-i
~
IL
-*t
DEPOSITED
BY
THE
C01'v11'v1ITTEE
<Brabuate Stubies.
M~C(JLL
UNIVEI\51TY
LIBRA~Y
ACC . N o .
~
~
DATE
ON
__j
.
A 8TUDY OF THF. CONSTITUENTS OF
B?VEA
RESIN
AND 8ERUI;·r.
1',
THE
ACID~
OF
HE'I;1'~A
RESIN
THESIS
Presented by Frederic Harrison Yorston in partial fulfillment of the requirements for the degree, Master of Science.
May,
1924-~
McGill University.
THE ACIDS OF HEVEA RESIN.
At the present time the tree Hevea Brasiliensis is the
only important source of rubber.
The raw rubber formed by
the coagulation of Hevea latex consists mainly of the hydrocarbon caoutchouc; and with the caoutchouc is associated protein
and a somewhat variable amount of acetone soluble substances called
collectively the resin.
It may be stated on general grounds
that a full knowledge of the chemical nature of rubber is
essential to its most efficient utilization.
There are consider-
able differences in the vulcanization properties of rubber
prepared by different methods and there are, as with alJ natural
products, variations in quality of similarily prepared specimens
from season to season and froM tree to tree.
These differences
have long been recognized, and it seems reasonable to suppose
that they might be due, in part at least, to variation in the
amount or nature of the
non-~aoutchouc
constituents and hence
to conclude that these substances take an active part in
vulcanization; yet the chemistry of these constituents has
only recently been the subject of exhaustive study.
1....t..
Whitby and Dolid
examined the resin of a number of
large samples of crepe and sheet rubber.
On concentration
of the acetone extracts solids crystallized out and, by methods
which will be described briefly in the experimental part of
this thesis, were separated into the following constituents:
1.
J. Dolid
Thesis, McGill University, 1923.
(2)
Quebrachite, methyl laevo inositol
(0.005 - 0.01)
d-Valine, dextro aminovaleric acid
( .005)
A Sterol
( .02 - .05)
Esters of a sterol
( .05 - .1)
A phytosterOlin, a sterol glucoiide
( .05 - .1)
A new acid
c20H42 o2 ,
named heveic acid ( .15)
The numbers in parentheses are of the order of the
percentages of the constituents in rubber.
The mother liquor from which these compounds separated
was found to contain a mixture of liquid unsaturated acids
usually amounting to about
85% of the resin.
From consider-
ation of the acid number and iodine value it was thought
probable that the principal constituents were oleic and
linoleic acids together with substances af a resinous nature.
The identification of these
object of the present work.
li~1id
aoids is the main
A secondary aim is the accumul•
ation of the above-mentioned constituents for an investigation
of their properties.
Vfuitby and Dolid obtained no water-soluhle acid other
than d-valine and no steam-volatile acid:
hi~her
fatty acids
and possibly resin acids seeffi to be the only acids in Hevea
resin.
The separation of the constituents of a mixture of
fatty acids ia ·essential if their identity is to be established
definitely; but such a separation is hard to carry out even
when a large amount of material is available. Most of the
methods employed depend upon differences in the solub±lities of
various soaps.
As the higher acids in an homologous series differ
only slightly in composition and properties many fractional
crystallizations are required to yield the chemical individuals
in pure condition.
Such methods are not satisfactory even when
applied to the simpler case of the separation of the solid
saturated from the liquid unsaturated acids. 2 ) Probably the best
general method of separation is the fractional distillation of the
f
methyl estersat low pressure; but a considerable quantity of
"'1
material is needed and in the case of the ~saturated acids
,
repeated distillation causes great loss by polzerization.
Tes~s
for the commonly occurring eighteen carbon atom unsaturated acids
are often made by bromination and by oxidation with alkaline
permanganate; this process yeilds
crystalline derivatives of
..
........--~
oleic and linoleic acids, that of linoleic and linolenic acids.
These tests will be discussed at some length as the conclusions
to be drawn from this investigation are mainly based on them.
