine as used in most varietal ways
and form raw material to a number of industries all over the world.
Rosin finds use in soap, paper sizing, wall board, synthetic rubber,
adhesives, paint driers, varnishes, lacquers, paints, water proofing
compounds, axle-greases, cements, linoleum, floor-waxes,
pharmaceuticals, inks etc; turpentine in paint and varnish thinning,
rosin solvent, lacquers, water proofing compounds, synthetic pine oil,
insecticides, terpene-resins, synthetic camphor, flavours and perfumes,
refined terpenes and derivatives, rubber, pharmaceuticals, polishes etc.
Geographic
distribution of pines. The pines belong to 94 recognized
species of the genus Pinus. Except one species, P. merkusii (Merkus
Pine) which crosses the Equator in Sumatra (Indonesia), in nature, all
the pines are confined to Northern Hemisphere, extending from polar
region to the tropics. A list of species, represented in the natural
flora of different countries, is given in the Appendix-I.
Pines
tapped for oleoresin. The important pine species tapped for
their oleoresin in different countries are: P. palustris (Longleaf
Pine) and P. elliottii (Slash Pine in U.S.A.; P. pinaster (Cluster or
Maritime Pine) in France, Portugal and Spain; P. Sylvestris (Scots
Pine) in U.S.S.R., Finland, Norway, Sweden, Germany, Poland, Austria,
Yugoslavia, Bulgaria and Hungary; P. halepensis (Aleppo Pine) in
Greece, France, Spain and Algeria; P. nigra (Austrian or Black Pine) in
Austria, Albania, Bulgaria, Italy, Spain, Yugoslavia, Greece and
Turkey; P. Sibirica (Siberian Stone Pine) in U.S.S.R. (Western and
Central Siberia); P brutia (Calabrian Pine) in Turkey; P. peuce (Balkan
Pine) in Bulgaria; P. pinea (Italian Stone Pine) in Northern Italy; P.
heldreichii in Yugoslaiva; P. ayacahuite (Mexican White Pine) and P.
teocota (Aztec Pine) in Mexico; P. caribea (Caribbean Pine) in
Honduras; P. roxburghii (Chir Pine) in India and Pakistan; P.
thunbergiana (Japanese Black Pine) in Japan; P. massoniana (Masson
Pine) and P. tabulaeformis (Chinese Pine) in China; P. merkusii (Merkus
Pine) in Indonesia (Sumatra Island. In U.S.A. P. taeda (Loblolly Pine)
and P. ponderosa (Ponderosa or Western Yellow Pine) are also tapped
sometimes. More than three quarters of pine-oleoresin are derived from
P. palustris, P. elliotti (U.S.S.), P. sylvestris (U.S.S.R. and
Northern Europe) and) P. pinaster (France, Italy, Portugal and Spain);
oleoresin from the former three species comprising the most of it.
Besides, following countries
have also examined various pines that are growing naturally or
introduced there, to develop their naval stores resources. They are P.
pinea in Spain; P. pithyusa, P. pallasiana, P. nigra var caramanica and
P. sylyestris var. hamata in U.S.S.R.; P. halepensis in Cyprus, Israel
and Tunisia; P. brutia in Syria; P. insularis in Burma and Philippines
P. elliottii in Argentina, Brazil and South Africa; P. radiata in
Australia, Chile and New Zealand; P. pinaster and P. caribaea in
Australia and South Africa; P. roxburghii in South Africa. P. caribaea
var. hondurensis in British Honduras; P. kesiya (P. khasya) and P.
wallichiana in India; P. taiwianensis in Taiwan, and, P. densiflora in
Japan
World
production of pine rosin and turpentine. Prior to World War
II, most of the world's supply of rosin and turpentine came from
U.S.A., and even today it tops in naval stores production. But since
then considerable advance has also been made by several other
countries, particularly U.S.S.R. and China (People's Republic), Around
1959 about 1.72 million hectares of pine forest, with an yield upto 100
Kg. crude oleoresin per hectare, were tapped in U.S.S.R. Basing on the
average of world's total production of 1964 to 1966, about 47.0%rosin
and 42.5% turpentine is produced in U.S.A., 15.8% rosin and 13.3%
turpentine in U.S.S.R., 8.6% rosin and 10.4% turpentine in China, 7.2%
rosin and 6.4% turpentine in Portugal, 3.7% rosin and 2.9% turpentine
in Mexico, 3.0% rosin and 3.5% turpentine in Spain, 2.9% rosin and 3.0%
turpentine in France, 2.8% rosin and 2.2% turpentine in India, 2.2%
rosin and 2.1% turpentine in Poland, 1.9% rosin and 2.0% turpentine in
Greece, and rest of it, i.e., about 4.9% rosin and 11.2% turpentine
collectively by 14 other countries. The estimated production of rosin
and turpentine in the different countries, during late fifties and
early sixties.
Occurrence, Formation and Exudation of Oleoresin in Pines
Occurrence.
In pines the oleoresin is formed and translocated in the resin canals,
occurring in root, wood and inner bark of the stem and leaves. The
normal resin canals are longitudinal, running parallel to axis, or
transverse, running at right angle to it. Transverse canals are always
included in the fusiform rays. The oleoresin in the longitudinal canals
tends to reach the surface by means of transverse ones. The size of
resin canals varies according to their orientation, species, age and
growth rate of trees. The longitudinal canals are invariably larger in
diameter then transverse ones. These are very large in diameter in
species like P. lambertiana (average 175-255 µ, maximum over 300 µ), P.
roxburghii (200-225 µ, and P. ponderosa; large in P. strobus (average
135-150µ, maximum 200µ), P. kesiya, (130-150µ), P. palustris, P.
elliottii, P. taeda, P. rigida and P. echinata; medium in P. banksiana
(upto 100 µ), P. contorta (60-105 µ) and P. wallichiana (70-85 µ) (106,
196, 210). Their proportion as per cent of wood volume, is 0.3% in P.
ponderosa, 0.5% in P. lambertiana 0.7% in P. strobus and 0.8% in P.
palustris. In P. peuce their number averages to 11 per linear cm. or 61
per sq. cm., and of these about 97% occur in the late wood, whereas,
the early wood contains only 3%. In all the 3 Indian pines, viz., P.
roxburghii, P. kesiya and P. wallichiana, the number of both
longitudinal and transverse canals has been recorded as 0 to 2 per sq.
mm., except the longitudinal canals in P. kesiya where it is 0 to 3 per
sq. mm. of wood; the diameters of radial canals, which are smaller than
the longitudinal ones, are 40 to 5µ, 30 to 35µ and 30 to 40µ
respectively.
Traumatic resin canals,
arising as a result of injury, may accompany transverse canals of
normal type. They may be longitudinal or transverse, but both seldom
occur together. The longitudinal traumatic canals are generally
arranged in a tangential row and usually restricted to early wood. The
traumatic transverse canals are confined to rays and are larger in
diameter than normal transverse canals. The epithelial cells of
traumatic resin canals are thick walled, whereas, these are thin walled
in normal canals.
In softwoods like pine, resin
is also contained in ray parenchyma cells, in addition to the resin
canals. The resin in epithelial cells of canals is generally fluid
type, whereas, in parechymatous cells adjacent to trachlieds it is more
viscid. Direct analysis of parenchyma resin has not been carried out
but, the proportion of canal-resin to total resin has been calculated
to be 40% in P. palustris.
Formation.
The oleoresin is produced in the epithetical cells of the canal and
adjoining living parenchymatous cells, which are especially active in
the outer sapwood. The oleoresin is under pressure exerted by the
epithelial cells into the lumen of canal; this pressure, called
oleoresin exudation pressure, is responsible for the exudation of
oleoresin when the trees are tapped. As the normal canals pass from
sapwood into heartwood, they cease to function and are frequently
occluded with tylosoids, and are gradually plugged entirely.
Evidence drawn from
reciprocal grafts of P. sabiniana and P. ponderosa was that the
oleoresin is formed locally and is not supplied from tree crown. The
site of oleoresin synthesis, in the epithelial and sheath cells of the
canals, was considered to be in the plastids and later on in the
endoplasmic reticulum. A recent study in P. halepensis allocated the
site in special organelles, i.e., spherosomes, in epithelial cells of
canals and adjacent living parenchymatous cells. These organelles were
especially active in younger tissues, which contained a higher
proportion of resin acids than the older ones. The terpenes are
suggested to be produced in the spherosomes at a later stage of their
development into the oleoresin.
Mechanism
of oleoresin-exudation. Studies have been carried out on the
anatomy of tapped faces and mechanism of resin flow in P. pinea.
Wounding causes differentiation of traumatic resin canals at that level
and the tissues surrounding the faces get soaked with resin, more
abundantly at the lower levels. The normal longitudinal resin canals,
reached by the wound, become obstructed by tylosoids formed in the
interior of the canals, and also they get elongated tangentially with
their orifices divaricated. In intact longitudinal canals, the resin is
always contained in the resiniferous cells and never runs into the
lumen. The canals interrupted by traumatic lesions on the other hand,
the secretory cells react in one of the two ways—either by turgescence,
which tends to immobilize the resin in the cytoplasm, or in following
sequence of processes the resin emulsifies in the cytoplasm, the
vacuole disappears, the nucleus degenerates, the cell membranes thicken
and turn into lamellaes, the pits enlarge and the resin exudes through
them into the lumen, and perhaps only the cells reacting in the later
fashion are able to feed the flow of resin from a wound. Resin flow
from the wound is governed by three principal conditions—a
physiological defence mechanism, consisting in a very rapid increase in
cellular turgescence leading to the occlusion of the interior of the
canal by swelling of its epithelial cells; this phenomenon which takes
place relatively far from the wound in cells of live tissues, is
accompanied by a hyper secretion of resin; emulsifying of the resin in
the water of cellular cytoplasm, its displacement, and its oozing
through the pit membranes to the interior of canal, total dehydration
of cells and embalming of their membranes by the resin giving a
characteristic laminated appearance. At the dehydration stage the resin
flow appears to cease, and it therefore seems that it is controlled by
the water in the secretory cells.
Oleoresin Tapping
The oleoresin tapping also
called "turpentining", implies in general to several operations, such
as—selection of trees, making of blaze or face on the tree, fixing of
lips and pots to collect the resin exuding from the cut-face,
freshening of the blaze, collection of oleoresin and scrape (solidified
oleoresin).
There are two methods of
oleoresin tapping which in French are termed as le gemmage a vie
(cautions or light tapping) and le gemmage a mort (tapping to death);
former method aims at obtaining the oleoresin without causing the death
to trees and is adopted for longer spells, while the second method
exhausts and kills them. The later method is adopted only when a tree
is to be felled soon after. Before introduction of cups and lips,
oleoresin exuding from the blaze was allowed to run down to the foot of
the tree, where it was received in a little trough hollowed out in one
of the roots in the sand. This practice resulted in much waste and
contamination. Hugues method, employing lips and pots, was introduced
in Landes (France) for the first time in 1844, which spread in the
region by 1885. Hugues method soon formed the basis for oleoresin
tapping in a number of countries. The salient features of principal
resin tapping methods in vogue in different countries, are described
here in brief:
1. French Methods.
P. Pinaster is the principal
oleoresin yielding species in France. Methods adopted for tapping are
as follows.
(i)
Hugues method. (a) Le gemmage a vie—This
method suggests tapping of trees 110 cm. g.b.h. or above, but often
trees of 90 cm. g.b.h are also tapped. The initial blaze is made at the
base starting a little above the ground level, preferably on the
eastern face and worked for 5 years. A second one is added on trees of
130 cm. g.b.h. or above. The season of tapping in France extends to
about 8 months (1st March to 31st October). During this period about 30
streaks or freshenings are made at 8-day intervals with an adze
(abschott) and with a rasclet when it reached higher. In a season about
6 to 7 crops are collected. Before actual tapping starts, gradual
thinning of bark to a height of about 60 cm,. and width of 15 to 20
cm., nearly reaching wood in the middle, is made as early as the 2nd
week of February.
Initially the blaze is 9 cm.
wide and is extended upward to 60 cm. height, during the freshenings by
the end of first year. Depth of the initial blaze and freshenings
increases from the sides inwards reaching a maximum of 1 cm. in the
middle. Similarly, in subsequent years, freshening is made upward in
continuation of the previous years's blaze (face).
(b) Le gammage a mort:
This method of tapping to death is used in the last 5 years of felling.
The blazes are made as close as possible in the 1st year and worked for
4 years. Generally one blaze is made on trees of 50-60 cm. g.b.h. and a
blaze is added for increase of every 20 cm. The blaze width and height
is not actually restricted in a mort tapping. Freshening of blazes is
done once or twice a week.
(ii) Bellini's method.
Bellini around 1930 introduced a new method. In this a circular
incision about 5 cm. in diameter and 2 to 3 mm. deep is made, just
sufficient to pierce below the outer bark, by a special drill like
tool. The cut is gradually enlarged during the season, upto 10 cm.
diameter and 1 cm. in depth. The face is protected by a sort of cover
"protector". The oleoresin from the blaze is led through a tube
"receptacle" into the container (bottle). This method, though
facilitated working of many faces on a tree at a time and collection of
oleoresin in pure and liquid form, retaining much more turpentine
content, did not gain wide attention owing to high labour costs.
2. Spanish Method
In
Spain P. pinaster is the principal species constituting about 94% of
the total pine stands tapped for oleoresin; the other two species,
viz., P. helepensis and P. nigra var. calabrica constituting 5 and 1%
respectively. Tapping is done on Hugues pattern, however, the Spanish
faces differ from French faces being 12 cm. wide, 3.4 m. high (final
height in 5 years) and 1.5 cm. deep. A new method called "Spanish
narrow face", was recommended for stands to be tapped for 20 to 25
years. In this system 5 narrow faces, 2.2 cm. wide, 2.2 cm. apart and 1
cm. deep, are started near the base of the tree and worked upwards
giving 19.8 cm. combined width of face, i.e., 11 cm. width of actual
tapping surface and total 8.8 cm. untapped space leftover between 1st
to 5th blazes. The method is reported to be better than standard faces
used in Spain, as it results in rapid healing of faces, 8 to 10%
greater oleoresin yield and easier to work. However, it takes longer
time in freshening. Trials are also being carried out to tap Spanish
pines employing herringbone (Mazek) system, with or without chemical
stimulation, and American bark chipping method with acid stimulation
3. Greek Method
In Greece P. halepensis and
P. halepensis var. brutia are tapped for oleoresin. Tapping schedules
follow Hugues pattern, but the standard Greek face is about 31 cm. long
(annual height) and 11.5 to 12.5 cm. wide; freshening of blaze is done
at 7-day intervals. Narrow face of about 4 to 7 cm. (Angistri Islands)
or 7 to 10 cm. (Sofika) are also employed for long term tapping of
stands where regeneration is slow.
Hydrogenless Hydrogenation of Resin
Acids
Hydrogenation of resin acids
at low pressure with palladium on carbon or platinum oxide catalysts
has been reported to yield dihydro compounds rapidly, with the
formation of tetrahydro compounds requiring more rigorous conditions.
Reduction with lithium in liquid ammonia has also been reported; the
major products are different from those of catalytic hydrogenation, as
expected. Homogeneous hydrogenation of the abietic-type, acids using
tristriphenylphosphinerhodium chloride as the catalyst was not
successful, but the pimaric- and isopimaric-type resin acids were
partially hydrogenated to the dihydro compounds.
Under
very mild conditions and in the presence of stoichiometric amounts of
water and a palladium on carbon catalyst, alkali metal formates have
been reported to be effective hydrogen donors.
This
method has been used to successfully hydrogenate soybean oil methyl
esters. We herein report that resin acids can be hydrogenated using
this method at ambient condition to form the dihydro derivatives
Experimental
The resin acid methyl ester
(0.1 mmol) was dissolved in 0.3 ml solvent in a 3-ml screwcap reaction
vial. Appropriate amounts of deionized water and sodium formate (99%)
were then added following conditions used for the transfer
hydrogenation of soybean oil methyl esters5. The reaction vial was
placed in a vortex test tube mixer to ensure mixing of all the
components before adding 5 mg of 10% palladium on carbon catalyst. The
instant of palladium addition was used as the zero reaction time. The
temperature rose slowly from ambient to 33°C-34°C over the course of
the reactions. Aliquots (2 to 3 µl) were withdrawn periodically,
diluted with Me t-Bu ether, and analyzed with an Hewlett Packard 5880
gas chromatograph (FID), using a 14-m, thin-film. DB1 column at 190°C
and a 30-m BDS column at 190°C. Components of the reaction products
were identified by their relative retention characteristics.
For the reactions at
controlled temperatures and at 5x scale. vortex mixing was replaced by
magnetic stirring.
The influence of variables on
the reactivity of the transfer hydrogenation was determined by
comparing of the initial reaction rate (ro, initial slope of the molar
fraction) as a function of time.
