Chemistry of Essential Oils

496 THE CHEMISTKY OF ESSENTIAL OILS

Dimethyl sulphide, CH 3. S. CH 3. The first drops of the initial
fraction (boiling-point 40° to 119°) contained small proportions of a,
highly volatile sulphur compound of a disagreeable sweetish odour, which
is probably dimethyl sulphide, from the fact that it ga,ve precipitates with
solutions of mercuric chloride and of platinum chloride, as well as because
of its very low boiling-point.
Allyl cyanide, CH 3. CH : CH. ON. The analytical values of a frac-
tion amounting to a few grams, which passed over between 120° and 123°,
and which also contained sulphur (d15o 0-8570; saponification number
47*7) pointed to the probable presence of allyl cyanide.
This suspicion was confirmed by the formation of an acid boiling at
about 184°, with an odour recalling that of fatty acids. This acid was
generated during the process of saponification with alcoholic potash. It
was oily, and when left to stand in the cold for several days it solidified
in crystals; melting-point 70°. Unfortunately, the quantity available was
too small for repeated purification and for the positive identification of
the substance as crotonic acid, of which the melting-point is 72°.
Allyl iso-thiocyanate, CH 2 : CH. CH 2. NCS, was found to form the
principal portion of the fraction, boiling between 150° and 163°. The
proportion present did not exceed 40 per cent.
About 50 per cent, of the oil was found to consist of a crotonyl iso-
thiocyanate, C 4 H 7 NCS. This substance has the following characters :—

Boiling-point

Specific gravity.

Optical rotation.

Refractive index.

175° - 176°

0-9941

+ 0°3'

1-52398

The thio-urea prepared from this substance melts at 69° to 70°and

has the formula C 4 H 7. NH. CS. NH 2.

Grimme 1 records the following percentages of essential oil in the

mustard and allied seeds set out below :—

Brassica oleracea acephala vulgaris

,, quercifolia

, ,, crispa

, gemmifera

sabanda.

capitala alba

„ rubra

gongylides

botrytis.

, asparagoides

Rapa oleifera annua

,, hiemalis

rapifera.

teltoviensis

Napus oleifera annua.

,, hiemalis

„ flora alba

rapifera (" Erdkohrabi

„ ("Wruke')

Baphanus sativus albus

niaer

Badiola

oleiferus

0-079

0-051

0-103

0-144

0-129

0-258

0-259

0-142

0-104

0-119

0-085

0-093

0-166

0-132

0-097

0-071

0-056

0-062

0-012

0-164

0-108

0-106

0-133

Numerous methods for the determination of " mustard oil," that is, of

the thiocyanate compound, in the essential oil, or in preparations thereof,.

(^1) Pharm. Zentral., 53 (1912), 733.