OXIDATION: Careful oxidation of an ethylenic compound
results in the
ad.~ition
of two hydroxyl groups at the double
bond , thus:
=
2.
H
R
R
H
c'
' c
/
...,OH
OH H
I
c ...._R
A quantitative separation of oleic from stearic acid
through the thallium salts has recently been claimed
C.A. 17
643
(1923)
7
(4)
Furthur oxidation of the glycol brings about scission with the
formation of carboxy acids:
R
OH
'd
H"
-
OH
c/
........
H
R COOH + R COOH
R
Identification of the compounds obtained in the second
step of this oxidation has served to establish the nositions
of the double bonds in oleic and linoleic acids, but for the
detection of these acids it is the hydroxy derivatives which
are desired.
Unfo~tunately
the further oxidation of part of
the hydroxy compounds cannot be prevented.
The dihydroxy acid derived from oleic acid cab be attained
in good yeild but apparently not in a very pure form, for
although it is usually stated to melt at
as low as 125° are recorded.
137° melting points
A specimen prepared by the writer
from Kahlbaum's oleic acid melted at 12S0 after several
recrystallizations.
As this dihydroxy stearic acid has two
asymmetric carbon atoms it can exist in four optically active
modifications or as two dl-mixtures.
Ome mixture is that
derived from oleic acid, the other, melting at 996, from the
stereoisomeric elaidic acid.
As would be expected, two dl-mixtures of tetra hydroxy-·
stearic acids, called sativic acids, are formed in the oxidation
of linoleic acid.3)
3.
It was once thought that ordinary linoleic acid was a
mixture of two stereo isomers; (Lewkowi tch,""EJ. Voii,ip·,07)
_.
Nico1et and Cox (J. Amer 44, 144, 1922) eonsider the
of twm sativic acids by oxidation, evidence
for this view.
~roduction
The two mixtures differ slightly in solubility; Nicolet
and Cox4) found that the two dl-components could be obtained
pure only after w.any fractional crystal} izations.
melts at 153°, the other at 171o.
One of them
Accordinglv the product first
obtained does not melt sharply and identification of linoleic
acid cannot be made on the basis of this
melti~g
point.
Fractionation of the mixture into constituents having the above
~
/
-~elting
points would cake the identification of ordinary linoleic
acid practically certain, while the analysis and location of the
hydroxyl groups by further oxidation would not distinguish between
this acid and one of the three eteroisorners theoretically capable of
existence.
similar to
It is true that no acid (except elaeostearic acid)
~inoleic
acid has ever been definitely identified,
but linoleic acid occurs mainly in fats and is not mentioned
in Beilstein to
occu~
free.
If other such acids can be
elaborated in nature they might conceivatly occur in a product
like latex the mechanism of production of which is presumahly
quite
dif~erent
:rom
th~t
of a fat.
But examination of a
mixture of sativic acids would require a moderate quantity of
--
substance and only small yeilds can be obtained by oxidation.
Rollet got
40.7%
from pure linoleic acid, and the writer in
one experiment was not so successful.
As the formation of
the hydroxy derivatives is essentially the addition of the
elements of hydrogen peroxide at each ethelenic linkage it
was thought
possible that larger Lei.lds might be obtained
by treating the unsatured acid with hydrogen peroxide.
4.
Lee. Cit.
(6)
In one experiment linoleic acid was treated with an
eth~l
solution of pure hydrogen peroxide5)but no sativic acid could be
isolated from the reaction mixture.
Linolenic acid converted by permanganate oxidation to
hexahydroxystearic acids of which only small
obtained.
--
y~Jlds
can be
The process accordingly cannot he used for the
detection of linolenic acid.
BFO~~tNATION;
Oleic acid gives rise to a dibromostearic
acid which is an uncrystallizable oil; so that brorr1ination
cannot serve to identify oleic acid.
Linoleic acid 6ives about a fi:ty percent yifld of a
crystalline tetrabromide melting at about 114°.
tetrabromide is also formed.
