466 THE CHEMISTEY OF ESSENTIAL OILS
OIL OF OPOPANAX.The oil from the true opopanax has not been investigated, and the
botanical source of the gum-resin is unknown. It is almost certainly
derived from an Umbelliferous plant—but not Opopanax chironium as
usually stated. The commercial product known as oil of opopanax is
derived from the exudation of Commiphora erythrcea, var. glabrescens,
which is possibly identical with bisabol myrrh. Samples of the oil have
the following characters :—
Specjfic gravity 0-870 to 0'905
Optical rotation ... .... 1-4890 „ 1-4940
Acid value ......... 0 ,, 3
Ester „ 7 „ 20
,, „ (after acetylation) 4 0 , ,. 40 „ 55
The oil is soluble to an almost clear solution in 1 to 10 volumes of 90 per
cent, alcohol.
The only constituents so far identified are the sesquiterpene bisabolene,
and a sesquiterpene alcohol boiling at 135° to 137° at 2 mm. pressure.
OIL OF FRANKINCENSE.This oil is distilled from the resinous exudation of various species of
Boswellia, principally Boswellia Carterii. The yield of essential oil varies
from 5 to 10 per cent.
It is a colourless or pale yellow liquid of balsamic odour, having the
following characters:—
Specific gravity0*875
Optical rotation .•...
Refractive index .1-47
Acid value ......
Ester „ 5
,, „ (after acetylation)0*875 to 0-894. + 15°
. 1-4725
0
5
40
, +30°
, 1-4825
, 4
, 20
, 50
It is soluble in 4 to 8 volumes of 90 per cent, alcohol, sometimes with
-turbidity.
Up till about ten years ago, this oil was found to be laevo-rotatory,
but apparently the species of Boswellia from which it is obtained have
recently been varied, as the oil is almost always dextro-rotatory now.
'The laevo-rotatory oil contains a-pinene-dipentene, phellandrene, and
<cadinene.
The dextro-rotatory oil has recently been examined by Schimmel &
Co.
1
The oil examined by them had the following constants: d 150 0-8775,
«D + 19° 18', ^D2O° 1'47245, acid value 1*8, ester value 7*5, ester value after
acetylation 106*0, soluble in up to 2 volumes of 90 per cent, alcohol, the solu-
tion being clear at first, and turning turbid after two volumes. Of the ter-
penes, 92 per cent, boiled between 156° and 161°, about 5 per cent, between
161° and 163°, and about 4 per cent, between 163° and 181°. In the
fractions boiling between 156° and 157° (d 15 o 0*862 to 0*863 ; aD + 30° 58')
they established the presence of i- and d-a-pinene from the nitrosochloride
and the nitrol piperidide (melting-point 118°), as well as by oxidation into
pinonic acid (boiling-point 170° to 175° at 7 mm.; melting-point of the
active acid 69° to 70°; of the inactive acid 104°). The presence of cam-
phene in all the fractions boiling betwreen 158° and 164° was established
fey conversion into i'soborneol, melting-point 210° to 211°. Dipentene(^1) Report, April, 1914, 62.