Results and Discussion
Resin acids were used as the
methyl esters to facilitate direct monitoring of the product
composition by gas chromatography (GC) during the course of the
reaction. Because the reaction is heterogeneous, an efficient stirring
method was needed for the small solution volumes used in most of this
study: a vortex mixer was found to be more efficient than ultrasonic
mixing. In scaling up the reactions, however, mixing could be
accomplished with a magnetic stirrer.
Methyl isopimarate, which has
an exocyc1ic double bond, was chosen as the substrate for determining
optimum reaction conditions because it reacted quickly and the expected
hydrogenation products are well resolved in GC analysis. Using an
amount of catalyst so that Pd > 0.4% and toluene as the solvent,
the effect of the proportion of water and sodium formate was
determined. Like Arkad et al. we found that 3 mol of water per mole of
sodium formate gives the most efficient reaction, whether using toluene
or a more polar solvent (50% toluene:Me-t-Bu ether) (Figure 1).
Accordingly, all further reactions were carried out with this water
content. Sodium formate is most efficient when used in a ratio of 2 mol
per mole of resin acid methyl ester, which also agrees with the results
of Arkad et al.
Transfer
Hydrogenation of Isopimaric/Pimaric Acids. Under the
conditions described and using toluene as the solvent, methyl
dihydroisopimarate was the only reaction product from methyl
isopimarate. Attempts to drive the reaction by increasing the acidity
of the system (2:1 formic acid:Na formate) were not successful.
Contrary to expectations, not only were tetrahydroisopimarates not
formed, but the reaction rate slowed considerably, probably because the
solubility of formic acid in water effectively made some water
unavailable. Solvent polarity was then increased with a water-insoluble
solvent, Me-t-Bu ether (Figure 2). Although a slight increase in
polarity had a negative effect on the reaction rate, about 1:1
toluene:Me-t-Bu ether provided the best reaction conditions. The
conversion of methyl isopimarate to dihydroisopimarate as the only
product was complete in about 1.5 h. Reaction at the ring double bond
occurred to a very small extent even after 40 h (about 5% methyl
18-isopimaranoate was formed). However, 20% of methyl
dihydroisopimarate was isomerized during this 40-hour period to a
mixture of methyl 8(14)-isopimaren-18-oate and methyl 8
isopimaren-18-oate.
Because ultrasonic waves have
been reported to accelerate many heterogeneous reactions, we tried the
isopimarate transfer hydrogenation under the most efficient reaction
conditions and ultrasonic mixing. The reaction was approximately 6
times slower than the reaction with mechanical stirring. This was
probably a result of the deleterious effect of ultrasound on
ion-exchange kinetics.
The conditions found to be
most efficient for isopimarate hydrogenation transfer were then applied
to methyl pimarate and methyl sandaracopimarate. These esters reacted
slower than isopimarate, but pimarate reacted unexpectedly faster than
sandaracopimarate (Table I). Whereas isopimarate followed a zero order
reaction path up to 95% conversion, transfer hydrogenation of
sandaracopimarate and pimarate deviated from a straight-line reaction
path earlier in the conversion.
Transfer Hydrogenation of
Abietic Acids. The best reaction conditions for hydrogen transfer for
the abietic-type methyl esters were not the same as those found for
methyl isopimarate. Both the polarity of solvent and the formate: resin
acid ester ratios were different. Optimum conditions were 4 mol of
sodium formate per mole of resinate with a solvent composition of 3: I
toluene: Me-t-Bu ether. The water: sodium formate ratio was maintained
at 3: 1. As with isopimaric- and pimaric-type methyl esters, only one
double bond was hydrogenated for all four abietic-type esters as in
disproportionation of rosin over Pd/C.II the reaction was complete in 5
to 6 h.
For methyl abietate transfer
hydrogenation, the major reaction products were
13b-abiet-8(14)-en-18-oate (64%) and 13b-abiet-7-en-18-oate (25%)
(Table II). This is consistent with the results of platinum oxide
reduction of 12-hydroxyabietic acid, in which the proportion of the 13
b-8 (14)-en isomer to the 13b-7-en isomer was nearly 3:1. Only very
small amounts of the 13 a-isomers were formed.
Although methyl neoabietate
hydrogenates faster than abietate, the initial rate of formation of the
dihydro compounds is practically the same; some isomerization to methyl
abietate (maximum about 25%) and a slight dehydrogenation to methyl
dehydroabietate occur. The reaction product distribution is essentially
the same as for abietate; only trace amounts of 13(15)-abietenoate are
produced.
For methyl levopimarate, the
side reactions of isomerization and dehydrogenation are more prevalent
(Figure 3). They do not occur if either catalyst, sodium formate, or
water are absent, which suggests that a catalyst-water/formate complex
is involved. Although a change in solvent polarity or in temperature
does not affect selectivity in the formation of specific dihydro
compounds, it does affect the extent of dehydrogenation-21% of
dehydroabietate is formed in toluene, 13.5% in 1:1 toluene:Me-t-Bu
ether, and 20% at O°C (45% at 80°C) in 3:1 toluene:Me-t-Bu ether.
Although the reaction is much faster in 3: I toluene:Me-t-Bu ether at
80°C (Ea = II kcal/mol), the yield in hydrogenated products is much
lower. The optimum temperature is about 20°C. Reducing the amount of
catalyst, decreased the reaction rate, which is in agreement with the
results of Arkad et al for soybean oil methyl esters. The amount of
catalyst had no significant influence on the selectivity of the dihydro
compounds, but the proportion of dehydroabietate increased slightly
with increasing amounts of catalyst.
The major hydrogenation
products of methyl palustrate are the 8-abieten isomers. Isomerization
of palustrate to abietate (maximum about 4%) and dehydrogenation occur
to a very small degree compared with that of levopimarate. Because the
hydrogenation products have a similar distribution for all abietic-type
esters except methyl palustrate, the reaction mechanism for palustrate
may be different.
Terpene Resins
Pale amber, transparent,
thermoplastic polyterpene hydrocarbon resins, of the type formula
(C10H16)n, have been produced and sold on a commerical scale since
1938. These resins are characterized by ring-and-ball softening points
(S.P.) ranging up to about 135º C.; they are soluble in a great variety
of organic solvents, including hydrocarbon solvents and are of good
color stability. They are used, in conjunction with other materials, in
the formulation of a wide variety of end products, including adhesives,
adhesive tapes, rubber goods, and coating compositions. Depending on
the nature of the end use, the terpene resins are supplied either in
solid form or in solution in hydrocarbon solvents; the solid forms are
made in a wide range of softening points or molecular weights.
These polyterpene resins are
derived primarily from the catalytic polymerization, in solution, of
the bicyclic monoterpene pinene, C10H16, principally the b-isomer
(nopinene), and may be regarded as essentially polymers from b-pinene.
The pinene in turn is derived from gum and sulfate turpentines, from
both of which it is recovered by fractional distillaton.
This article is concerned
only with these hydrocarbon resins, and does not cover other
terpene-derived resinous substances, such as rosins (q.v.) and the
terpene-phenol resins. The latter are produced by reacting terpene
hydrocarbons or alcohols with phenol in the presence of acid catalysts,
followed by catalytic resinification of the resulting substituted
phenol with a reactive substance such as formaldehyde. Such
terpene-modified phenolic resins exhibit among other properties
increased solubility in drying oils. They are useful in adhesives and
in various types of coatings, including particularly wax emulsions,
varnishes, paints, and heat-setting printing inks. Certain resins are
also antioxidants for rubber.
Physical Properties
The commerically available
polyterpene resins are produced with a variety of softening points
(measured by the A.S.T.M. ring-and-ball method E28-51T), ranging from +
10 to + 135ºC., corresponding to a range from viscous liquid to hard,
brittle solid polymers at ordinary temperatures. The average molecular
weights of these polymers increase as the softening points increase. A
molecular weight of about 1200 to 1250, measured cryoscopically in
benzene, is characteristic for a polymer of 125 to 135º C. softening
point. In common with polymers generally, the polyterpenses are
mixtures of polymers of various molecular weights and chain lengths. A
characteristic molecular-weight distribution obtained by fractionation
for a commercial 135ºC. softening-point polyterpene resin is shown in
Table 1. The fractionation was accomplished by partial precipitation
from amyl alcohol, the general procedure involving solution of the
resin in hot amyl alcohol, followed by cooling, decanting the amyl
alcohol solution from the precipitated higher-molecular-weight
polymers, and steam distillation of the decanted solution to remove the
alcohol. Fractions 1-0 were so obtained, increasing amounts of amyl
alcohol being required for the successive fractions because of the
decreased solubility associated with increased molecular weight.
These polymers are typically
thermoplastic, and merely soften or harden as they are beated or
cooled, no irreversible change occurring as long as the heating
temperature is kept below that at which pyrolytic reactions set in. In
common with other amorphous hydrocarbon resins, these polymers show no
sharply defined liquefaction or solidification temperatures, and their
softening points are therefore measured by arbitrary standard test
methods.
The polymers are slightly
less dense than water, resulting in a relatively high bulking value
compared to other polymeric materials. Values for the specific gravity
of these resins range between about 0.97 and 1.00, depending on the
softening point or molecular weight, the exact composition of the
monomeric terpene mixture polymerized, and the method of production.
The resins exhibit solubility
in, or compatibility with, a wide range of materials. Complete
miscibility exists with liquid paraffinic, naphthenic, and aromatic
hydrocarbons, chlorinated hydrocarbons, higher alcohols, higher
ketones, esters, and drying oils. Compatibility is exhibited with
rosin, ester gum, waxes, including paraffin wax, polyisobutylenes,
petroleum residues and pitches, mineral oils, and certain types of
petroleum hydrocarbon polymers. Under appropriate conditions,
compatibility is exhibited with rubber and modified rubbers, including
synthetic rubbers such as GR-S. Compatibility with cellulose ethers and
esters is, however, quite limited.
Inasmuch as these resins are
entirely hydrocarbon in nature they are moisture resistant and possess
good dielectric properties.
Chemical Properties
As essentially pinene
polymers, principally polymers from b-pinene, the terpene resins
exhibit properties typical of polymeric hydrocarbons including chemical
inertness. They are inert to dilute mineral acids, alkalies, and salt
solutions, and are characterized by acid numbers and saponification
numbers less than four and approaching zero. Similarly they are
resistant to heat over a wide range of temperatures, varying only in
fluidity with temperature.
The detailed chemical
structure of the terpene resins cannot be regarded as satisfactorily
elucidated. Published data in the chemical literature and patented art
have indicated these polymers to be susceptible to both halogenation
and catalytic hydrogenation, and to reaction with ozone to give
polymeric ozonides. For example, the reported weight of hydrogen
absorbed by a catalytic polymer made from b-pinene was 1.2%. This is
equivalent to 0.82 mole of hydrogen per C10H16 recurring unit in the
polymer chain. Based in part on these considerations, and in part on
physical properties, Roberts and Day speculated that the catalytic
polymerizaton of b-pinene involved more than a simple chain addition
reaction of monomer molecules and that isomerization occurred during
the polymerization to give a polymer comprising a chain of recurring
monocyclic C10H16 terpene units each containing a carbon double bond.
Powers has also suggested the recurring unit of polymers pinene to be
monocyclic and unsaturated, proposing a formula different in detail and
in point of linkage.
More recent studies of these
polymers by infrared spectrophotometric techniques have indicated that
the polymers contain notably less unsaturation that would be required
for a chain of recurring monocyclic terpene units but more than would
be the case for a simple addition polymerization of b-pinene molecules
yielding a polymolecule containing only a single terminal double bond.
Part, but not all of the unsaturation observed by infrared examination
appears to represent terminal double bonds in the polymolecules
inasmuch as it decreases with increasing molecular weight.
These observations imply that
the pinene polymerization is, as postulated by Roberts and Day, more
complex than simple addition, but that the final recurring unit
structure is not solely monocyclic. Pending further elucidation it
seems preferable toavoid the term poly-b-pinene, insofar as the latter
may imply simple addition polymerization.
Terpene Based Adhesives
Introduction
Terpene resins are low
molecular weight hydrocarbon polymers prepared by cationic
polymerization of terpenes. These products, used by the adhesives,
sealant, wax coating and investment casting industries, are separated
into three major categories: pressure sensitive adhesives, hot melt
adhesives and coatings, and elastomeric sealants. The pressure
sensitive adhesives category includes solvent, emulsion, and hot melt
pressure sensitive adhesives and rubber cements. The hot melt adhesives
category includes hot melt adhesives, coatings, and investment waxes,
while the elastomeric sealants category includes sealants, caulks and
can end cements. Specific types of tackifying resins are required for
each use.
Terpene resins are old, in
fact, the oldest reference to polymerization was recorded in 1789 where
in turpentine was treated with sulfuric acid. More modern milestones
are a U.S. patent issued to Emile Rouxeville in 1909 for subjecting
hydrocarbons such as turpentine to sulfuric acid to produce a resin and
to resemble various Indian rubbers. Twenty-four years later, aluminium
chloride catalysis was patented for terpene polymerization, by the Gulf
Refining Company. Later, in 1950, an excellent fundamental publication
by Roberts and Day appeared in the chemical literature. Commercial
terpene resins produced for adhesive applications resulted from
modification of disclosed processes, catalysts and terpene feed stocks.
Chemistry
Commercial tackifying resins
are prepared from the monoterpenes (Figure 1). Beta-pinene,
alpha-pinene and dipentene (limonene) are derived from turpentine by
fractional distillation. The supply of dipentene is augmented by
by-product linonene collected during processing citrus fruit to frozen
concentrate.
Commercial beta-pinene
typically ranges from 72-95% purity. Beta-pinene resins are prepared
from the lower assay material and flavour fragrance chemicals from the
higher. Dipentene and alpha-pinene resins are generally prepared from
92-98% pure feedstreams. Smaller quantities of modified terpene resins
are produced from mixed feeds of terpenes, phenols, and hydrocarbon
monomers.
Beta-pinene resins
Initiation
The effective catalyst for
terpene polymerization is a complex protonic acid derived by the
interaction of a Lewis acid, typically AICI3, and a cocatalyst or
promoter such as adventitious water. The initiation step is completed
when the “hot” proton produced attacks the exocyclic methylene group of
a beta-pinene monomer (Figure 2).
Propagation
The tertiary carbenium ion
rearranges prior to its attack on another monomer, which begins the
propagation step (Figure 3). The main repeating unit in a beta-pinene
resin is a ring having 1-4 disubstitution.
The resin can be visualized
as a perfectly alternating copolymer of isobutylene and cyclohexene.
Its chemistry can be explained on this basis.
Ozonolysis or peracid
oxidation indicates and olefinic group per mer unit. Infrared analysis
shows the expected gem di-methyl group of the repeat unit and the
single methyl of the end unit.
Termination
The overriding determinant of
molecular weight is chain transfer. This limits molecular weight to the
1000-2000-unit range as determined earlier by Roberts & Day.
Figure-4 depicts the rearrangement of the end mer through ring
expansion to a (2:2:1) bicyclic system and loss of a proton to form a
camphenic end-group. The camphenic carbenium ion depicted in Figure-4
will be non-propagative for steric reasons. Good analogy for this
rearrangement mechanism to a non-propagative camphenic end cited above
is seen in the acid-catalyzed Wagner-Meerwein isomerization of alpha-or
beta-pinene, which expands the four membered rings to the (2:2:1)
bicyclo ring system (Figure-5). A second minor chain transfer step to
aromatic solvent, also occurs during commercial manufacture. In this
case, the growing end attacks the solvent with elimination of a proton
to produce the end-group shown in Figure-6.
Dipentene Resins
The initiation step is
similar to that described previously for beta-pinene resins.
Propagation through the terminal methylene group would be predicted
(Figure-7). However, the determination of olefin content by NMR,
ozonlysis and perbenzoic acid oxidation indicates that only one-half of
the mer units have the expected unsaturation. The endocyclic or ring
double bond is involved in the polymerization and is consumed in some
manner. To explain these facts and elucidate the polymerization
pathway, the structurally similar model compound 8, 9-p-menthene
(Figure-8) was subjected to polymerization conditions.
Only dimer was obtained,
therefore the presence of a double bond in the ring is required for a
successful polymerization. Armed with this fact, me may theorise that
the polymerisation of dipentene proceeds by initiation at the
tri-substituted olefinic ring position with the carbenium ion
under-going cyclic polymerization to yield a structural unit as shown
in Figure 9.
Butler has shown that the
polymerization of the related 1-methylene-4-vinylcyclohexane proceeds
partially by cyclization (Figure-9). More likely, the terminal
isopropyl carbenium ion attacks the residual double bond of the
penultimate mer unit and thus forms a ring with subsequent
polymerization proceeding from the penultimate mer unit.
A structural representation
based on this postulation is presented in Figure-10. The dotted bonds
are those formed during polymerization, the Arabic numerals indicate
the sequence of bond formation, and the letters the dipentene mers. By
invoking either of the above mechanisms, we can satisfactorily explain
the presence of only one double bond per every two to three mer units.