A liquid
In this case, an account of
the marked difference in properties of the two
one of them can be purified fairly easily.
prod~cts,
A melting point
determination and an analysis of the solid oromide would
make the identification of linoleic acid fairly certain.
Linolenic acid forms a crystalline hexabromide insol,J_ble in ether and melting at 180°.
5.
The conditions were suggested by Dr. 0, Maass.
After descri1:;ing "the procedures used currently for
isolating or identifying the various fatty acids" Andre6)
draws the following conclusions:
"In many cases their
inaufficience is manifest, especially as regards the liquid
unsaturated acids.
To test only for oleic, linoleic, and
linolenic acids is begging the question by assuming a priori
that there are no others.
"When we read certain analyses published recently we very
often see that these methods, however insufficient, are not even
rigorously applied.
The fatty acids are separated into liquid
and solid acids, it is admitted implicitly that the solid acids
are a mixture of palmitic and stearic acids; the melting point
is taken, the acid number by which the mean molecular weight
can be calculated is determined, and it is concluded, without
pushing the investigation
furth~r,
that the
o~~served
character-
istics correspond to those of a mixture of palmitic and stearic
acids which would contain an amount A of the first, B of the
second.
"For the liquid acids what is called the hexabromide test
is
perfor~ed;
usually
it~,ia
this makes it possible to identify linolenic acid;
negative.
Then it is concluded that the mixture
contains only oleic and linoleic; the determination of the
iodine number makes it possible to calculate the proportions
of these constituents".
6.
Bull. Soc. Chim. 31
475,
1922.
GENERAL
METHOD~
AND RESULTS.
In the present investigation the acetone extracts
of two lots of pale crepe were examined.
The first was
kindly supplied by Dr. Bedford of the B. F. Gooderich Co.,
the second was prepared from twelve kilos of crepe from a
lot which had been examined by Whitby and Dolid.
The first extract was separated into crystalline and
1 iquid parts.
From the so:!. id were o"t· tained specimens of
quebrachite, sterol ester? phytosterolin, and a solid fatty
acid.
The solid acid was not pure heveic acid and may prove
to be a mixture of heveic and stearic acids.
The acids which
formed the bulk of the liquid part were purified somewhat by
esterification and distillation of the esters.
It was shown
by hydrogenation of a sample of the acids regenerated from the
esters that the acids are entirely derived from stearic acid7)
On account of experimental losses of liquid acids and of small
yeilds of derivatives the results of the bromination and
oxidation tests were not perfectly definite, but it is very
probable that the mixture consisted larsely of ordinary oleic
and linoleic acids.
No evidence of the presence of linolenic
or other unsaturated acid was obtained.
7.
The ·experiment was suggested by Dr. Y!hi tby ;- it has
not, to the writers' knowledgeJbeen used for the
identification of acids.
By assuniing
that the amount of saturated acid in the mixture
was negligible and that the impurities were neither acidie nor
unsaturated it may be shown from the iodine value (140).and the
acid number (corresponding to an equivalent weight of 317) that
about twice as much linoleic as oleic was present.
In the examination of the second lot of resin an attempt
was made to obtain a mixture of all the acid so that the
proportions of the constituents in the rubber could be estimated.
To this end the acetone extract was evaporated and
with aqueous potash.
sa~.onified
This vigorous treatment oaused loss of some
constituents but it saved time.
Partly because of an ill chosen
method of purification of the soaps, partly because of the
formation of a salt of the
satur~ted
acid with the metal of the
extractor, the composition of the acid mixture liberated from
the soap did not exactly represent the relative proportions
o! the acids in the rubber.
higher percentage of
case.
t~1e
An analysis indicated a somewhat
more highly unsaturated acid in this
Whitby and Do:id had found heveic acid but no stearic acid
in the lmt of rubber from ·vhich this mixture was prepared; and
therefore it was thought advis:1ble to repeat the oxidation test
fM
in order to make certain th.a t. the \i JSa tura ted acids were not
1
derived from a
c20
acid.
This time more material was available
and larger amounts of oxidation products were obtained.
Although
examination of the products is not complete at the present writing
there seems to be no reason to doubt that the unsaturated acids
in this rubber also are oleic and linoleic.
