Chemistry of Essential Oils

(Tuis.) #1
0*850 to


  • 2° ,
    1-4850 ,
    1 ..
    15 ,
    68 ,


0-893
+ 2 °
1-4920
10
40'
80

116 THE CHEMISTEY OF ESSENTIAL OILS


Specific gravity at 27° 0-856
Optical rotation + 5° 40'
Acid value 1*2
Saponification value ........ 8'4
„ ,, (after acetylation) 48-7

CANNABINACE^E.

OIL OF HOPS.

Oil of hops is distilled from the flowers of the ordinary hop, Hitmu-
lus lupulus, which yield from '3 to 1 per cent. The oil glands are situ-
ated under the scales of the flowers (catkins); these grains or glands
can be separated from the flowers, and are known in commerce as
lupulin. The quality of the oil is, of course, dependent on the state of
the flowers, and when the crops have had to be " sulphured," the oil
obtained from the flowers is less valuable and contains traces of sul-
phur. The pure oil has a pale yellow to faint green tint, but can be
obtained colourless by rectification. It has a penetrating hop odour.
Its characters are as follows :—
Specific gravity ..0*850
Optical rotation-2°
Refractive index1-4850
Acid value ........
Ester „
,, „ (after acetylation) ....
It is not soluble in 90 per cent, alcohol as a rule, and often not in
95 per cent, alcohol. In 1822 Payen and Chevalier stated that there
were at least two bodies present. Wagner in 1853 obtained a terpene
boiling at 175° and an oxygenated body which yielded valeric acid on
oxidation. Personne claimed to have obtained a dextro-rotatory terpene
of specific gravity '888. The most modern and reliable investigation,
however, is due to Chapman.^1 Four samples of authentic origin gave
the following figures :—
Specific Gravity at 15°. Rotation [«]D.
1 -8802 + 0-41'
2 -8662 + 0-58'
3 -8771 + 0-50'
4 -8743 —
All these samples were free from sulphur and neutral to litmus.
No ketones or aldehydes were detected in the oil. A prolonged series
of fractionations at 60 mm. pressure yielded the following fractions:
(1) 89° to 91°; (2) 145° to 150°; (3) 163° to 168°; (4) 168° to 173°.
The first and fourth were the main fractions, the second and third being
very small. Fraction No. 1 was a colourless oil, practically unacted
upon by sodium. When distilled from this metal, it boiled at 86° to 89°
at the same pressure. Under ordinary pressure it boiled at 166° to 171°
almost entirely, but towards the end, the temperature went up to 250°,
due to polymerisation of the original substance. The specific gravity
at 20° was found to be -799 and the rotation - 0'56'. It is clear that
this body is not a normal terpene, and Chapman's experiments lead
him to consider it as a mixture of tetrahydrocymene, and one of the so.
called "olefenic'terpenes," bodies as yet but little understood. Frac_.

\Jour. Chem. Soc., 83 (1903), 505; 67 (1895), 54 and 780.
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