Further evidence of the polycyclic nature of the resin is the high
density of the dipentene resins.
Alpha-pinene resins
This monomer is the most
difficult of the common terpenes to polymerize since it does not
possess an exocyclic methylene group. Although alpha-pinene easily
forms the same initial carbenium ion as beta-pinene (1), the
propagation step, Figure-11, is difficult for steric reasons. The
presence of an adjuvant is required to eliminate the formation of large
amounts of dimer which otherwise would form during the polymerization.
The presence of the adjuvant
(also referred to as a synergist) is thought to stabilize the growing
carbenium ion and thus give it a longer lifetime during which it can
attack another alpha-pinene monomer. Chain transfer to monomer is thus
suppressed with its accompanying formation of dimer (Figure-12). The
peracid oxidation of alpha-pinene resin shows that approximately
two-thirds of the mer units contain an olefin indicating that in the
remaining one-third, the four membered ring probably expands and
results in a saturated mer unit possessing the (2:2:1) bicyclic system.
Accordingly, the two proposed mer structures (a) and (b) in an
alpha-pinene resin are illustrated in Figure-13.
Physical characteristics of resins
The number average molecular
weights and molecular weight distributions of representative commercial
terpene resins, determined by vapor pressure oxmometry and gel
permeation chromatography, are presented in Table 1.
The molecular weight is the
most important single property of a polyterpene resin. It may be
correlated to physical properties and utility. When a polymer property
is plotted versus molecular weight, there occurs a “leveling off” in
the property at a particular molecular weight, which varies for each
resin or polymer. In most instances it is necessary to attain this
minimum molecular weight range to get the desired physical properties,
e.g., polypropylene has to have a molecular weight of 50,000 and
acrylonitrile 35,000 to be useful in common polymer applications. By
contrast, the relatively low molecular weights of terpene resins at
which properties plateau, coupled with their narrow molecular weight
distribution and excellent solubility in elastomers makes them unique
and useful for adhesives.
An adhesive consisting of a
high polymer and a low molecular weight tackifier takes advantage of
the properties of each component. The high polymer contributes strength
through entanglements of extremely long chains and rein-forcement with
secondary valence bonds, whereas terpene resins attain their utility
from low molecular weight, rapid change in viscosity with temperature,
Newtonian liquid behaviour and good solubility which provides high
polymer segmental motion and wetting of substrates. It is recognized
that the preferred tackifiers for pressure sensitive tapes are
beta-pinene resins having ring and ball softening points from 115ºC to
135ºC. This maximum utility appears on the bend or leveling off of the
softening point molecular weight curve (Figure 14). At this bend, the
beta-pinene resins are transparent amber glasses. Recently, water white
versions have been introduced.
Since initiation, propagation
and chain transfer process are all proceeding simultaneously, we
observe a distribution of molecular weights. This can be determined by
gel permeation chromatography. During a typical batch polymerization,
the molecular weight distribution was observed to change during the
course of the monomer addition. This is not surprising in view of the
multitude of physical changes that are occurring, e.g., the
heterogeneous to near homogenous catalysis, the increase in dilution.
In order to better control the polymerization process, most commercial
operations employ a continuous process where a steady state ration of
initiation/propagation/chain transfer is present. (cf. Commercial
Production).
For a specified softening
point, dipentene and alphapinene resins have lower molecular weights
than a betapinene resin indicating that the former polymer structures
are more rigid and more compact than that of a beta-resin. The density
of dipentene resins is higher than that of beta-resins, 0.998 to 0.974,
corroborating the presence of rigid fused ring moieties. Although
dipentene resins have a higher softening point/mer unit, they have a
smaller hydrodynamic volume and hence form solutions of low viscosity.
The semi-ladder structure is confirmed by greater thermal stability
than betapinene resins. The density of alpha-resins, at 0.976, is very
close to that of beta-resins; more importantly, the molecular weight
and hydrodynamic volume are closer to those of dipentene resins that
beta-resins. For this reason, the bulk properties of alpha-resins
resemble those of dipentene resins with the exception of thermal
stability. The thermal stability of alpha-resins is poorer because of
the partial steric interaction due to the 1-3 disubstitution of the
cyclohexene ring and absence of any double stranded placements.
Pressure sensitive adhesives
A pressure sensitive adhesive
is one which is permanently tacky, requires no activation by heat,
solvent, or moisture, and which will adhere strongly to most surfaces
upon application with a minimum of pressure. Tack is defined as instant
low order adhesion developed by mere contact with a variety of
dissimilar surfaces. The major components of a pressure sensitive
formulation are elastomer and tackifier. The latter can be polyterpene,
hydrocarbon or rosin ester-based. The elastomers, generally rubbers,
have molecular weights between 60,000 and 350,000, which correspond to
degrees of polymerization of 1,000 to 5,000. Because of their extreme
chain length, they provide the cohesive strength to formulation and, in
addition, possess a latent tackiness. Their high molecular weights
allow modification with large amounts of other substances without
serious loss of cohesive strength. The terpene resins, because of their
chemistry and physical characteristics, combine with the elastomer to
produce formulations with the characteristics of tack, adhesion and
cohesion required of a successful pressure sensitive adhesive.
The tackifying resin can be
thought of as a solid solvent for the rubber elastomer. Usually,
solubility is affected by molecular weight; the smaller the molecule,
the higher the solubility. While low molecular weight in a tackifying
resin is desirable, there is a practical limit to this feature. As
molecular weight drops, semisolid resin is produced which imparts tack
but adhesives formulated with such a resin then fail cohesively.
Conversely, adhesives made with resins having a softening point beyond
135ºC lack in tack. Empirically, beta-pinene resins of 115ºC softening
point impart the best balance of adhesive properties.
The tackifying resin appears
to operate by bringing out the smaller, tack-bestowing molecules from
their dispersion in the mass of the rubber. The solubility of the
longest chains of a rubber is at best limited, so we can speculate that
the tackifying resin exhibits a gradient solvent effect—totally
solubilising the shortest chains, partially solubilising those of
intermediate large size. In the case of the longest elastomer chains,
the tackifier probably operates by solubilizing segments, thereby
allowing wetting of the substrate and adhesion.
Ozonolysis of Alpha-Pinene
The discovery that the esters
of pinic acid (2,2-dimethyl-3-carboxy-cyclobutylacetic acid) have
excellent lubricant and plasticizer properties has stimulated interest
in this compound and in its precursor, pinonic acid
(2,2-dimethyl-3-acetyleyclobutylacetic acid). The cost of producing
these acids by permanganate oxidation of a-pinene to pinonic acid and
further oxidation to pinic acid with hypochlorite is expensive. On the
other hand, an ozonolysis process might be developed which would be
economically attractive. Harries and coworkers made a cursory
investigation of the ozonolysis of a-pinene and reported about 25%
yields of a liquid pinonic acid. Subsequently Brus obtained low yields
of solid optically active pionic acid by decomposition of an ozonide of
a-pinene. More recently, Spencer and coworkers have reported that vapor
phase ozonization of a-pinene yields an ozonide containing five atoms
of oxygen which yields pinonic acid. They question the validity of
Harries identification of pinonic acid.
Prior of the initiation of
the research reported here, workers at the Naval Stores Station of the
United States Department of Agriculture, Southern Utilization Research
Branch, had verified the fact that pinonic acid is actually obtained by
liquid phase ozonoloysis of a-pinene using low concentrations (2%) of
ozone and had increased the yield of pinonic acid to about 50%. This
work consists of a broad screening program of the effect of a number of
variables on the production of pinonic acid and pinic acid by the
ozonolysis of a-pinene in the liquid phase using concentrations of
ozone up to
100%.
The structural formulas of the principal compounds are
Effect of solvent, ozone concentration and temperature on
yields were investigated
Solvent
Screening. The data obtained from an evaluation of the effect
of solvent are listed in Table 1. Except for those from experiments
involving the use of acetic acid and carbon tetrachloride-acetic acid
as solvents, all data in Table 1 resulted from single experiments,
unless otherwise indicated. The best of several experiments with each
of five selected solvents, involving changes in concentration of ozone,
ratio of ozone to pinene, and ozonization temperature, are listed in
Table 1 with the footnote about multiple runs. In view of the apparent
superiority of the carbon tetrachloride—acetic acid solvent system,
this system was investigated in some detail.
Ozone
Concentration. The ozonization of a-pinene in carbon
tetrachloride—acetic acid solvent was studied as a function of ozone
concentration in order to ascertain the possible advantages of the use
of high concentrations of ozone. The technical literature does not
contain any references to the use of high concentrations of gaseous
ozone in the controlled oxidation of organic compounds.
A series of ozonolyses was
made with 7.5, 15 and 100 mole % gaseous ozone during the ozonization
phase, followed by a 0.5- hour reflux treatment. The data for these
runs are presented in Table 2. The fact that the yields for all these
runs are so nearly the same strongly suggests that the yield of desired
products is independent of the concentration of gaseous ozone used.
Effect
of Temperature. The effect of temperature on the ozonization
of pinene in carbon tetrachloride—acetic acid solvent was investigated.
These data, comprising a part of Table 3 suggest that there is only a
slight increase, if any, in the yield of pinonic acid caused by
changing the temperature of ozonization from 25º to 5º or -40º C.
Carbon tetrachloride—acetic acid
solvent composition and ratio of pinene to ozone during ozonization do
not substantially affect yields
The data acquired on the
effects of solvent composition and the ratio of pinene to ozone on the
ozonization of pinene in carbon tetrachloride—acetic acid solvent is
presented as part of Table 3. These data suggest that changes in these
variables do not effect any pronounced changes in the yield of pinonic
acid. It appears that slightly better yields are obtained when a large
excess of ozone is used.
Post-Ozonization
Use of Dilute Ozone. An investigation was made of the
post-ozonization use of a very dilute ozone (1000 p.p.m.) in oxygen at
the reflux temperature of the liquid phase, compared with simple
refluxing. The data for these experiment are listed in Table 4.
In five of the six
comparisons made between the use of simple refluxing and the use of
1000 p.p.m. ozone, the use of ozone slightly increased the yield of
desired products. The results of three series of experiments, designed
to test the effect of using dilute ozone over a long period of time,
suggests that little or no increase in the yield of desired products is
obtained by using 1000 p.p.m. ozone for more than 2 hours. The results
of a single pair of experiments, designed to explore the advantages of
using more concentrated ozone for post-ozonization treatments, suggests
that the use of 2000 p.p.m. ozone may be more beneficial than 1000
p.p.m. ozone.
Experimental conditions are discussed
Analysis
for Products. An aliquot of the final ozonolysis system,
stripped of solvent, was dissolved in chloroform and
chromatographically analyzed by the method of Marvel and Rands.
Department of Agriculture, Olustee, Fla., and our own study of known
mixtures of pinonic acid, terebic acid, and pinic acid. The percentage
of butanol in chloroform for the three elution solvents used were 0, 1,
and 2, respectively. To each 10-ml. fraction eluted, 15 m,. of 95%
ethanol was added prior to titration with standard alkali to the phenol
red end point.
Ozonization
with Dilute Ozone. Dilute ozone of known concentrations was
prepared by vaporizing a known quantity of 100% liquid ozone in an
evacuated reservoir of known volume and adding pure nitrogen or pure
oxygen until 2 atmospheres pressure (absolute) was obtained. A given
amount of the dilute ozone was then bled through a grooved stopcock and
rotameter at 10 liters per hour through the reactor containing the
solution of pinene. The reactor (for runs with an excess of pinene over
ozone) was essentially a 28 × 200 mm. test tube with a short 45º side
arm about 125 mm. above the bottom of the reactor, with a 24/40
standard taper joint permitting connection with a reflux condenser and
exhaust gas tube. An 8-mm. outside diameter glass gas inlet tube was
concentrically sealed to a male 24/20 standard taper joint, which
fitted the top of the reactor tube. The gas inlet tube terminated about
15 mm. from the bottom of the reactor with a coarse fritted
borosilicate glass pencil, 12 mm. outside diameter, or a finely
perforated endsealed glass tube.
During
ozonization, the reactor was surrounded by 530 ml. of water (or other
appropriate coolant), held in a open widemouthed Dewar flask. The
jacketing water was stirred intermittantly during the ozonization
period and a temperature rise of approximately 4º C. was usually
observed for each 0.95 gram of ozone passed into the reactor.
Ozonization
with 100% Ozone. Liquid ozone and high concentrations of
gaseous ozone are highly reactive with iron, brass, mercury, rubber,
ordinary greases, and many organic and inorganic compounds. Glass,
stainless steel, aluminum, concentrated sulfuric acid, and
perhalogenated hydrocarbons are compatible with ozone. Ozone handling
apparatus must be cleaned serupulously before using.
The apparatus for conducting
ozonizations with 100% ozone is as follows: The liquid ozone tube is
connected to one arm of an inverted U-tube by a ball and socket joint.
The shallow U-tube is made of 1-mm. capillary tubing and is
approximately 2 ft. long in the horizontal direction. The other arm of
the U-tube terminates in a male standard taper 24/40 joint
concentrically ring sealed about the capillary tube which extends about
3 cm. beyond the joint. An outlet or exhaust tube, made of 0.5 mm.
capillary tubing, extends from the upper side of the 24/20 joint about
a centimeter below the ring seal. Standard round bottom flasks are
attached to the 24/40 joint.
w-Bromolongifolene
Abstract—By analogy with
w-bromocamphene, w-bromolongifolene on fusion with alkali, but at a
comparatively higher temperature, gives several monomeric and dimeric
products as a result of right enlargement. The monomeric products have
been characterized as longihomocamphenilone (VIII) and
longi-isohomocamphenilone (IX). The dimeric products are composed of a
mixture of longifolenyl ethers and the kinetic dimers. Lead
tetraacetate oxidation of longifolene, according to the method of
Ourisson, has been found to yield, not only longihomocamphenilone and
longidione, but also a crystalline alcohol, identified as isolongifolol
(XI).
Base induced ring enlargement
of w-bromocamphene was first studied by Lipp. He observed that
potassium hydroxide fusion of w-bromocamphene affords a six-membered
ring ketone and divinly ether as dimeric product. Later, Huckel also
investigated these reaction products, but only recently Wolinsky after
reinvestigation, characterized the constituents as I to V.
Longifolene (VI), which in
many reactions is similar to camphene, also forms w-bromolongifolene
(VII). Ourisson attempted alkaline fusion of the w-bromo compound (VII)
without success. A reinvestigation of the alkali fusion of
w-bromolongifolene has produced interesting results, which we wish to
place on record.
During the initial alkali
fusion of w-bromolongifolene, using the method described by Wolinsky
for w-bromocamphene, the bromo compound was recovered unchanged.
Considering the structure of longifolene and is general inertness, it
was felt that the conditions for alkali fusion mentioned by Ourisson
might not be applicable and hence certain modifications in the reaction
were employed. After several attempts by varying the temperature of
fusion, it was found that a temperature range of 380 to 400º is
required. Instead of glass tubes, a stainless steel tube fitted with a
long air condenser was found necessary for the drastic conditions
employed.
As in the case of the camphene
series, the fusion products were steam distilled and the distillate and
the residue worked up separately.
Steam distilled products
By judicious application of
GLC and TLC, the product was found to be a mixture of four components,
the identification of which was carried out by employing both physical
and chemical methods. Actual separation of these components was
achieved by elution chromatography. Of the four, two were identified as
longifolene and unreacted w-bromolongifolene. The other two were found
to be ketones (5-7% yield). IR spectra of these showed close similarity
and indicated that both are six-membered ring ketones with a —CH2—CO—
linkage, but they are different as shown by GLC, TLC and NMR studies.
One of the ketones (IR
spectra, Fig. 1; NMR spectra Fig. 3) agrees perfectly with the ring
enlarged ketone longihomocamphenilone (VIII), prepared by Ourisoon6 by
lead tetraacetate oxidation of longifolene. On the basis of chemical
and NMR spectral evidence he proved the structure as being VIII, the
second ketone (obtained by us) must, therefore, have the structure IX
and the name longi-isohomocamphenilone (IR spectra Fig. 1; NMR spectra,
Fig. 4) is proposed. In conformity with this, both these ketones give
longidione (X) on treatment with selenium dioxide.
While preparing standard
longihomocamphenione (VIII) for comparison purposes by lead
tetraacetate oxidation of longifolene according to the procedure of
Ourisson, together with longihomocampheilone (VIII) and longidione (X),
substantial amounts (5%) of another compound, an alcohol, which has
been characterized as iso-longifolol (XI) was isolated. Its identity
was further confirmed by oxidation to iso-longifolic acid (XII).
Residue
The
reside from steam distillation of the alkaline fusion product was
purified by repeated chromatography and distillation under diffusion
pump vacuum and the purity examined by TLC using silica gel impregnated
with silver nitrate.