(10)
As was shown
~Y
Dr. F. B. Power of the Wellcome Research
Laboratories, and his eo-workers, many of the resins obtained
by extracting plants with organic solvents contain free acids,
but never in large amounts.
detected in a few cases.
fact that it consists
Free oleic and linoleic acids were
Hevea resin is thus remarkable for the
la~gely
of these acids. The acids form an
appreciable proportion of raw rubber:- about 1.5% of most pale er
crepes, and a larger percentage of other forcs of rubber, notably
the new "Later Sprayed"8)
8.
Whitby and
~inr.
Whitby and Allan
J.S.C.l.
~
336.
Unpublished Investigation.
A
STUDY
OF THE CONSTITUENTS OF HEVEA RESIN AND SERUM
1.
THE ACIDS OF HEVEA FESIN
EXPERIMENTAL PART
(12)
THE EXAMINATION OF EXTRACT 1.
The extract received from Dr. Bedford was a thick brown
liquid smelling faintly of acetone.
in suspension.
It contained some solid
The whole amounted to· 300 grams.
The mixture was chilled, dilute4 with cold acetone, and
the solid was separated by decantation and filtering.
The filtrate
and washings, after evaporation of the added acetone and standing
in the cold, deposited a little more crystalline substance which
was not entirely separated because the mixture was too viscous to
filter cold and on allowing it to come to room temperature much of
the solid redissolved.
THE SOLID.
The solid first obtained was brown and soft, in amount
67 grams.
It was separated into its constituents by the method
devised by Whitby and Dolid for their "Resin An, a production
which
crystallized from a relatively dilute extract on long
standing in the cold.
The solid was extracted with chloroform in a small soxhlet
apparatus.
The residue left om_ evaporation of the solvent was
brown and buttery.
It was separated by several
from alcohol and ethyl acetate into
soluble~
t~o
cryst~lizations
constituents.
The less
of which a gram was obtained, melted at 91° - 930 and
proved to be a sterol ester; the more soluble, in amount 7 grams,
was a fatty acid.
THE SOLID FATTY ACID.
The acid was pale yellow in color even after several
crystallizations and it melted over a range at about
67 - 69°.
1.357 grams required 25.65 cc. of 0.17.92 N
potassium hydroxide solution. ~bence the
equivalent weight of the acid was 295.
The molecular weight of stearic acid is 284- and it melts
at
69.2°.
at
6~
.,.,./~
Hevea acid has a molecular weight of 312 and melts
- 64-0
•
In order to
whether the substance was impure
deterr:~ine
stearic acid or a mixture of acids a further purification,
which would not sensibly change the proportions of similar
fatty acids in the material, was attempted. The acid was
dissolved in alcohol and neutralized with a
aqueous potassium hydr-oxide.
lit~le
concentrated
The soap solution was diluted with
water and treated ··ci th diinormal barium chloride solution.
The
precipitated barium salt was collected, washed, dried, and
extracted with ether.
The small residue left on evaporation
of the ether gave a strong sterol calor reaction.
The acid
was liberated from the barium salt by long boiling with
hydrochloric acid and was recrystallized from alcohol.
As the acid still retaimed some barium it was boiled five
hours with dilute hydrochloric acid and was then recrystallized
from aqueous acetone, aqueous acetic acid, and chloroform. The
68.5° - 69.5°.
0.2170 gram required 9.5 cc. 0.0780 N KOH.
acid was then nearly white and melted at
Whence,
equivalent '.veight = 293.
(14)
This would indicate a mixture of two parts of stearic
acid with one of Heveic acid.
As the amount of material
remaining is too small to permit fractionation into the
constituents, the composition will be confirmed, if possible,
by a combustion analysis.
Q.UEBRACHITE.
The solid
with water.
a~ter
extraction with chloroform was extracted
The aqueous extract deposited quebrachite after
concentration and treatment with alcohol ..
PHYTOSTEROLIN.
The remaining solid dissolved almost entirely in hot
pyridine, and on treatment with water and cooling the solution
deposited
7.4 grams of a white powder.
