480 THE CHEMISTRY OF ESSENTIAL OILS
to inexplicable changes under such treatment. The decomposition effect
of a slightly too high boiling-point is made clear in the comparison 14, 14A,
these figures being from the same sample.
" On the contrary, the temperatures at which portions of sample 3 and
many further samples of Maranham and other types were distilled rose
still higher without any such changes (owing to accidental increase of
pressure). Sample 4, also a Bahia variety (as 3), was moreover further
anomalous since the rotation of the first 10 per cent, came within Cocking's
abbreviated criterion of purity, whereas on complete distillation to obtain
the difference value, this became positive owing to the marked drop in
rotation of the highest fraction, an unpublished feature for any standard
genuine oil—certainly with the correct mean rotation—confirming the
absence of decomposition changes."
In examining this essential oil, it appears certain that the optical
rotation should always be laevo-rotatory, and very rarely below - "4° or
— 5°.
African copaiba oil is always dextro-rotatory, and gurjun balsam oil is
always very highly laevo-rotatory, usually about — 80° or more. Gurjun
oil may be detected with certainty by adding five or six drops of the oil
to 10 c.c. of glacial acetic acid containing five drops of nitric acid. In
the presence of gurjun oil a purple violet colour is developed within a
minute or so. Fatty oils are indicated by a high ester value, the adult-
erant being recognisable by separation of the products of saponification.
The oil consists principally of sesquiterpenes. The early investiga-
tions are quite unreliable, the first authentic investigation being that of
Wallach,
1
who stated that the principal constituent of the oil was the
sesquiterpene caryophyllene. Deussen
2
and his colleagues have, since
then, assisted in the elucidation of the chemistry of this oil, and found
that the sesquiterpenes present consisted principally of the inactive
a-caryophyllene, but Z-cadinene and a little /2-caryophyllene are ' also
present. Deussen
3
has described a sensitive test for caryophyllene.
When /3-caryophyllene nitrosite is heated with petroleum ether there
results, in addition to dehydrocaryophyllene nitrosate, a body which is
distinguished by its insolubility and which can be purified by dissolving
it in acetone and precipitating with light petroleum. It crystallises in
the pure state in white needles, melting-point 159°. The same body is
generated when nitrous acid gas is passed into an ethereal solution of
caryophyllene. A blue coloration quickly results, and when the gas is
continued for some time a voluminous yellowish-white body is precipitated,
while the blue colour disappears. Careful recrystallisation from acetone
yields white, silky needles, melting at 160°. This body is optically active :
[OLD] - 133° 50'. Combustion established the formula C 12 H 19 N 3 Og.
Owing to its insolubility in most organic solvents, this compound is
excellently adapted for the detection and determination of /3-caryophyllene.
For this purpose from 2 to 3 grams of the oil under examination are treated
in a 10 per cent, ethereal solution with nitric oxides, the reaction-mixture
(which should be protected from light) not being cooled, and the passage
of the gas being stopped as soon as the separation of the body in question
ceases. The precipitate is washed with ether and weighed. Deussen
claims that by this method Para copaiba oil shows the presence of 5'15
(^1) Annalen, 271 (1892), 294. (^2) Chem. Zeit., 34 (1910), 873; 36 (1912), 561..
*Annalen, 388 (1912), 136.