The product was found to be
mostly dilongifolenyl ether dimer (XIIIa and b), since it has an
absorption maximum at 6.05µ (1653 cm–1) which supports the presence of
a vinyl ether, revealing that the alkaline fusion of VII predominantly
produces a unique ring expansion. The ketone dimers (XIVa and b) which
as in the camphene series, might also be present, could not be
isolated. Although their presence is not supported by UV absorption, a
positive indication comes from ozonolysis of the dimeric product, when
both the ketones (VIII and IX) and the diketone (X) are produced. The
presence of a divinly ether was established by chromic acid oxidation
to furnish longihomocamphenilone (VIII), longi-isohomocamphenilone
(IX), longidione (X) and longiforic acid (XV).
All m.ps and b.ps are
uncorrected. Rotations were taken in CHC13 solution. IR spectra were
taken as liquid films for liquids and in nujol for solids on a
Perkin-Elmer Model 137B Infracord spectrophotometer by Ms. Gopinath and
Deshpande. The NMR spectra were taken in CC14 solution using
tetramethylisilane as internal standard on a Varian A-60 spectrometer
by Dr. Nair and Mr. Mulla. GLC analyses were carried out on a
Griffin-George instrument on polyester column using H2 under press. as
the carrier gas by Ms. Bapat and Sankpal, Anhydrous Na2SO4 was used for
all drying purposes. Microanalyses were carried out by Mr. Pansare and
colleagues.
w-Bromolongifolene (VII).
This was prepared according to the procedure of Ourisson with some
modifications. To a mechanically stirred solution of longifolene (100
g) in dry ether (300 ml), Br2 in dry ether (500 ml) was added at —10º
during 3 hr and further kept at the same temp for ½hr. The mixture was
then kept in a freeze for overnight. The ether was removed in vacuum at
20º, dimethylaniline (200 g, 3 equivs) added and the mixture heated for
7hr at 180º. It was acidified with HCl aq (1:1), extracted with ether,
washed thoroughly with water until free of acid, dried, the ether
removed and the residue fractionally distilled to yield pure (GLC, TLC)
w-bromolongifolene (43-45%), b.p. 150º/6 mm, m.p. 40-41º. (Found: Br,
27.94. C15H23Br requires: Br, 28-02%).
Fusion of w-bromolongifolene
with potassium hydroxide. w-Bromolongifolene (2-5 g) and KOH (6-15 g)
were placed in a stainless steel tube (length 8", diameter 1") fitted
with a long air condenser. The contents were heated on a sand bath and
the temp slowly raised to and kept at 380—400º for 1½ hr. After cooling
the tube the contents (dark brown) were poured into water. Several such
fusions (from 90 g of VII) were combined together and steam distilled.
The distillate and the residue were worked up separately.
Longihomocamphenilone (VIII)
and longi-isohomocam-phenilone (IX). The steam distillate was extracted
with ether, washed, dried and the ether removed. The residue (22.5g)
was chromatographed on alumina (gr. 1, 675 g) and eluted successively
with pet. ether, benzene and ether.
Pet, ether eluate (15.5 g)
was found to contain a mixture of longifolene and unreacted
w-bromolongifolene, which were separated by repeated chromatography and
characterized by GLC, TLC. and IR analyses.
The earlier fractions of the
benzene eluates and the later fractions of the ether eluates were rich
in the ketones (IX and VIII) respectively. The intermediate fractions
were a mixture of these two ketones. By careful and repeated
chromatography of the appropriate fractions, these two ketones were
obtained in the pure form (GLC and TLC) and were further purified by
sublimation.
Longihomocamphenilone (VIII;
yield 2 g). It had m.p. 55-57º, (a)D + (91.26º (c, 7.15). (Found: C,
82.04; H, 10.64. C15H24O requires: C, 81.76; H, 10.98%). 2,4-DNP
derivative, m.p. 144º, (Found: N, 14-23. C21H28O4N4 requires: N,
14.01%).
The same ketone prepared from
longifolene by treatment with lead tetraacetate according to the method
of Ourisson showed the same m.p. (55-57º) but a higher specific
rotation (141.6º). The m.ps of the DNPs of our ketone (144º) and the
Ourrison’s ketone, as obtained by us (144-145º), were also somewhat
lower than observed by Ourrisson (156-158º). However, GLC and TLC
behaviour and the IR and the NMR spectra of our ketone were identical
with Ourrison's ketone, thus proving their identity. It may be possible
that partial racemization has taken place during help temp alkali
fusion, which will explain the lower optical rotation.
Long-isohomocamphenilone (IX
yield 2 g). It had m.p. 52.53º, (a) D + 64.13 (c, 1.45). (Found : C,
82.08; H, 10.79. C15H24O requires: C, 81.76; H, 10.98%). 2,4 DNP
derivative, m.p. 166º. (Found: N, 14.45. C21H28O4O4 requires: N,
14.01%).
Selenium dioxide oxidation of
longihomocamphenilone (VIII) and longi-isohomocamphenilone (IX) to
longidione (X).A solution of SeO2 (150 mg) in a few drops water and
acetic acid (2 ml)
was added to a solution of longi-isohomocamphenilone (56 mg) in glacial
acetic acid (2ml) at 80º and the mixture heated on a water bath for 24
hr. It was then diluted with water, extracted with ether, the ether
extract washed with water, dried and the ether removed. The solid
diketone was crystallized from pet. ether as fine yellow crystals;
yield 50 mg, m.p. 93-94º, mixed m.p. with authentic sample undepressed,
IR bands at: 2960; 1730 and 1700 (doublet), 1497 and 1370 cm-1. (Found;
C, 77.05; H 9.61. C15H22O2 requires; C, 76.88; H, 9.46%).
The similar odixation of
longihomocampheilone (VIII) gives the same product.
Dilongifolenyl ether (XIII a,
b). The residue from steam distillation of the alkaline fusion products
was extracted with ether, washed with water till neutral, dried and the
ether removed to yield a viscous dark brown product (35g). It was
chromatographed over alumina (Gr.II, 1kg). On distillation it afforded
a viscous, light yellow oil, b.p. 215º (bath)/1.54 × 10–2 mm; IR bands
at: 2941, 1653, 1449, 1370, 1205, 1176, 1156, 1130, 1093, 1036, 980,
926, 830, and 820 cm–1. (Found: C, 85.92; H, 11.18. C30H46O requires:
C, 85.24; H, 10.97%).
Chromic acid oxidation of dilongifolenyl ether
The ether (2.5 g) and CrO3
(1.7 g) in acetic acid (18 ml) were heated on a water bath for 1 hr.
Potassium carbonate (20g) was added to the green solution and the
mixture steam distilled. The distillate was extracted with ether
affording a yellowish oil (0.7 g), shown to be a mixture of
longihomocamphenilone, longi-isohomocamphenilone and longidione by GLC
and TLC analyses and further confirmed by actual isolation via
chromatography over alumina.
The residue left after steam
distillation of the product of chromic acid oxidation was made slightly
acidic. The organic material was extracted with ether and divided by
treatment with alkali into acidic and neutral portions. The former,
which was composed of longiforic acid (XV), was crystallized from ethyl
acetate, m.p. 220-221º.
Ozonolysis of dilongifolenyl
ether. A solution of the ether (1.14 g) in CCl4 (20 ml) was ozonized at 0º for 4 hr.
Carbon tetrachloride was removed under vacuum and the residual ozonide
was heated with water (20 ml) for 2 hr extracted with ether. The ether
extract was separated into acidic and neutral portions by treatment
with KOH. There was very little acidic material. The neutral portion, a
yellow oil (1 g), was shown to be a mixture of longihomocamphenilone,
longiisohomocamphenilone and longidione by GLC and TLC analyses and
further confirmed by actual isolation via chromatography over
alumina.
Peroxides from Turpentine
Excellent activity of pinane
hydroperoxide as a catalyst for 5ºC.GR-S polymerization was reported in
the first article in this series. At that time attention was called to
the fact that unusually high conversions and yields of the
hydroperoxide can be obtained from pinane. This article discusses in
greater detail methods of producing technical grades of pinane
hydroperoxide from gum turpentine in good yields. The preparation and
properties of pure cis-l-pinane-2 hydroperoxide have been described.
From gum turpentine or
pinenes, four steps are involved in producing technical grades of
pinane hydroperoxide:
1.Conversion
of pinenes to pinane by hydrogenation
2.Purification
of the pinane, usually by distillation
3.Oxidation of purified pinane with
molecular oxygen to give an oxidate having a peroxide content of about
50%
4.Stripping
of the oxidate under vacuum to remove unoxidized pinane and leave the
pinane hydroperoxide as the residue.
The product prepared on a
20-mole scale had a purity of 85 to 90% A conversion of at least 40%
per pass and a yield, based on pinane not recovered, of 80 to 90% was
obtained.
Peroxide number and degree of unsaturation are tests of
product quality
Peroxide
Number. The peroxide content of the various oxidates was
determined by a slight modification of the iodometric method of
Wheeler. The reaction time was 5 minutes and the results are expressed
as peroxide number in milliequivalents per kilogram. The peroxide
number of pure pinane hydroperoxide is 11,760.
Unsaturation.
The quantitative hydrogenation method of Joshel and coworkers was used
to determine unsaturation in the various products. The results are
calculated in terms of moles of hydrogen absorbed per 136 gross of
sample. For convenience, these values are referred to double bonds per
mole in the case of turpentine and are converted to percentage of
olefins in the case of crude pinanes.
Sulfuric
Acid Test. For rapid control the purposes purity of freshly
prepared pinane was estimated by shaking a portion with an equal volume
of 85% sulfuric acid for 1 minute and examining the acid layer. Samples
that give a cloudy acid layer or a straw color darker than 0.05N
potassium dichromate solution will generally be unsatisfactory.
Catalytic hydrogenation of pinene to pinane is first step in
hydroperoxide production
Pinane is prepared by
catalytic hydrogenation of either a-or b-pinene. In the work reported
in this article a commercial catalyst containing 16% nickel supported
on filter aid and suspended in coconut oil was used. Both high pressure
(20 to 100 atm.) and low pressure (15 to 30 pounds per square inch
absolute) hydrogenations were made using this catalyst at a 1% nickel
level and temperatures in the range of 60º to 150º C.
High
Pressure Hydrogenation. In a representative high pressure
hydrogenation, 1275 grams of fresh gum turpentine, = 1.4715, = 12.60 (10 cm., neat), = 0.8618 containing an
average of 1.03 double bonds per mole were charged to a 3-liter,
rocker-type autoclave. Commerical nickel hydrogenation catalyst (70
grams, 14 grams of nickel) was added and the autoclave was closed,
flushed with hydrogen, and charged with hydrogen at about 100 atm. The
shaker was started and the autoclave was heated electrically to about
60º C. over a period of about 20 minutes by means of an electric
furnace. At this point the hydrogenation "caught" and heat was cut off.
The hydrogen pressure was permitted to drop to about 20 atm. and then
recharged to about 100 atm. The temperature rose to 130ºC. during the
next 40 minutes and about 0.9 mole of hydrogen was absorbed per mole of
turpentine. The heater was then adjusted to maintain this temperature
for about 4 hours to complete the hydrogenaton. Total hydrogen uptake
was about 1 mole per mole of turpentine. Filtration after the reaction
mixture was cooled yielded 1312 grams of crude pinane containing about
30 grams of coconut oil from the catalyst. Distillation of this product
through a short Vigreaux column at atmospheric pressure yielded 1020
grams of pinane boiling below 170º C., n20D = 1.46.5,
= 0.8546, =
- 9.0 (10 cm., neat), which gave only a light yellow color when it was
shaken with 85% sulfuric acid. This represents a yield of about 80%
based on the gum turpentine charged.
The recovered catalyst was
still fully active and was re-used three times to produce yields of 88,
89, and 87% of pinane. The low yield in the first run was due to the
difficulty in removing the last of the pinane from the residual coconut
oil.
Low
Pressure Hydrogenation. Low-pressure hydrogenations were
carried out in stirred autoclaves designed for the hydrogenation of
fats. The largest single charge was a 400-pound drum of gum turpentine.
This hydrogenation was carried out at 22 pounds per square inch gage
and 280º F. for 18.5 hours. At this time the run was stopped because of
servere, leakage at the agitator shaft bearing caused by the action of
hot turpentine on the packing. This hydrogenation was only 84%
complete—that is, quantitative hydrogenation indicated about 0.17 of a
double bond remained per mole of terpene. The original gum turpentine
had about 1.05 double bonds per mole, indicating the presence of 5% of
monocyclic terpenes, which yield p-menthane on hydrogenation. Small
scale runs indicated that substantially complete hydrogenation of gum
turpentine can be attained at 60 pounds per square inch and 150º C.
when a suitable packing is used in the agitator shaft seal.
A portion (2400 grams) of
this crude pinane was distilled through an efficient column at about
50:1 reflux ratio to give about 1500 ml. of pinane containing only
about 1% of residual olefins.
Small and large scale techniques of piNane oxidation are
investigated
Method A. Small samples (2
ml.) of pure pinane were oxidized with oxygen in 50-ml. Erlenmeyer
flasks attached to gas burets. The reaction temperature was controlled
by immersing the reactors in a constant temperature oil bath. The
samples were not stirred. The progress of the reaction was followed by
observing the volume of oxygen absorbed. At the conclusion of each
experiment the peroxide content of the sample was determined.
Method A was used to study
the effect of light on the oxidation of pinane. For runs in the dark,
the reactors were completely covered with tin foil. A 200-watt
incandescent light was used to illuminate the reactors for runs in the
light. The results of these experiments are given in Table I.
Method B. Samples of pinane
(0.1 mole) were oxidized in 125-ml. Erlenmeyer flasks immersed in a
constant temperature oil bath. The samples were stirred by means of a
glass-encased magnetic stirring bar, and wet oxygen from calibrated gas
reservoir was passed over the surface of the liquid at the rate of 1
liter per hour. The exit gas was passed through a Dean-Stark trap and
condenser to remove entrained vapors, and was then collected in a
calibrated gasholder. Samples for use in determining peroxide number
were withdrawn by interrupting the oxidation for a few seconds and
using the oxygen inlet tube as a pipet to withdraw the sample.
Method B was used to
investigate the effect of oxidation temperature on the peroxidation
reaction. The results of these experiments are presented in Figure 1
and in Tables II and III. In calculating the data for Tables II and
III, allowance was made for the moisture content of the oxygen for the
removal of samples, and for the loss through the condenser by
evaporation. Since such calculations involve a number of
approximations, the results are only semiquantitative.
Method C. This method was the
same as Method B except the reactor was simply connected to an oxygen
reservoir and the oxidation was carried out in a closed system. In
Table IV results obtained by this method are compared with those
obtained by method B.
Method D. Oxidations were
made using 100-ml. samples of pinane containing 1.4% of olefins in a
250-ml reactor with a fritted-glass false bottom for introduction of
oxygen and equipped with the usual moisture trap and condenser. A
temperature of 110º C. was maintained by means of a constant
temperature oil bath, and the oxidation time was 6 hours in each case.
The crude oxidates were stripped at 0.3 mm. of mercury pressure to a
pot temperature of 78ºC using water vapor as a carrier gas to remove
unoxidized pinane. Oxygen absorption was not measured, but peroxide
content was determined before and after stripping.
To evaluate the effect of
iron on the peroxidation, duplicate runs were made with and without 1
gram of iron filings in the sample and iron turnings in the head space
and trap. The runs with iron gave light yellow oxidates having peroxide
numbers of 6200 and 6400. Stripping in the presence of iron gave a
product having peroxide number of 10,600. The runs without iron gave
similar oxidates having peroxide numbers of 5800 and 6600; the stripped
product had a peroxide number of 10,800.
Method E. For larger scale
runs (10 to 20 moles) using various grades of pinane, the reactor
consisted of a 3- or 5-liter, three necked flask which was fitted with
an efficient mechanical stirrer, a fritted-glass gas inlet tube, a
thermometer, and a modified Dean-Stark moisture trap and reflux
condenser. The reactor was heated with a heating mantle at the start of
the oxidation and was cooled with an air blast or with a wet cloth
during the latter stages of the reaction. The oxidation was initiated
at 120º to 130º C., and the temperature was lowered as the oxidation
progressed. Samples were removed from time to time and the peroxide
content was determined. Upon completion of the oxidation, the peroxide
was concentrated by stripping off the unreacted pinane under vacuum,
using water vapor as a carrier gas.
Oxygen flow rates of 200 to
400 liters per hour were used, depending on the size of the charge.
Oxygen absorption was not measured directly, but in some experiments an
efficient trap cooled with solid carbon dioxide was used to condense
the volatile material from the exit gas. The amount of oxygen absorbed
was then estimated from the total weight of products recovered. Results
of experiments using this method are given in Tables V, VI, and VII.
The over-all length of the
reactor is about 1 meter. Neck A is fitted with a long-stemmed glass
thermoregulator. The simple regulator shown in Figure 2 is satisfactory
and convenient for this purpose. It is readily set simply by opening
the stopcock until the desired temperature is attained and then closing
it. Necks B and C are used for insertion of a thermocouple well (or
thermometer) and a sampling tube. Neck D is the gas outlet and is
fitted with a Dean-Stark moisture trap and reflux condenser.