This melted with
decomposition at 265° and on treatGent with acetic anhydride
gave an acetate melting after
recrystallization at 162- 63°.
The acetate of the phytosterolin obtained by
~~itby
and Dolid
melted at 163°.
ASH.
A .Strut {(
.All amount of black substance remained undissolved by
I
the pyridine.
It gave on ignition 23 milligrams of ash
having roughly this composition:
si o2 ..•••••..•...•.••.. :;o%
Fe203 •................. 15
CaO ..........•.••• present
:WfgO •••••••.•••••••••••• 1 0
(15)
THE LIQ,UID RESIDUE.
The liquid residue, freed as far as possible from
crystallizable substances, was steam distilled as Whitby
and Dolid had found that the process served to remove some
nitrogenous water-soluble constituents as well as the last
traces of acetone and its condensation products.
During the
distillation the water and the oily residue formed an
·e~ulsion
so that subsequent separation of the two layers was tedious.
At this state in the earlier investigations sone resinous substances
~ad
been separated from the oily acids by
extraction of the soap solution with ether.
saponification and
A trial of the
procedure in the present case showed that separation of the soap
solution from the ether would be
al~ost
i~~ossible
on account of
the formation of a very stable emulsion; so that a different
purification of the acids was tried.
The oil, stil: mixed with some emulsion, was taken up
in ether and an aqueous layer which then separated was run
off.
future
Some
re~aining
ex~mination.
emulsion was separated and set aside for
The
ethe~al
dried and the ether was rerLoved.
solution of the acids was
The residue was mixed with
an equal volut-.e of methyl alcohol and esterified by treatment
with a stream of dry hydrochloric acid gas for two hours.
In order to prevent the addition of hydrochloric acid to the
double bonds of the acids the reaction
~ixture
was kept at 0°.
The product was poured on cracked ice and after some time an
acid aqueous layer was run off.
An oily layer was dissolved
(16)
in ether and washed with water until the washings no longer
contained mineral acid.
Here again washing was difficult
on account of the formation of an
e~ulsion,and
although the
usual dodges for breaking up such an emulsion were tried, the
washing required ten days.
The ethef'al solution of the esters was dried and the
ether was removed.
The esters were partly distilled into a
receiver connected to a Toepler pump.
This was not a very
satisfactory arrangement for as each stroke of the pump
suddenly reduced the pressure in the receiver the contents
of the distilling flask boiled violently and some colored
substance was splashed into the distillate.
A bath of paraffin
oil containing resistance wire wound on tiles formed a convenient
source of steady heat.
Between 195° at 9 mm. ~nd 185° at 5 mm.
60 grams of an oil, the separate drops of which were colorless,
distilled.
The dark viscous residue larger in aEount than the
distillate, was subsequently heated to 250° under a
pr~seure
of 2 mm. but little of it distilled.
The distillate was saponified with alcoholic potash and the
soap was decomposed by dilute ·sulphuric acid.
were collected and
dried.;~s- before~ .. .,
oil which deposited a
lit~le
at room temperature.
The mixture was
The organic acids
The acids formed a dark
crystalline material on standing
exa~ined
as follows:
A.
ACID NUMBER.
l
.
0. 6916 gram required 12.25 c. c.a. of 0.1792 N
potassium hydroxide solution.( Whence the mean
equivalent weight= 317.
·
B.
IODINE VALUE.
0.2512, 0.2048 gram required Hubl's solution
equivalent to 28.6, 23.5 c.cf, .. of a thiosulphate
solution, 1 c.c. of which was equivalent to
0.0122~ gram of iodine.
Whence the iodine value=
14-o, 14-1.
C.
OXIDATION.
3 grams of the mixed acids was neutralized in alcoholic
solution with potassium hydroxide, the alcohol removed, and the
)
I
soap dissolved in
200
c.c~.
of water.
The solution was cooled
and slowly treated with a solution of 3 grams of potassium
permanganate in 200 c.c$. of water.
