Chemistry of Essential Oils

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.