The coolant maybe any
suitable high boiling liquid, such as turpentine and is recirculated
through a heat exchanger-reservoir system by means of a centrifugal
pump. The flow is controlled by means of a magnetic valve actuated
through a relay by the thermoregulator. Heat for initiation of the
reaction is provided by wrapping the reactor with electrical heating
tape.
Oxygen input and exhaust were
measured by means of wet test meters. Samples were withdrawn at
suitable intervals for determination of peroxide content. Table VIII
presents data for a typical run by this method.
Cold-Rubber Polymerization.
Samples of a crude pinane oxidate and a pinane hydroperoxide
concentrate were tested by the Government Laboratories of the
University of Akron for use in 5º C. copolymerization of
butadiene-styrene. For this evaluation in amine formula II (Formula A)
and the low sugar iron formula (Formula B) previously reported and a
sugar-free formula (Formula C) were used. The sugar-free formula was
identical with the low-sugar formula except for the omission of the
sugar and part of the pyrophospate from the activator. All peroxides
were tested simultaneously at a given level. Representative data from
these tests are given in Table IX.
Decomposition of Pinane
Hydroperoxide. The general technique used in this work consisted of
weighing a sample of pinane hydroperoxide (Approximately 0.1 gram) into
a small glass ampoule, adding the decomposing agent being tested,
flushing the ampoule thoroughly with nitrogen, and sealing it. The
sealed ampoules were immersed in a constant temperature bath and
removed at suitable intervals, chilled, cleaned thoroughly, and opened.
The sample was transferred to a flask by means of the peroxide number
solvent and the peroxide content was determined. Decomposition
conditions were chosen on the basis of work on the pure peroxide.
Results of these experiments
are given in Tables X, XI, and XII.
Over-all yield of 85% is realized in production of high
purity hydroperoxide
Preparation of Pinane.
Although gum turpentine was used as the starting material in the work
reported, either a- or b pinene can be used. b-pinene hydrogensters
more readily than turpentine or a-pinene and can be hydrogenated at a
little lower temperature. When gum turpentine is used instead of pure
pinenes, the product may contain up to 5% of p-menthane and small
amounts of other saturated terpenes, but these do not interfere in the
oxidation step.
If the hydrogenation step is
carried out properly, the product can be filtered, distilled to remove
the last traces of the catalyst and the carrier, and used for the
production of pinane hydroperoxide without further purification. If the
hydrogenation step is not carried to completion, purification of the
crude pinane may be necessary. As shown in Tables V and X, the presence
of excessive amounts of residual olefins decreases the purity and
stability of the product and the yield of hydroperoxide.
The residual olefins can be
removed by efficient fractional distillation, by washing with
concentrated sulfuric acid or with chromic acid-sulfuric acid mixtures,
by passage through activated silica gel, or by a combination of these
processes. Obviously such methods are relatively time-consuming and
expensive. In some cases it has been found satisfactory to oxidize the
impure pinane for a short time at 130º to 140º C. and recover the
unoxidized pinane by simple distillation. The olefins are more easily,
oxidized than the pinane. As a general rule it is much better to take
adequate precautions to ensure complete hydrogenation than to have to
remove residual olefins from the crude pinane. However, the
hydrogenation conditions should be fairly mild since high temperatures
favor the production of trans-pinane, which is more resistant to
oxidation than is cis-pinane. Furthermore, vigorous hydrogenation
conditions may convect the pinane to monocyclic hydrocarbons.
Sylvestrene and some of its Derivatives
With the discovery of
'sylvestrene' in Swedish pine oil derived from Pinus sylvestris,
probably the most intriguing chapter was opened in the chemistry of
m-menthadienes. We now know for certain that 'sylvestrene' is not a
naturally occurring hydrocarbon but an artifact originating from D3 -
or D4- carene during the process of isolation through the
dihydrochloride. However, during the past one hundred years, the
structures of sylvestrene and its derivatives were the subject of
innumerable inconclusive investigations. In recent times there has been
great interest in the 'sylyestrene' problem and the purpose of this
review is to focus attention on the salient developments in this field.
Sylvestrene
(i)
Structure: Usually 'sylvestrene' is obtained from
sylvestrene dihydrochloride (1) by splitting off two molecules of
hydrogen chloride using aniline sodium acetate and acetic acid or
diethylaniline. Theoretically six m-menthadienes can arise by the
dehydrochlorination process. However, by precise fractionation the
hydrocarbon mixture has been resolved into the isomers designated as
sylvestrene, isosylvestrene and sylveterpinolene with tentative
formulae (II), (III) and (IV) respectively. That formula (II)
represents sylvestrene is firmly established by the n.m.r. analysis of
syivestrene tetrabromide (V) which is obtainable only from sylvestrene.
It was therefore, proposed that the name sylvestrene should be confined
to the D6,8(9) m menthadiene which alone furnishes sylvestrene
tetrabromide.
(ii)
New method of preparation: Whereas the earlier
methods of obtaining sylvestrene depended on the fractionation of the
hydrocarbon mixture derived from sylvestrene dihydrochloride, recently
it was prepared in about 47% yield by heating an ethanol ether solution
of sylvestrene tetrabromide with zine dust. This sylvestrene afforded
copiously the tetrabromide and nitrosochloride derivatives but did not
respond to the acetic anhydride — sulphuric acid colour test.
Sylvestrene nitrosochloride
Wallach who was the first to
prepare the bimolecular sylvestrene nitrosochloride, considered the
monomeric form to be (VI), (VII) or a mixture of the two on the
assumption that sylvestrene was a mixture of (II) and (III). If this
view is accepted, then the dimeric form is either (VIII), (IX), (X) or
a mixture of these. In order to distinguish between these possible
structures. the n.m.r. spectrum of the bimolecular nitrosochloride was
studied. The results obtained favoured the formula (VIII) for the
derivative, which in turn would suggest that the correct formula for
the nomomer is (VI).
Sylvestrene oxide
The epoxidation of
sylvestrene with peracetic acid at temperatures below 0º has resulted
in about 70% yield of sylvestrene oxide (XI). It is a colourless mobile
liquid with a camphor-menthol smell. The physical constants for the
camphor-menthol smell. The physical constants for the purest sample
are: b.p. 90º/20 mm, n29 1.4671, d20 0.9307 and (a) 20D + 54.1º. On
hydration with dilute sulphuric acid it gave the crystalline diol
(XII), m.p. 135º. As will be seen in the sequel, sylvestrene oxide is a
useful raw material for synthesis of oxygenated derivatives in the
m-menthane series.
m-Terpineols
'Sylveterpineol' is the name
given to the unsaturated, optically active tertiary alcohol, which is
obtained as the principal product when sylvestrene dihydrochloride is
shaken with dilute aq. potassium hydroxide. That 'sylveterpineol' is a
mixture of m-menthene-1-ol-8 (XIII) and m-menthene-6-ol-8 (XIV) is
shown by oxidative degradation. The synthesis of these alcohols has
been reported, but physico-chemical data on these compounds are lacking.
With a view to filling up
this gap, 'sylveterpineol' was esterfied with p-nitrobenzoyl chloride
in pyridine medium. By fractional crystallisation of the esters thus
obtained and their subsequent saponification, it was possible to get
pure m-menthen-1-ol-8 (XIII) and m-menthen-6-ol-8 (XIV). The properties
of these alcohols are as follows:
m-menthen-l-ol-8: b.p. 84º/3
mm, 0.9373, 1.4835,
+ 46.20; p-nitrobenzoate, m.p. 66º; phenyl urethane, m.p.
64º.
m-menthen-6-ol-8: b.p. 91º/5
mm, 0.9402, 1.4839,
+ 89.67; p-nitrobenzoate, m.p. 98º; phenyl urethane, m.p.
82º
When sylvestrene oxide was
reduced with lithium aluminium hydride, a mixture of m-menthen-8
(9)-ol-l (XV) and m-menthen-8 (9)-ol-6 (XVI) was obtained. 14 The
separation of these alcohols, by either fractionation or
esterification, was difficult. Therefore, the reaction products were
oxidised with Beckmann's chromic acid mixture. This converted the
secondary alcohol to m-menthen-8(9)-one-6, sylvedihydrocarvone (XVII),
which was then extracted through its semicarbazone; the remaining
tertiary alchol was purified by sublimation.
m-Menthen-8(9)-o1, –1 m.p.
37ºC, +10.1º,
phenyl urethane, m.p. 110º, is a new derivative, and is given the name
b-sylveterpineol. When shaken with conc. hydrochloric acid, it
immediately yielded sylvestrene dihydrochloride, and with 10% sulphuric
acid, it was hydrated to trans-sylveterpin. These two derivatives
confirm the structure of B-sylveterpineol as m-menthen-8(9)-ol-l.
The hydrogenation of
B-sylveterpineol in presence of Raney nickel catalyst led to the
formation of m-menthanol-1 (XVIII), m.p. 35º, + 14.5º. This compound
has not been described in literature.
B-Sylveterpineol undergoes
facile dehydration to hydrocarbons with properties corresponding to a
mixture of sylvestrene and isosylvestrene. Because of this, it was
difficult to prepare the p-nitro- or 3,5-dinitrobenzoate.
Recovery of 3-carene from Chinese
Turpentine and Synthesis of Acetylcarenes
Fractions containing 56~72%
3-carene were recovered by two-stage fractional distillation of Chinese
wood and sulfate turpentines. Acetylation with acetic anhydride using
zinc chloride as catalyst produced a mixture of acetylated carenes with
4-acetyl-2-carene as the main product. The optimal condition for the
acetylation was determined to be: reaction temperature 70ºC, reaction
time 6h, amount of ZnC12 3.8% and the ratio acetic anhydride: 3-carene
2.0:1
Introduction
The monoterpene 3-carene
(3,7,7-trimethyldicyclo 4,1,0-3-hexene) is one of the major components
in wood and sulfate turpentines produced in north China. Its content is
about 10% in this turpentine. 3-Carene also occurs in essential oil,
such as oil from needles and barks of arborvitae (Thuja species).
3-Carene has been used for the synthesis of perfumes and raw materials
for perfumes, for example, 4-acetyl-2- carene and 4-hydroxymethyl-3
carene. However, there is no report about the utilization of 3-carene
in China. The aim of this study was to recover fractions rich in
3-carene from Chinese turpentines and to synthesize 4-acetyl 1-carene.
The synthesis conditions were optimized and the reaction mechanisms
were elucidated.
Distillation of wood and Sulfate Turpentines
Material and Methods
Turpentine samples Wood
turpentine was obtained in March 1987 from the Dunhua wood Rosin
Factory in Dunhua city, Jilin Province, China, using Korean pine (Pinus
koraiensis). Sulfate turpentine was obtained in March 1987 from the
Jiamusi Pulp and Paper Plant in Jiamusi city, Heilongjiang Province,
China, using wood of the following species; 70% Dahurian larch (Larix
dahurica) and 30% of a mixture of Korean pine (P. koraiensis), Yeso
spruce (Picea jezoensis), Khingan fir (Abies nephrole pis).
Fractional distillation the
turpentines were distilled using a silverplated glass column with a
vacuum jacket. The distillation conditions were as follows:
Distillation Results
After the first distillation
a distillate rich in a-pinene was obtained (Table 1). The yield of
a-pinene in the distillate was 82% of the amount in the wood turpentine
and 74% in the case of sulfate turpentine. Practically all 3-carene was
left in the residue.
The residues from the first
distillation were subjected to a second distillation. Two fractions
rich in 3-carene were recovered from the wood turpentine residue (Table
2). The total yield of 3-carene was 74% of that originally present in
the wood turpentine.
The sulfate turpentine reside
yielded a first fraction rich in b-piene, containing 70% of the amount
present in the crude sulfate turpentine, the second distillate was rich
in 3-carene and contained 79% of the original amount in the crude
turpentine.
It was thus possible through
two fractional distillations to recover fractions containing 56~72%
3-carene with a recovery of 74~79% of the 3-carene present in the crude
turpentine.
Synthesis of Acetyl-Carene
Materials and Methods
Synthesis experiments were
carried out with the two carene-rich distillates from the wood
turpentine and the carene-rich one from the sulfate turpentine.
Carene-rich distillate,
acetic acid anhydride and anhydrous zinc chloride were placed in a
three-necked flask equipped with a stirrer, a thermometer, a reflux
condenser and a calcium chloride drying tube. The mixture was kept at a
certain temperature for a certain time under stirring. After the
reaction, water was added and the organic phase was separated. The
aqueous phase was extracted with three portions of diethyl ether. The
ether solutions were combined with the organic phase, the solution was
washed with sodium bicarbonate until free of acid, then dried by
addition of sodium sulfate and the ether was removed. The residue was
vacuum distilled and the fraction recovered in the range 118 ~120ºC at
1333.22Pa containing mainly acetylated carenes was collected.
The synthesis products were
characterized by GC, GC-1R and GC MS. GC-IR spectra were recorded with
a Hewlett-Packard-5890A GC coupled a PRGLIB FTS-60 FTIR instrument
using a HP-5 fused silica capillary column. The GC-MS instrument was a
JEOL-D300 with a SE-30 fused silica capillary column. EI spectra were
recorded at 70 eV.
Results and Discussion
The yield of products is
dependent on the type and the amount of catalyst, the reaction
temperature, the reaction time and the ratio of reactants. Each factor
was investigated and orthogonal experiments were carried out in order
to establish the optimal conditions for the reaction.
Effect of catalyst Tin
tetrachloride (SnC14) and zinc chloride (ZnC12) gave rather similar
catalytic effects. Zinc chloride was preferred because it is less
costly. The optimal amount of zinc chloride is around 3.8%(Table 3).
With higher amounts, polymerization of 3-carene seems to take place.
With lower amounts, the reaction is considerably slowed down.
Effect of temperature. The
yield of acetylated products decreased considerably with increasing
reaction temperature, probably because of polymerization reactions
(Table 4).
Determination of the optimal
reaction conditions. According to the above results and earlier
reports, we decided to study the four factors: reaction temperature,
reaction time, amount of catalyst, ratio of 3-carene and acetic
anhydride in an orthogonal experiment utilizing three levels and nine
experiments, coded L9 (34), (Table 5, 6).
The average yield for every
level of each factor was calculated. Because the yields of products
were nearly the same when the added amounts of catalyst were 2.1% and
3.8% (C1 and C2), the experiments of group A2B1C1D3 and A2B1C2D3 were
repeated, and compared with the highest yield of Table 6.
Under A2B1C2D3 conditions,
the yield of products was the highest and identical to the conditions
and results of No.4 experiment (Table 7). So the optimal conditions
were: reaction temperature 70ºC, reaction time 6h, added amount of
catalyst 3.8%, acetic acid anhydride 3-carene 2.0:1. Under these
conditions, the yield of products was 74~75%.
Homopolymers and Copolymers of Acrylates
Introduction
In continuation of the
studies on the preparation of polymers containing terpenes and various
terpene derivatives, two new derivatives from a-pinine have been
investigated: (1) homoterpenylmethyl carbinol, 6-hydroxy-2-
(1-hydroxy-1-methylethyl) heptanoic acid g-lactone (I), and (2)
a-campholenol, 2-(2,2,3-trimethyl-3cyclopentenyl) ethylalcohol (II). I
was prepared by Howell and Hedrick by the platinum oxide reduction of
homoterpenylmethyl ketone in sodium hydroxide solution; H was obtained
by reduction of the corresponding aldehyde, a-campholene aldehyde. The
properties and reactions of II and a-campholene aldehyde have been
deseribed. Synthesis of various esters of II, conversion of the esters
to epoxides, and evaluation of the epoxides as plasticizer-stabilizers
for poly (vinyl chloride) have also been described.
The work here describes the
preparation and polymerization of the acrylates and methacrylates of I
and II. In addition, studies on the epoxidation, curing, and hydrolysis
of some of the polymers of II were conducted. Polymers containing the
unit I would be expected to undergo the lactone ring opening to yield
water-soluble polymers. Polymers of II would be expected to undergo an
epoxidation readily. The reaction products of epoxidized polymers with,
for example, fatty acids could find applications in the coatings field.
Results and Discussion
Monomers
Samples of a-campholene
aldehyde, I and II, were provided by Dr. G.W. Hedrick of the Naval
Stores Laboratory of the Southern Utilization Research and Development
Divisions, Agricultural Research Service. In the preparation of
additional II, a-campholene aldehyde was reduced with lithium aluminum
hydride. The physical constants of the three materials are given in
Table 1.
The acrylates and
methacrylates of II and I were prepared according to the procedure of
Marvel and Schwen. However, instead of distilling the products,
chromatography on silicic acid with diethyl ether-hexane mixtures as
eluent was used for purification of the monomers. Physical
characteristics of the monomers and their analytical data are given in
Table 2. Infrared analysis showed the presence of a trace of
hydroxyl-containing material in the acrylate and methacrylate of I.