The manganese dioxide which
precipitated was reduced and redissolved by sulphur dioxide.
The acids which then precipitated were collected, dried, and
extracted with cold ether.
ether was treated with
The residue on evaporation of the
ca~bon
tetrachloride.
The part soluble
in carbon tetrachloride melted after recrystallization at about
60° and was probably an impure saturated acid.
The part insoluble
in carbon tetrachloride amounted to 0.05 gram, melted at 124- 126°,
and
showe~
an equivalent weight by titration of about 320 or 330.
The dihydroxystearic acid from oleic acid melts at 128° (1370)and
its molecular
w~ight
is 316.
The oxidation product insoluble in cold ether was crystallized
from aqueous ~lcohol, 0.4-2 gram of substance melting at 160 - 175°
was obtained.
The substance was partly extracted with boiling water,
from which crystals separated on cooling.
The crystals melted at 155° -156°.
0.1682 gram required 2.63 c.cJ. of 0.179 N
alkali.
Whence the equivalent weight
= 356.
The sativic acids from linoleic acid melts at 153° and 171°
respectively, the more soluble melting at the lower temperature.
The molecular weight of sativic acid is 348.
D.
BROMINATION.
A sample of brominated in cold eth·erial solution by
Muggenthaler's method.
No ether-insoluble broMide was obtained.
On warming to remove the ether the residue became overheated and
changed in an instant to a black tar.
A second lot gave a small amount of a
bro~ide
recrystallization from petrolic ether at 112°.
bromide mel ta at 1136 - 114°.
m.elting after
Linoleic tetra-
(19)
E.
HYDROGENATION.
g. 63 grams of the 1 iquid acids was dissolved in 50 c. c/.
of ether to which was added 0.5 gram of platinum black deposited
on finely divided barium sulphate.
Hydrogen, washed with potassium
permanganate, silver nitrate, and potaSsium hydroxide solutions
and stored in a burette over strongly alkaline sodium hydrosulphite
solution, was allowed to enter the (evacuated) flask containing the
acid and catalyst .. The flask was shaken vigorouslj and hydrogen
was allowed to absorb at atmospheric pressure.
steep slope of the vapor pressure
On account of the
curve of ether at the temperature
of the laboratory (25°) the rate of absorption could not be followed
exactly.
!
After five hours 200 c.cs. had been
of absorption was then only
ta~en
17 c.cs. per hour.
up but the rate
The shaking was
interrupted for nine hours and when it was re-started no more
absorption took place.
Shaking the catalyst with air did not
revive it; so it was filtered off, dissolved in aqua regia and,
together with :resh potassium chlorplatinate equivalent to 0.5
gram of platinum, was r~pricipated as''!black by formaldehyde and
~---..........-~
..... --- -
----
-~·
-
sodium hydroxide solutions •. The fresh catalyst was ad.J.ed to the
ethe~~l
solution but unfortunately the alkaline
became sucked into the flask.
~ydroaulphite
This formed soaps and there was
some loss in recovering the free acids from the mixture,.,-1 t was
necessary to work quickly after acidification of the mixture in
order to avoid contamination with any hydrogen sulphide liberated
from the
hydrosulp~ite.
On restarting the experiment 410 c.c~.
I
of gas was absorbed in two hours and a half; the reaction then
stopped 4uddenly.
A total of
619 c.c$. of hydrogen was taken up:
(20)
~hile
the iodine value of the acids indicated a possible
absorption of 1100 c.cs.
The ether was separated from the
platimum and evaporated.
Crystals
w~ich
separated were
crystallized from ethyl acetate, when they melted at 6~.5°.
By
recrystallization froL. alcohol the melting pojnt was raised
to 69° and after another crystallization from chloroform to
69° - 69.5°.
0.3262, 0.3270 gram required 15.0, 14.8 c.cs.
of 0.0780 N potassium hydroxide. Whence the
equivalent weight of the acid= 2~1, 284.
Stearic acid selts at 69.2° and the molecular weight is 284.
A total of 3.66 grams of stearic acid was obtained, and the
final mother liquor left on evaporation a brown mass weighing
2.34 grams,so that stearic acid constituted at least 60% of the
product.:Quantitative hydrogenation should have given a product
88% saturated acid.
The stearic acid could not have been obtained in so pure
a form if any Sil:-1ilar
derived from stearic
saturated acid, or unsaturated acid not
ac11~
had been
p~esent.
(21)
EXAMINATION GF THE SECOND EXTRACT.
PREPARATION.
Pale crepe, rolled in previously extracted cloth, was
treated with acetone in a large
the soxhlet type.
a total of 11
~alvanized
iron extractor of
Each portion was extracted for a week and
kilos was used.
The acetone was distilled off
the extract and the residue was boiled with water in order to
drive off mesityl oxide formed by condensation of the
solven~
and to extrac-t quebrachite, d-valine, and any other water soluble
constituents from the resin.
The resin, a soft brown mass, was
filtered off and to it was added a little oil which had run
through the filter and some solid which had accumulated in the
extractor. The
~~:hole
amounted to 300 grams.
THE WATER EXTRACT OF THE RESIN.
The aqueous extract was a clear light yellow liquid, acid
to litmus.
An ether extract of it gave on evaporation a few
drops of a brown oil.
The aqueous part was neutralized with
barium hydroxide and a precipitate which came down was collected
and dried.
The precipitate gave a qualitative test for nitrogen.
It amounted to 1.1 grams.
(22)
SAPONIFICATION.
The resin was boiled with
5%
aqueous potassium hydroxide,
in excess of the amount required to neutralize all the acid
known to be in the rubber, until most of the material had gone
into solution. The mixture was then evaporated, distributed on
pumice, and dried on a steam bath.
In order to remove sterol
and other unsaponifiable material the dry soap was extracted
with petrolic ether in a percolation apparatus designed by
Dr. Frederic Heyl of the Upjohn Chemical Company.
THE PETROLIC ETHER EXTRACT.
The extrac-t was a dark brown 1 iquid from which some brown
6el and a light solid separated.
The solid was found to be only
slightly soluble in petrolic ether and by a careful re-extraction
it was freed from some colored substance.
It formed when dry a
pale yellow powder which rapidly became brown in the air, and
amounted to 21 grams.
The combined petrolic ether extracts were
stron~ly
alkaline
to litmus, although the reaction was often not noticed until a
test paper dipped in the liquid was washed with ethyl ether,
alcohol or water.
Water shaken with some of the extract separated
readily and acquired no s.lkaline reaction.
Water boiled with a
little of the extract became alkaline after the ether had
evaporated and a yellowish precipitate was thrown down; and after
cooling fresh petrolic ether extracted nothing from the mixture.
A portion of the extract retained its alkaline reaction even
after several days standing over phosphorus pentoxide.
Precipi tat ea were thrown down fro:·· small portions of the extract by
methyl, ethyl, and amyl alcohols, acetone, ether, and acetic acid,
but not by hydrocarbons, pyridine, and carbon tetrachloride.
An
examination of such a precipitate might lead to the identification
of some constituent of the extract.
POTASSim~r
LINOLEATE.
The powder described above dissolved readily in water to a
soapy solution.
An acid was liberated froG: the solution and was
collected and dried as before.
It was a brown oil.
0.9348 gram required 15.4 c:cs. of 0.1785 N
alkali. ~~nee, equivalent weight of the acid= 342.
An attempt was made to purify the oil by distillation in
a stream of carbon dioxide at a pressure of 2 centimetres of
mercury.
The distillate was colored.
0.700 gram required 12.25 c.cs. of alkali.
m1ence, equivalent weight
= 3°0.
Obviously no further purification was obtained.
y
0.205 gram required Hubl's solution equivalent
to 26.6 c.cs. of thiosulphate solution of which
1 c.c. was equivalent to ,0.01225 gram of iodine.
Whence the iodine value of the acid = 158.
The iodine value of linoleic acid is 181 and its molecular
weight is 2SO.