Although there was a good agreement in analytical data between the
calculated and experimental values, it is possible that a minor amount
of the hydrolyzed lactone was still present in the derivatives of I or
the hydroxyl band may have been due to absorbed moisture. The residue
found in the analysis of the methacrylate of II was probably due to
colloidal silicic acid introduced inadvertently during the
chromatography of the monomer.
Homopolymerization
The experimental conditions
and polymerization results for the various polymers are given in Table
3.
Hompolymerizations were
conducted in an emulsion system with the use of a detergent (Siponate
DS-10) rather than soap as the emulsifier. The detergent gave better
latices and conversions. The low inherent viscosities for the
homopolymers of methacrylate of I and acrylate of II were unexpected.
The polymers were isolated as white powders, which could be molded (at
about 150ºC) into water-clear, brittle films. On one occasion the
acrylate of I gave a material, which could be molded into a strong
film. In the homopolymerization of the acrylate of II, whenever the
conversion exceeded 35%, some insoluble polymer began to form.
Similarly, long drying periods insolubilized the material, probably by
oxidative coupling at the allylic position. The polyacrylates of I were
soluble in ethyl methyl ketone and chloroform. The polyacrylates of II
were soluble in tetrahydrofuran, ethylmethyl ketone, and methylene
chloride. Whereas only a trace of a hydroxyl-containing material was
indicated in the acrylate and methacrylate of I monomers the
corresponding homopolymers appeared to contain more of the hydroxy acid
despite the fact that their analytical data agreed with the calculated.
A tightly bound water of hydration cannot be ruled out, as the infrared
analysis is not conclusive on this point.
Copolymerization
Copolymers of the acrylate of
I. The acrylate of I was copolymerized with the acrylate and
methacrylate of II, and with acrylonitrile. The acrylate copolymers
were isolated as white, hard solids, soluble in ethyl methyl ketone,
whereas the acrylonitrile copolymer was a yellow solid, soluble in
N-methylphrrolidone. The acrylate copolymers had inherent viscosities
below 1.0; acrylonitrile copolymer had the exceptionally high viscosity
of 4.4. The acrylates could be molded (at about 150ºC.) into
water-clear, brittle films, whereas the acrylonitrile copolymer gave an
extremely tough, somewhat soft film.
The properties of all the
copolymer films are given in Table 4. All of the copolymers gave
transparent films.
Prolonged drying of the
copolymers of the acrylate and methacrylate of II insolubilized them.
In genera, the copolymers of acrylate of I exhibited adhesion to a
copper foil in varying degrees. This may have been due to the hydroxy
acid component present in the polymers.
Copolymers of the
methacrylate of I. The methacrylate
and acrylate copolymers were isolate as white, hard solids soluble in
ethyl methyl ketone; the acrylonitrile copolymer was a yellow soild,
soluble in N-methylpyrrolidone. None of the methacrylate of I
copolymers possessed adhesive properties.
Copolymers of the acrylate
and methacrylate of II. The acrylate/acrylonitrile copolymer was
isolated as a yellow solid in a 95% yield of which only 30% was soluble
in N-methylpyrrolidone. The insolubility was probably due to the
corsslinking of the acrylate portion.
The
methacrylate/acrylonitrile copolymer was isolated in a quantitative
yield; however, only about 20% of it was soluble in N-methylpyrrolidone.
The solution
methacrylate/fumaronitrile copolymer was isolated as a dark tan solid,
soluble in tetrahydrofuran.
Terpolymerization
Terpolymers of the acrylate
of I. Two series of terpolymers involving the acrylate of I have been
prepared. One of the series involved BD/AN comonomers. The terpolymers
were isolated as water-clear to white rubbery masses, which could be
molded (at about 130ºC.) into clear tough films. Whereas the 30/61/9
acrylate BD/AN terpolymer was essentially insoluble in hot
tetrahydrofuran and chloroform, only 10% of the 60/33/7 acrylate BD/AN
terpolymer was not soluble and the 78/17/5 acrylate/BD/AN terpolymer
was soluble in chloroform and tetrahydrofuran.
The other series involved
BD/Sty comonomers. These materials again were isolated as water-clear
to white rubbery masses, which could be molded (at about 130ºC.) into
clear, tough films. A film prepared on copper foil of the 80/14/6
acrylate/BD/Sty terpolymer adhered strongly to the foil. Of the four
compositions only the 80/14/6 and 66/24/10 acrylate/BD/Sty terpolymers
were partially (~70%) soluble in hot ethyl methyl ketone.
Terpolymers of the acrylate
of II. Another terpolymer series identical to the one described but
with the acrylate of II was attempted. However, with both, the BD/AN
and BD/Sty comonomers only low conversions were realized. The best
yield (33%) was obtained with the 75/20/5 acrylate BD/AN terpolymer.
The two terpolymers, 75/20/5 and 58/34/8, on which inherent viscosities
were run, were soluble in tetra-hydrofuran and had good viscosity
values. The films pressed (at about 130ºC.) from these materials were
clear, rubbery, and strong.
Epoxidation
Epoxidation of several
polymers was explored to increase their functionality. Development of
adhesive properties was also sought. The following polymers were
investigated: (1) polyacrylate of II, (2) 60/40 acrylate of I/acrylate
of II copolymer, and (3) 66/24/10 acrylate of I/BD/Sty terpolymer. The
in-situ method11 with hydrogen peroxide/glacial acetic acid with a
resin catalyst (Amerlite IR-120) was explored. This method was
preferred over the ones involving use of preformed peracids because it
gave higher oxirane oxygen content in a shorter time and less
contamination in the final product. Ethyl methyl ketone was used as a
solvent for the polymers. Normally, in epoxidations of polymers,
secondary reactions products, such as glycol derivatives, ketones and
ether derivatives, would be expected.
According to the infrared
analysis of the epoxidized materials, only a trace amount of
unsaturation was observed in the epoxidized homopolymer of acrylate of
II and no unsaturation was detected in the other two materials.
Furthermore, absorption bands attributed to epoxides (1250, 840 cm.-1)
were observed in the epoxidized polymers.
Analytical data, calculated
on the basis of one oxygen atom addition across the double bond,
indicated that for the polyacrylate of II only 10% of the theoretical
addition had taken place, for the copolymer 38%, and for the terpolymer
25%. A more accurate determination could be probably achieved by the
ether-HCI method.
Although the epoxidized
copolymer was isolated as a soluble product from the reaction mixture,
drying it at 39ºC. for 26 hr. insolubilized it completely.
In the epoxidation of the
terpolyemr (66/24/10 acrylate of I/BD/Sty), two products were produced
in about equal amounts. One of the materials was water-soluble, the
other was water-insoluble. The water-soluble material was also
insoluble in hot ethyl methyl ketone, was extremely tough, and a good
film could not be molded. Hence an infrared spectrum could not be
obtained. The water-soluble material was pressed into a film; the
infrared spectrum showed it to be the hydroxy acid and contained
absorption bands characteristic of epoxides. Analytical data on the
water-soluble material could also be accounted for by assuming opening
of the lactone ring. It is surprising that the lactone ring was opened
under these acidic conditions.
Curing
Epoxypolybutadienes cured
with polyamines or anhydrides are good adhesives to metallic
substrates. Accordingly, the epoxidized polyacrylate of II and the
acrylate of I/acrylate of II copolymer were mixed with
p-phenylenediamine, placed between copper foils, and compressed and
heated at 160ºC. for 2 min. The film from the polyacrylate of II was
extremely hard and completely nonadhesive; the copolymer film was
partially adhesive.
Hydrolysis of Polymethacrylate of I
The lactone ring in polymers
of I should be susceptible to basic hydrolysis. A sample of the
methacrylate homopolymer was hydrolyzed with 3.5% ethanolic potassium
hydroxide at room temperature. After a period of about 2 hr. the
infrared spectrum showed that most of the lactone ring had been opened;
the product was soluble in ethanol and water. In water the hydrolyzed
polymer formed a light blue, very viscous solution. Evaporation of
water yielded a transparent, strong film. Infrared analysis on the film
showed the presence of a strong absorption band for the carboxylate
anion at 1565 and 1390 cm.-1 and only a minor absorption band at 1775
cm.-1, indicative of the lactone carbonyl. Thus, the potassium
hydroxide-treated polymer is essentially all potassium salt of the
polycarboxylate. The extremely facile opening of the lactone ring
suggests an easy preparation of water-soluble polymers.
Polymers and Copolymers of Vinyl
Pinolate
Preparation of Vinyl Pinolate
The preparation of vinyl
pinolate from pinolic acid has been described previously. More recent
work has shown that the product formed from the reaction of pinolic
acid, vinyl acetate, and mercuric sulfate is probably an acetoxyacetal,
which can be hydrolyzed at room temperature with mineral acid. Infrared
absorption for a hydroxyl group was completely absent in the
unhydrolyzed product. Hydrolysis, however, gave the expected vinyl
pinolate.
Polymerization
Polymerization of vinly
pinolate has been accomplished by free radical initiation in bulk,
solution, suspension and emulsion systems. The conditions for
polymerization and some properties of the samples of poly (vinyl
pinolate) are summarized in Table I. Preparation of poly (vinyl
pinolate) in suspension was unsuccessful until neutral buffered
solution was substituted for distilled water in the polymerization
recipe. In contrast, polymerization of vinyl pinolate in buffered and
unbuffered emulsion systems produced the same results.
All the samples of poly
(vinyl pinolate) are colorless, glasslike solids that melt between 70
and 105ºC. Except for sample 31-B which is poly (vinyl pinolate)
prepared in emulsion, the samples are soluble in methanol, acetone, and
tetrahydrofuran, slightly soluble in benzene and insoluble in petroluem
ether. Sample 31-B is soluble in acetone and tetrahydrofuran until it
is dried. Then it is insoluble in acetone, tetrahydrofuran and several
other solvents.
Because poly (vinly pinolate)
contains one hydroxyl group per repeating unit, reaction with a
diisocyanate would be expected to produce a high degree of
crosslinking. To prepare low molecular weight polymers that contain
relatively fewer hydroxyl groups than poly (vinly pinolate) and might
therefore be more suitable for extending with diisocyanates, vinyl
pinolate was copolymerized in solution with vinyl acetate and vinyl
chloride. Table II contains information concerning the preparation and
properties of several vinyl pinolate-vinyl acetate copolymers and Table
III vinyl pinolate-vinyl chloride copolymers. Transparent, colorless
films can be cast from both vinyl pinolate-vinyl chloride copolymers.
Transparent, colorless films can be cast from both vinyl pinolate-vinyl
acetate and vinyl pinolate vinyl chloride copolymers, but the films are
brittle indicating that the vinyl pinolate units do not produce any
appreciable internal plasticization.
Vinyl pinolate was
copolymerized with vinyl acetate and vinyl chloride in emulsion as well
as in solution. The data resulting from the copolymerization
experiments are compiled in Table IV.
Poly (vinyl acetate) and poly
(vinyl chloride) prepared in emulsion are soluble in acetone and
tetrahydrofuran and so are the copolymers of vinyl pinolate prepared in
solution and listed in Tables II and III. In contrast, the copolymers
of vinyl pinolate with vinyl acetate and vinyl chloride prepared in
emulsion are soluble in acetone and
tetrahydrofuran only until they are dried at room temperature. Attempts
to dissolve the dried co-polymer in benzene, acetone, tetrahydrofuran,
and dimethyl sulfoxide resulted in the slow softening and swelling of
the copolymer. Apparently even small amounts of vinyl pinolate, as
small as 0.5 mole % copolymerized in emulsion with vinyl acetate or
vinyl chloride produce a marked decrease in the solution of the dried
copolymer.
Vinyl pinolate fails to
copolymerize with vinylidene chloride under the emulsion polymerization
conditions. Under similar conditions, the relative reactivity ratios of
vinylidene chloride (0.08) and the vinyl ester of a long chain fatty
acid, e.g., vinyl stearate (3.80), were determined and are unfavorable
for copolymerization.
Reaction of vinyl pinolate copolymers with Isocyanates
To learn something of the
reactions of vinyl pinolate and its vinyl chloride and vinyl acetate
copolymers with isocyanates, a method was used based upon spectral
analyses. By determining infrared absorbancies of a stretching
vibration arising from the isocyanate group at 4.5µ of solutions of
vinyl pinolate and its copolymers reacted with toluene diisocyanate and
phenyl isocyanate it was possible to estimate the decrease in
isocyanate concentration caused by the reaction. The change in
concentration as represented by change in absorbancy gave a convenient
method for measuring reactivity. Poly (viny acetate) and poly (viny
chloride) homopolymers exhibited little or no reaction with either
isocyanate at 75ºC. (Table VI). One of the isocyanate groups of toluene
diisocyanate was less reactive than the other group, since almost half
the isocyanate was unreacted when equivalent quantities of vinyl
pinolate and the isocyanate were reacted. Phenyl isocyanate reacted
completely. Similar results were obtained with the vinyl acetate-vinyl
pinolate copolymer, 123-A. Copolymers, 44-2 and a mixture of
121-A-123-A, from which excess toluene diisocyanate was removed after
reaction by precipitating and washing with hexane contained free
isocyanate groups. With 0.1N solutions of the copolymers, based on
vinyl pinolate content, the residual isocyanate content was 0.07N for
the vinyl chloride copolymer and 0.064 for the vinyl acetate copolymer.
The results of a rate study
involving reactions of the copolymers 44-2 and 123-A and phenyl
isocyanate are tabulated in Table V. After about 6 hr., the isocyanate
concentration with both polymers was about 0.07N (calculated 0.07N) and
did not change much after an additional 8 hr. heating.
Experimental
Preparation of Vinyl Pinolate
Pinolic acid, 372 g. (2.0
moles), freshly distilled vinyl acetate, 2200 ml., copper resinate, 1.0
g., and mercuric acetate, 8.0 g., were mixed in a 3-1 flask.
Concentrated sulfuric acid, 1.0 ml., was added and agitation continued
at 0-5ºC. until the pinolic acid was in solution. The batch was stored
in a refrigerator (10ºC.) for two days. The sulfuric acid was
neutralized with sodium acetate and the excess vinyl acetate and acetic
acid distilled below 30ºC. The residue was dissolved in 1500 ml. ether
and washed with vigorous agitation for 15 min. with three 500-ml.
portions of 1.5N hydrochloric acid. The solution was washed at 10ºC.
with cold water, cold 0.5N sodium carbonate and dried. The ether was
removed and the product distilled bulb to bulb; b.p. 106ºC./1.0 mm.;
334 g., 81%. The crude ester was redistilled through a column packed
with glass helices, b.p. 84ºC. /0.2 mm., 1.4656.
Polymerization of Vinyl Pinolate in Solution
A 250-ml., three-necked flask
equipped with a spiral condenser, thermometer, magnetic stirring bar,
and nitrogen inlet tube was charged with vinyl pinolate,
azobisisobutyronitrile (2% of weight of the monomer), and 150 ml. of
A.R. grade benzene. The solution was stirred at reflux temperature
under nitrogen for the desired number of hours. Then the benzene was
removed by aspiration and the polymer was purified by repeatedly
dissolving it in acetone and precipitating it in petroleum ether
(35-75ºC.). Finally the polymer was dissolved in benzene and
freezedried.
Polymerization of Vinyl Pinolate in Suspension
Into a 100-ml., two-necked
flask fitted with a spiral condenser, magnetic stirring bar, and
nitrogen inlet tube was placed 3.0 g. of vinyl pinolate, 0.03 g. of
Duponol C (du Pont's sodium lauryl sulfate), 0.3 g. of
azobisisobutyronitrile, and 10 ml. of neutral buffered solution. The
suspension was stirred under nitrogen at 60ºC. for 48 hr. The poly
(vinyl pinolate), which had coalesced into a single lump, was dissolved
in acetone and precipitiated first in water and then in petroleum
ether. Then the polymer was dried at 60ºC. in a vacuum oven at 20 mm.
of mercury.
Polymerization of Vinyl Pinolate in Emulsion
A 2-oz., screw-capped bottle
was charged with 0.3 g., of Triton X-301 (Rohm and Haas, sodium
alkylaryl polyether sulfate, 20% aqueous disperision), 1.5 g. of vinyl
pinolate, 0.75ml of 25% aqueous potassium persulfate, and 3 ml. of
distilled water. After the air had been flushed from the bottle with a
stream of nitrogen the bottle was capped and tumbled in a water bath at
60ºC. for 48 hr. A sulfuric acid-salt solution (5% H2SO4 saturated with
salt) was used to break the emulsion. The poly (vinylpinolate) was
washed with water and purified by the same procedure described for
suspension polymerization. After it has been dried, the poly (vinyl
pinolate) was insoluble in dimethylformamide, methanol, acetone,
2-butanone, tetrahydrofuran, dioxane benzene, toluene, chloroform, and
carbon tetrachloride.
Copolymerization of Vinyl Pinolate and Vinyl Acetate in
Solution
The same procedure described
for solution polymerization of vinyl pinolate was used with the
exception that a calculated amount of freshly distilled vinyl acetate
was added to the solution.
Copolymerization of Vinyl Pinolate and Vinyl Chloride in
Solution
Polymerization bottles
(110-ml., Ace Glass T 1506) were charged with calculated amounts of
vinyl pinolate, 0.2 g. of azobisisobutyronitrile, 40 ml. of A.R. grade
benzene and then cooled in a Dry Ice-acetone bath. Vinyl chloride was
condensed in the bottles until slight excess was present. Went the
excess vinyl chloride had been allowed to evaporate, the bottles were
sealed with crown-type bottle caps and tumbled in a water bath at 60ºC.
for 48 hr. The copolymers were coagulated by pouring the benzene
solutions into 400 ml. of methanol and purified by repeatedly
dissolving them in tetrahydrofuran and precipitating them in rapidly
agitated methanol. After the copolymers had been dried at room
temperature for 48 hr. they could be dissolved easily in acetone and
tetrahydrofuran but only with difficulty in benzene.
Copolymerization of Vinyl Pinolate and Vinyl Chloride in
Emulsion
The calculated amounts of
vinyl pinolate, 40 ml. of oxygen-freewater 3.0 g. of Triton X-301, and
4 ml. of 2.5% potassium persulfate solution were placed into 110- ml.
polymerizaton bottles. While the bottles were being cooled in a Dry
Ice-acetone bath a slight excess of vinyl chloride was condensed into
it. When the excess had been allowed to evaporate the bottles were
capped and tumbled at 50ºC. for 72 hr. The copolymers were coagulated
with 400 ml. of saturated salt solution and collected on filter paper.
After being washed with water and then with methanol, the copolymers
were repeatedly dissolved in tetrahydrofuran and precipitated in
methanol. Finally, the copolymers were dried at room temperature for 48
hr. If the copolymers are overheated, on drying they become insoluble
in acetone, tetrahydrofuran, dimethyl sulfoxide, dimethyl formamide,
and benzene.
Reaction of Polymers with Isocyanates
Exploratory experiments were
made to select a solvent and to determine a suitable temperature and
time for running the reactions. Tetrahydrofuran was a good solvent for
the polymer; however, the isocyanates, toluene diisocyanate (a mixture
of 2,4 and 2,6-isomers in a 4:1 ratio) and phenyl isocyanate were not
stable in this solvent at 75ºC. since this solvent did not affect the
isocyanate adversely.
In instances indicated, the
benzene was replaced with tetrahydrofuran for reasons of solubility.
The benzene was removed in vacuo at room temperature and the residual
polymer dissolved in the tetrahydrofuran. In other instances also, as
indicated, the polymers crosslinked and became insoluble in the latter
solvent.
The substances investigated are
tabulated in Table VI.
Benzene solutions (0.1N with
respect to vinyl pinolate) of each of the copolymers 123-A and 44-2
were made up containing 0.3N phenyl isocyanate. These were heated to
75ºC. for periods of 1, 2, 4, 6, and 14 hr. After each heating period
1-ml. samples were removed and diluted with 2 ml. of tetrahydrofuran.
The results are tabulated in Table V. The concentration of the hydroxyl
and isocyanate initially in the diluted samples were about 0.03 and
0.1N, respectively.
In another experiment,
benzene solutions containing 0.93 g. (0.1N) of a mixture of copolymers
121-A and 123-A in equal amounts, and 0.87 g. (1.0N) toluene
diisocyanate diluted to 10 ml were heated to 75ºC for 2 hr. The
polymers were precipitated by pouring into hexane, washed by
decantation, redissolved and reprecipitated to remove excess
isocyanate. The polymers were dissolved in tetrahydrofuran and diluted
to 10 ml. The isocyanate concentrations after removal of excess
isocyanate were 0.064N for the 121-A-123-A polymer mixture and 0.07N
for the 44-2 polymer.
Homopolymerization of Hydronopyl Vinyl
Ether
Discussion
The work reported in this
paper was undertaken to determine the optimum conditions for
polymerizing hydronopyl vinyl ether (Ia) and 2-hydronopoxyethyl vinyl
ether (Ib) and to investigate the properties of the resulting polymers.
Samples of hydronoply vinyl
ether (HVE) and 2-hydronopoxyethyl-vinyl ether (HEVE) were provided by
the Naval Stores Division of the Southern Utilization Research and
Development Division of the Agricultural Research Service and were
prepared by published methods. During the course of the investigation,
the preparation of additional HEVE became necessary. Bissel reported a
yield of 38% (based on sodium) for the preparation of HEVE. He allowed
sodium to react with a large excess of hydronopol and then treated the
resulting suspension with 2-chloroethyl-vinyl ether. We have found that
HEVE can be prepared in 93% yield (based on hydronopol) by mixing
hydronopol and sodium hydride in an excess of 2-chloroethyl-vinyl ether.
The polymerization of HVE and
HEVE by initiation with free radical, cationic, and coordination
catalysts was investigated. In accord with the report that most vinyl
ethers do not polymerize well by free radical initiation, neither HVE
nor HEVE polymerized appreciably by free radical initiation in bulk or
emulsion systems.
Under the conditions studied,
the order of effectiveness of cationic initiation of the polymerization
of HVE is stannic chloride >boron fluoride etherate >
titanium tetrachloride > vanadium oxychloride. Vanadium
trichloride does not catalyze the polymerization of HVE. For
polymerization of HEVE the order of effectiveness is boron fluoride
etherate >>> stannic chloride. Titanium
tetrachloride, vanadium oxychloride, and vanadium trichloride do not
catalyze the polymerization.
Polymerization of HEVE by
initiation with boron fluoride etherate at —78ºC. produces the highest
conversion and molecular weight of any method investigated. The poly
(HEVE) is a tough, slightly tacky rubber with a specific rotation of = - 20.1º. It is soluble
in petroleum ether, benzene, toluene, carbon tetrachloride, and
tetrahydrofuran but insoluble in methanol, acetone, and 2-butanone.
Okamura and Higashimura
report that poly (isobutyl vinyl ether) can be separated into
crystalline and noncrystalline fractions because the crystalline
fraction is less soluble in 2-butanone. The insolubility of poly (HEVE)
in 2-butanone may indicate the presence of some crystalline portions.
At best, coordination
catalysts prepared by mixing triisobutylaluminum with titanium
tetrachloride or vanadium oxychloride or vanadium trichloride produce
poor yields of poly (HEVE). Poor results were also obtained when
attempts were made to polymerize HVE with catalysts prepared by mixing
triisobutylaluminum with vanadium oxychloride or vanadium trichloride.
Conversely, catalyst prepared by mixing triisobutylaluminum and
titanium tetrachloride in a mole ratio of 2.7:1 produces poly (HVE) in
the highest conversion and with the highest molecular weight of any
catalyst investigated by us.
The poly (HVE) prepared with
triisobutylaluminum-titanium tetrachloride catalyst is hard and
brittle, but becomes rubbery at temperatures above 45ºC. It has a
specific rotation of =
- 26.2 and is soluble and insoluble in the same solvents as poly
(HEVE). An x-ray diffraction pattern indicates considerable
crystallinity in this polymer.
Experimental
Materials
Hydronopyl vinyl ether (HVE),
b.p. 80-81ºC./2 mm., 1.4788; —2.3.8º (0.3882 g. in 25
ml. of benzene); 2-hydronopoxyethyl vinyl ether (HEVE), b.p..
87-88ºC./0.5 mm., 1.4760,
— 18.1º (0.418 g. in 25 ml of benzene), and hydronopol, b.p.
126-128ºC./10 mm., 1.488
were provided by the USDA Naval Stores Laboratory, Olustee, Florida.
The vinyl ethers contained 0.2% of hydroquinone and were purified by
the method described by Schildknecht, Zosc, and McKinley and passed
through alumina (Merck's chromatographic grade) just before they were
used. 2-Chloroethyl-vinyl ether was obtained from Monomer-Polymer
Laboratories and distilled before use. Hexane (Phillips 99%) was
reluxed over sulfuric acid, washed, dried with potassium carbonate, and
distilled from over sodium. A dispersion of sodium hydride (50.6% by
weight) in mineral oil was procured from Metal Hydrides, Inc. The boron
fluoride etherate was obtained from Eastman Organic Chemicals, stannic
chloride from Baker Chemical Company triisobutylaluminum from Texas
Alkyls, titanium tetrachloride (99.5%) from Matheson, Coleman, and
Bell, and vanadium trichloride and vanadium oxychloride from Anderson
Chemical Company.
Preparation of 2-Hydronopoxyethyl Vinyl Ether
Into a 5-liter four-necked
flask fitted with a stirrer, reflux condenser that was protected with a
calcium chloride drying tube, addition funnel, and nitrogen inlet tube
were placed 321 g. (6.68 moles) of NaH in mineral oil (50.6% dispersion
by weight) and 650 g. (6.1 moles) of 2-chloroethyl vinyl ether. While
the mixture was stirred rapidly, 460 g. (2.7 moles) of hydronopol was
added over a period of 1 hr. Stirring was continued for 2 hr. at room
temperature and for 48 hours at reflux temperature. The reaction
mixture was allowed to cool to room temperature and 500 ml. of methanol
followed by 1500 ml. of water was added slowly. Six 250-ml. portions of
ether were used to extract the organic material. The portions were
combined, washed with 500 ml. of water, and dried over anyhydrous
magnesium sulfate. The ether and methanol were removed by distillation
and the residue was distilled under reduced pressure through a 100 × 1
cm. spinning band column. A total of 580 g. (93% yield based on
hydronopol) of 2-hydronopoxy-ethyl vinyl ether, b.p. 109ºC./0.75 mm., 1.4730, was collected.
Polymerization of HVE and HEVE
Attempted free radical
initiation in bulk. A 6 × 1 in. polymerization tube was charged with
2.0 g. of HVE and 0.02 g. of a, a’-azodiisobutyronitrile. To purge the
reaction mixture of oxygen the pressure in the tube was reduced to 0.1
mm. Hg with a vacuum pump, and then nitrogen was admitted to the tube.
Then the pressure was reduced to 0.1 mm. Hg and the tube was sealed and
heated in an oil bath at 65ºC. At the end of 40 hr. the contents of the
tube was a thin liquid that was completely soluble in methanol. Similar
results were obtained when 2.0 g. of HEVE was substituted for HVE.
Attempted free radical
initiation in emulsion. Into a 2-oz. screwtopped bottle were placed 0.2
g. of Triton X-301 (a 20% aqueous dispersion of Rohm and Haas sodium
alkylarly polyether sulfate), 1.0 g of HVE, 5 ml. of distilled water,
and 0.5 ml. of 2.5% potassium persulfate solution. The bottle was
flushed with nitrogen, capped, and tumbled in a water bath at 55ºC. for
36 hr. After the emulsion had been broken with saturated sodium
chloride solution, two layers formed. The organic layer was a free
flowing liquid completely soluble in methanol. The same results were
obtained when 2.0 g. of HEVE was substituted for HVE.
Initiation with boron
fluoride etherate. A method similar to the one reported by Sorenson and
Campbell6 was used. A 250-ml., three-necked flask was fitted with a
stirrer, nitrogen inlet tube, and rubber, serum-bottle cap and charged
with 10 g. of vinyl ether in 40-ml.of n-hexane. While the solution was
kept under a nitrogen atmosphere and stirred, it was cooled in Dry
Ice-acetone to -78ºC. A hypodermic needle was inserted through the
serum cap and four drops of boron fluoride etherate were added to the
solution. After 30 min. another four drops were added and the mixture
was stirred for the desired length of time. A 10-ml. portion of
methanol was poured into the reaction mixture, which was allowed to
warm to room temperature. The resulting solution was poured into 800ml.
of methanol that was being rapidly stirred. The polymer that
precipitated was removed from the supernatant liquid. Further
purification of the polymer was effected by dissolving it in benzene
and repeating the precipitation step. Finally the polymer was dissolved
in 200 ml. of benzene. The solution was filtered and the polymer
isolated by freeze-drying. Inherent viscosities were calculated from
flow times of the benzene solution taken at 30ºC. in a number 50
Cannon-Fenske viscometer. Data for polymerization of HVE and HEVE are
collected in Tables I and II.
Initiation with boron
fluoride etherate (Flash polymerization). Into a 250-ml., four-necked
flask fitted a stirrer, nitrogen inlet tube, Dry Iceacetone cooled
dropping funnel and Dry Ice-acetone cooled condenser was placed 30 ml.
of n-hexane and eight drops of boron fluoride etherate. While a
nitrogen atmosphere was maintained, the solution was cooled to —78ºC.
and a solution of 10 g. of vinyl ether in 20 ml. of n-hexane that was
also at —78ºC. was added rapidly. After the reaction mixture had been
stirred for 30 min., 10 ml. of methanol was added and the resulting
solution was allowed to warm to room temperature. The poly (vinyl
ether) was purified and isolated by the same method described in the
preceding section. Data for the polymerization of HVE and HEVE are
collected in Tables I and II.
Initiation with stannic
chloride, titanium tetrachloride and vanadium oxychloride. Inside a dry
box that was continually flushed with nitrogen, a 4-oz. screw-topped
bottle was charged with a weighed amount of vinyl ether and 15 ml. of
n-hexane. The bottle was sealed with a screw cap that had a hole
punched in it and had been lined with a neoprene gasket. When the
bottle had been cooled to the desired temperature, a measured volume of
n-hexane solution containing a known amount of metal chloride or
oxychloride was injected through the gasket into the bottle. Cooling
was continued until polymerization was terminated by addition of 10 ml.
of methanol. The poly(vinyl ether) was purified by the same method
described previously. Data concerning the polymerization of HVE and
HEVE with cationic initiators are collected in Tables I and II.
Attempted initiation with
vanadium trichloride. In general the procedure was the same as
described in the preceding section, although the order in which the
reagents were added was different. The vanadium trichloride was weighed
directly into the polymerization bottle and mixed with n-hexane. Then
after the bottle was sealed and cooled, the vinyl ether was injected
into the bottle. Tables I and II contain data for the attempted
polymerization of HVE and HEVE with vanadium trichloride.
Initiation with "Coordination
Type" catalysts. A 4-oz. screw-topped bottle was charged, in a dry box
and under nitrogen, with hexane (10 ml./g. monomer), a measured volume
of a hexane solution of triisobutylaluminum (0.1. g. i-Bu3Al/ml.) and a
measured volume of hexane solution of titanium tetrachloride (0.084 g.
TiCl4/ml.) or vanadium oxychloride (0.03 g. VOCl3/ml.) or a weighed
amount of vanadium trichloride. The bottle was sealed with a
neoprene-gasketed cap and the catalyst mixture was allowed to age.
If the polymerization were to
be performed at room temperature, a measured volume of vinyl ether was
injected into the polymerization bottle, which was shaken occasionally
while it stood for 24 hr. For polymerization at —78ºC. the catalyst
mixture, after aging, was cooled in a Dry Ice-acetone bath for 30 min.
and a measured volume of vinyl ether was injected slowly into the
bottle. Cooling was maintained for 24 hr., during which time the
reaction mixture was swirled occasionally. Then the contents of the
bottle were poured into rapidly stirred methanol. The precipitated
polymer was purified by the same method previously described. Data for
the polymerization of HVE and HEVE are collected in Tables III-V.
X-Ray Analysis of Poly (HVE)
A thick film was obtained by
repeated casting of thin layers of a benzene solution of the poly
(HVE). After the portions had dried over water, the film was removed
from the water and allowed to remain at room temperature for two weeks
to remove residual solvent.
A Phillips x-ray diffraction
instrument (operated by Dr. M.L. Corrin) was used. The major machine
settings were: 35 Kv., 20 ma., B1 200, SF 16, TC 4, and M 0.8.
The scan of diffracted x-rays (Fig.
1) indicates two maxima (2q = 13.5 and 19.0). Using l = 1.54 and
Bragg's Law q = 2d sin the spacing distances are 6.55 and 4.66 A. The
sharpness of the recorded scan and the short distance (d) indicate
considerable crystalline polymer structure.
Evaluation of Poly (HEVE)
Preparation of sample. A
150-g. sample for evaluation was prepared by polymerizing 10-30-g. lots
of 2-hydronopoxyethyl-vinyl ether in dry n-hexane solution by boron
fluoride initiation in a Dry Ice-acetone cooling bath. The
polymerization mixture was stirred for the first 4 hr. and then allowed
to stand for 14 hr. Then, methanol was added, the mixture stirred well
and then allowed to warm to room temperature. The polymer was dissolved
in benzene, the solution was filtered, and then the polymer
precipitated by adding this solution to excess methanol with stirring.
Solution in benzene and reprecipitation in methanol was repeated two
more times and then the polymer was dried under reduced pressure. On
the average conversion was 96% and the inherent viscosity of the
polymer varied from 1.5 to 2.1 with the average for the 150-g. sample
being 1.8.