It may be noticed that the ratio of 280 to 320 is
practically equal to the ratio of 15S to 181; so that if this is
linoleic acid the resinous matter associated with it probably has
no appreciable acid number of iodine value.
(24)
The potassium soaps
fo~:ed
in the determinations of the
equivalent weights above were oxirtized in the manner previously
described.
The acids precipitated by sulphur dioxide were dried
and extracted with petrolic ether which 'remove~0.4- gram of a
buttery substance.
Extraction with ethyl ether removed a further
0.4 gram of a brown viscous oil.
The remaining acid dissolved
completely in hot aqueous alcohol and on cocling 0.15 gram of
white crystals was deposited.
The substance melted at about 160°
and on recrystallization from alcohol at about 165°.
0.1048 gram required 1.74 c.ca. of 0.179 N
alkali.
Whence equivalent weight of the acid : 338.
The remaining oily acid was brominated in petrolic ether, in
which linoleic .tetrabromide is sparingly soluLle, at below
0°.
The
petrolic ether proved to be unsaturated and on addition of the
bromine a violent reaction took place.
No crystalline product was
isolated from the reaction mixture.
A potassium soap prepared from
Kahlbau~'s
linoleic acid
was found to be slightly soluble in petrolic ether.
THE HIXED ACIDS.
After extraction with petrolic ether the pumice was boiled
with a large volume of distiJled water, whereupon most of the
adhering material dissolved.
The solution was filtered and acidified
with hydrochloric acid as before.
washed with
boili~g
The liberated acids were well
water, dissolved in ether, washed further, then
dried, and the ether removed.
The residue on removal of the ether
(25)
amounted to 58 grams.
It was thought that-purification of the
acids by distillation of the esters would cause greater loss of
the unsaturated than of the saturated acids; so that the determination
of their proportions in the rubber, already made inexact by the
unsuspected solubility of the potassium soap in petrolic ether,
would be impossible.
A.
EQUIVALENT WEIQHT.
1.702 and 0.3678 grams required respectively
64.3, 13.8 c.cs. of 0.0780 N potassium hydroxid.e.
Whence, mean equivalent weight = 340,
B.
340.
IODINE VALUF.
0.1096, 0.1564 gram required Huhl's solution
equivalent to 13.0, 18.4 c.cs. of the t~io­
sulphate previously used. ~hence, the iodine
value of the mixture = 144, 145.
C.
OXIDATION.
The potassium soaps of 19 grams of the acids were oxidized
as before.
The petrolic ether extract of the water-soluble acid
products gave 0.96 gram of a yellow butter on evaporation.
two crystallizations this melted at 45° - 60°.
After
It was probably
an impure saturated acid.
The remaining oxidized acid gave, on extraction with ether
and concentration of the extract, 0.85 gram of white crystals
melting at 128° - 130°; and 2.7 grams of a crystalline substance
similar in solubilities to sativic acid remained.
The
exami~ation
(26)
of these two products is not complete at the present writing.
There is enough of each on hand for analyses by combustion and
the second, if possible,
wil~
be separated into its constituents
by fractional crystallization.
If it be assumed that the true mean molecular weight o..c:the acids is 282 then they constituted 83% of the mixture.
this about
acid.
Of
96;19 = 5% was saturated acid and at least 5% oleic
If the rest is linoleic acid the mixture should have an
iodine number of 137 rather than the observed 144.
The large
amount of resinous impurity in this lot of acids might in part
account for the dis~epancy.
THE ZINC SALT.
A white powder remained with the pmnice after solution
of the soap.
It was thought to be phytosterolin and a little
was dissolved in hot pyridine and precipitated by the addition
of alcohol.
The precipitate gave no test for sterol, melted at
123° - 124°; and gave a residue of zinc oxide on ignition.
Zinc pallliitate and zinc heveate were found to melt
at
about 123°.
As the rubber frorr1 which it was derived contained heveic acid
this was probably the heveate.
The zinc must have been derived
from the metal of the extractor.
In conclusion the writer begs to acknowledge the very
careful
direc~tion
•
of this investigation by Dr. G. S. \t!Thi tby .