Terpolymers of Ethylene and Propylene
with d-Limonene and b-Pinene
Introduction
Ethylene-propylene
terpolymers (EPT) have recently enjoyed a great deal of research
activity due to their remarkable oxidation and ozone resistance and
their desirable elastomeric properties. The practical utilization of
these materials has been hindered somewhat by the economic
considerations involved in producing them and also the cost of the
nonconjugated diene as the third monomer. In order to circumvent the
latter problem, limonene and related monoterpenes obtained from citrus
oils were chosen as suitable third monomers. Limonene and a- and
b-pinenes have been previously homopolymerized by a number of
catalysts. Obviously in the case of EPT rubbers, the Ziegler-Natta
catalysts were the catalysts of choice.
Modena, Bates, and Marvel
found that when optically active d-limonene was homopolymerized, the
resulting polymer was optically inactive. Their work indicated that
limonene polymerized into a bicyclic structure (I) as well as the
desired structure II. The bicyclic structure was favored over the
monocyclic structure by a factor of 1.5-2. In the case of a B-pinene,
the expected structure (III) was obtained.
Results and Discussion
An experimental program was
undertaken to evaluate a series of EPT elastomers from a variety of
Ziegler-Natta type catalysts. The terpene monomers were introduced into
the reaction vessel, containing catalyst and solvent, by vapor
entrainment in the ethylene-proplene gas stream. This method was found
superior to injecting the terpene into the reaction vessel by means of
a hypodermic syringe.
The resulting polymers were
purified in the usual manner and freeze dried from a benzene solution.
The purified product was analyzed for unsaturation by the method of
Kolthoff, Lee, and Maris and for methyl group content by infrared
analysis. The intrinsic viscosity (0.4% solution in benzene) and gel
content were also determined prior to vulcanization. (Gel content was
determined by cyclohexane extraction at 23ºC. over a 24-hr.period.)
The polymers sent for
vulcanization are reported in Table I. All experimental conditions were
kept constant except the types of catalysts employed and the ratio of
aluminum alkyl to coordination compound.
The results of vulcanization
tests gave highly undercured vulcanizates. The poor results were
attributed to high gel-content and acidic residues in the polymers.
Samples I-49, I-58, I-66, I-69 and I-71 were examined by the testing
laboratory for gel content, ash content, and spectrographic analysis on
the ash residues. The results of these tests are reported in Table II.
All attempts to obtain satisfactory vulcanizates on samples I-62, I-72,
I-73, I-74, and I-79 were also unsuccessful. Analogous results were
obtained with the b-pinene terpolymers, samples II-23, II-24, II-25 and
II-28. In all cases, du Pont's Nordel EPT rubber was run as a control.
The recipes employed in the vulcanization studies are reported in Table
III.
Typical polymerization
experiments performed in this study are reported in the experimental
section. Where an insufficient amount of polymer was obtained for
vulcanization studies, it is so noted. The following catalyst systems
were examined: triethylaluminum with vanadium oxytrichloride, titanium
tetrachloride, and titanium tetraiodide; triisobutylaluminum with
vanadium oxytrichloride, and titanium tetrachloride and
diisobutylaluminum chloride with vanadium oxytrichloride and vanadium
triacetylacetonate.
It is difficult to explain why structures II and III (from
limonene and b-pinene, respectively), which are those, incorporated in
the terpolymers do not lend themselves readily to vulcanization, even
though adequate unsaturation is indicated by titration with perbenzoic
acid.
Experimental
Materials
Samples of chemical dipentene
and d-limonene were furnished by Newport Industries Division of
Heyden-Newport Chemical Corporation. The b-pinene was furnished by the
Glidden Company. Unless otherwise noted, the monomers were used without
further purificaiton. Ethylene and propylene were Matheson C.P. grade
and were used directly after passing through two towers of magnesium
perchlorate. Heptane, Phillips 99 mole-%, was purified by extraction
with sulfuric acid, dried over sodium sulfate, distilled from sodium
hydride, and stored over sodium ribbons-Triethylaluminum,
triisobutylaluminum, and diisobutylaluminum chloride (Texas Alkyls);
vanadium oxytrichloride and vanadium triacetyl acetonate (Alfa
Inorganics, Inc.), titanium tetrachloride (Matheson, Coleman and Bell)
were all used without further purification. Inherent viscosities were
determined as a 0.4% benaene solution in a No. 50 Cannon-Fenske
viscometer at 31º C.
Preparation of EPT Rubber
General procedure. A 1-liter
reaction flask equipped with efficient stirrer, condenser, and inlet
tube was flame-dried under a vigorous stream of prepurified nitrogen.
Apiezon grease N was used throughout the system. The solvent was
introduced and saturated with an ethylene-propylene gas mixture. The
source of third monomer was then connected into the system and the
appropriate amounts of catalyst (dissolved in solvent) were introduced
into the reaction flask by means of hypodermic syringes.
Immediately, the appropriate
rates of flow of ethylene and propylene gases were begun and the
reaction allowed to run, with vigorous stirring, for the noted period
of time and at the stated temperature.
Upon completion of the
reaction, 10% hydrochloric acid in methanol (200 ml.), containing a
small amount of 2,6-di-tert-butyl-p-cresol (du Pont Antioxidant No.
29), was introduced, under a nitrogen atmosphere, to destroy the
catalyst, and the resulting mixture was thoroughly mixed with excess
methanol in a high speed Waring-Blendor. The resulting polymer was
collected on a filter and purified by repeated precipitation in
methanol from benzene. After five precipitations, the resulting polymer
was lyophilized from a benzene solution (approximately 10% in polymer)
containing about 0.1% du Pont Antioxidant No. 29. The various physical
properties were determined on the dried polymer.
Reaction
parameters. Reaction parameters are listed in Table IV.
Analysis of Unsaturation
Preparation and
standardization of sodium thiosulfate-solution. In a dark bottle was
placed 13.22 g. (0.09 equiv.) of reagent grade sodium thiosulfate and
900 ml. of freshly boiled distilled water. The resulting solution was
allowed to stand at least 24 hr. prior to standardization. The sodium
thiosulfate was standardized by titration of the iodine liberated from
a solution containing an accurately weighed amount of potassium iodate
(0.1-0.15g., reagent grade, previously dried at ~ 110ºC. for 24 hr. and
stored in a desiccator), 1 g. of potassium iodide, and 50 ml. of 0.4M
acetic acid solution to a starch endpoint.
Base-catalysed isomerisations of
terpenes
The panorama of
base-catalysed isomerisations of terpenes is an important part of aroma
chemistry. Major contributions in this area are presented here under
sections on hydrocarbons, alcohols, aldehydes, ketones, acids, esters,
and epoxides.
Hydrocarbons
p-Menthenes. Pines and
Eschinazi introduced sodium-organosodium catalysts, for example sodium
'benzylsodium' catalyst (prepared by treating an excess of sodium in
toluene with o-chlorotoluene) for isomerising the title compounds. One
of their main findings is that when (+)-p-menth-1-ene (1),
trans-p-menth-2-ene (2) or p-menth-3-ene (3) is refluxed at 168-175º
for 20-22 hrs with the catalyst, the isomerisate is an equilibrium
mixture of (3) (63%), (1) (32%), and p-menth-8 (9)-ene (4) (5%). The
rate of racemisation of (+)-(1) is relatively faster than that of its
rate of isomerisation and (+)-trans-(2) reorganised to (+)-(1). There
is no formation of p-cymene (5). The mechanism proposed involves
intermediate carbanions.
More recently, Ferro and
Naves studied the isomerisation of (1), (3), (4) (cis and trans) and
p-menth-4(8)-ene (6) with sodium-organosodium catalyst (catalyst S,
prepared according to Pines and Eschinazi, xylene replacing toluene)
and analysed (by GC) the products formed at reflux temperatures. Under
these experimental conditions, there is no equilibrium of the
p-menthenes. Thus, (3) is obtained from (+)-(1) and cis-(4) in 52.1 and
78.6% in 48 and 6 hrs respectively; trans-(4) however, is less reactive
than its stereoisomer.
Further, the behaviour of the
p-menthenes toward n-lithioethylenediamine (catalyst L) at 50º and
potassium tert-butoxide (t-BuOK) in dimethylsulfoxide (DMSO) (catalyst
B) at 100º was evaluated. By a 4 hr treatment with catalyst L, (+)-(1)
only a small amount of the racemate resulted and with catalyst B, the
racemisation rate increases of 16% in 2 hrs without isomerisation.
Reaction of cis-(4) and trans-(4) with catalyst L furnishes (6) in 76.9
and 48.6% (in 4 hrs) and with catalyst B, 77.0% (in 8 hrs) and 64.3%
(beyond 12 hrs) respectively. Use of catalyst S is recommended for the
preparation of (3) from (1) and of catalysts L and S to obtain (6) from
(4) (cis and trans).
Kinetically controlled
regrouping of p-menthenes with calcium amide catalyst in the liquid
phase gives equivalent mixtures of isomers with exo and endocyclic
double bonds.
o-Menthenes. Rearrangements
similar to p-menthenes are observed in the interaction of the sister
o-isomers with calcium amide catalyst.
p-Menthadienes.
Investigations on base-catalysed rearrangements of this family of
hydrocarbons were reported by Pines and Eschinazi. On reluxing
(+)-limonene (7) with sodium 'benzylsodium' or sodium hydride catalyst,
rapid racemisation occurs with evolution of hydrogen, providing
p-cymene (5). Interruption of the reaction when the optical rotation
drops to ~20% gives a catalysate that includes 20% of (+)-(7), 50% of
(+)-(7) and 20% of a mixture consisting of p-mentha-2,4(8)- and
p-mentha-3,8(9)-diene (8) and (9) in the approximate ratio 4:1 and 1%
of (5). Without a promoter but in the presence of sodium at relux
temperature, (+)-(7) only undergoes racemisation without aromatisation.
With the catalyst, the intermediates (8) and (9) are reversibly
isomerised; on the other hand, (—)-a-phellandrene (10) loses optical
activity and gets dehydrogenated to (5) with no signs of condition to
(8) and (9). Invoking carbanions these changes have been explained.
Swiss investigators have also
tracked—in the same way as p-menthenes—the transformations of
p-menthadienes. When reacted for 1 hr with catalyst L at 50º, (+)-(7)
gives an equilibrium mixture of (8), (9), g-terpinene (13) and
a-terpinene (14) in the proportion 14:50:30:3 with increasing
conversion to (5), depending on the reaction time. On processing with
catalyst B, the substrate is practically effected in 5 hrs at 100º and
equilibrium is realised. Under refluxing conditions, catalyst S
generates (8) and (9) in the proportion 11:1.
Terpinolene (11), isolimonene
(p-mentha-2,8(9)-diene) (12) and g-terpinene (13), with the exception
made for the latter in the case of catalyst S, respond in a similar
manner. With catalyst L, the equilibrium of (11), (12) and (13) is
attained in 30 min and with catalyst B, in 15 min. Complete
isomerisaton is achieved in 6 hrs with catalyst S, leading to (8) and
(9) in the approximate proportion 11:1 As against these, with catalyst
S, (13) changes completely to p-cymene (5) in 15 hrs.
The study with the conjugated
dienes (8), (9), (14), and p-mentha-2,4-diene 15) has led to
interesting results. Equilibrium between (8), (9), and (14) is attained
by the action of catalysts L and B. Divergent behaviour is displayed
with catalyst S; the cyclic dienes (14) and (15) only give (5) (100 and
90% in 24 hrs); (8) equilibrates with (9) in the approximate ratio
11:1. A modified carbanion mechanism has been advanced to explain this
reaction.
Using pines and Eschinazi
catalyst, isoterpinolene (8) has been synthesised from (+)-limonene (7).
A kinetic study of the action
of t-BuOK-DMSO system on (±)-limonene indicates that the initial
products of isomerisation is a 5:3:1 mixture of (8), (13), and (14) and
that the pseudo-first-order rate constant of 55º is 4.5 x 10-6 sec-1.
Under the experimental conditions, (8) and (14) afford the same
products in 30 min. Hence the slow step in the isomerisation is the
migration of the double bond to the exoposition.
From the above synthetic mixture
derived from (±)-limonene, by precise fractionation, (8) is recoverable
in 11% yield. Since the sister isomers can also bereverted to this
mixture and recycled, this is an elegant method for the large-scale
preparation of this unusual hydrocarbon.
Whereas (±)-p-mentha-2,
4(8)diene (8) is convertible to (±)-menthol isomers, it is the (±)-8
that is higher priced, being a possible precursor in the synthesis of
(—)-menthol. Technically, a facile route to this hydrocarbon is from
(±)-isolimonene (12) by contact with t-BuOk-DMSO combination at room
temperature.
In the rearrangement of
p-menthadienes catalysed by t-BuOK-DMSO at 55º, only three constituents
of the isomerisate have been identified. A fuller picture of the
equilibrium composition, conditions for achieving it with 76.2%) with lesser amounts of
m-mentha-1-8diene (19), m-mentha-6,3(8)-diene (20)
m-mentha-1(7),8-diene (21), and m-cymene (22); at 100º aromatisation is
complete. By reaction with t-BuOK-DMSO system at 82±2º for 3 hrs,
sylvestrene (17) affords (18) (45.0%), (19) (3.0%), (20) (5.5%), and
(21) (0.9%) 13. With the same catalyst, the hydrocarbon (18) largely
resists rearrangement but the sister isomer (20) smoothly conjugates to
(18).
(+)-Car-3-ene. Ohloff and
coworkers accomplished the base-catalysed conversion of (+)-car-3-ene
(23) to (+)-car-2-ene (24). The reaction of (23) with
N-lithioethylenediamine for 1 hr at 100º results in an equilibrium
mixture of the 3- and 2-isomers in the ratio 3:2, accompanied by
cymenes equivalent to 2%. From the catalysate, enriched (+)-car-2-ene
(80%) is obtained by fractionation. Others have followed this trail.
Theroretical reasons have been advanced to account for the greater
stability of the 3- over the 2-isomer. From the equilibrium constant
1.50, the free energy difference is extracted as 240 cal/mol at 25º.
A disadvantage of the above
technique is the concurrent release of the cymenes. However, under
regulated conditions, use of t-BuOK-DMSO catalyst eliminates this
defect and the reaction generates a clean equlibrium mixture consisting
of 40% (+)-car-2-ene and 60% (+)-car-3-ene.
While today more advanced and
different syntheses for (—) menthol are used, patents granted to Booth
combined with that to Webb are classies of the technical exploitation
of (+)-car-3-ene for a (—)-menthol synthesis. The outstanding step in
the chain of reactions is the rearrangement of the terpene to the
2-isomer. In general, basic catalysts recommended consist of strong
bases, applied under conditions when carbanions of a hydrocarbon can be
formed and these include simple or complex alkali metal alkyls, also
strong bases such as alkali metal alkoxides, and alkali metal amides,
which are advantageously used in media that encourage the maturing of
their basicity. Examples of the catalysts are activated sodium of the
Pines type, sodium and/or potassium derivative of y-picoline, t-BuOK in
DMSO, N-lithioethylenediamine, and Na or K metal on Al2O3.
Here we may digress a little.
Above 180º, in the presence of the basic catalyst, (+)-car-2-ene (24)
decyclises to (+)-isolimonene (12) and the latter conjugates to
(+)-p-mentha-2, 4(8)-diene (8), the pivotal hydrocarbon in a (—)
menthol synthesis. The next stage is the migration of the exo double
bond of (8) to give an equilibrium mixture of a-terpinene (14) (50%),
g-terpinene (13) (20%), isoterpinolene (8) (25%) and p-mentha-3,
8-diene (9) (5%). Finally the p-menthadienes get dehydrogenated to
p-cymene (5). For these reasons, the correct temperature and time must
be chosen to terminate the reaction at the isoterpinolene stage.
Catalysts which rearrange (+)-car-3-ene to (+)-car-2-ene will also
perform this function.
Ferro found that Ohloff's
reaction when conducted at 110º for 5 hrs gives an equilibrium mixture
of (+)-car-3-ene (23) and (+)-car-2-ene (24) (55:45) with cymenes
(12%); an 18 hr run augments aromatisation (20.4%). Also, the findings
of Acharya and Brown using t-BuOK-DMSO have been fully substantiated.
There are valuable data on
the isomerisation of (+)-car-3-ene (23) over basic catalysts such as
MgO, Cao, SrO2, Y2O3. La2O3 and ZrO2 by the pulse method. The reaction
has been tracked in detail over MgO (I) and MgO (II) and CaO (II)
catalysts. Rearrangement of (23) to (24) is the dominant change, by
synchronised two-way decylisation leads to a-terpinene (14) and
m-mentha-1,5-diene (25) and further dehydrogenation to p-cymene (5) and
m-cymene (22). From a tracer study with deuterium it is inferred that
the double bond shift is most likely to proceed via II-allylic anion
(26).
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