500 THE CHEMISTEY OF ESSENTIAL OILS
Acrimyl iso-thiocyanate, or " white mustard oil," is a yellowish oily
liquid of pungent odour and unpleasant hot taste. It is prepared synthe-
tically by treating |)-hydroxy-benzylamine with carbon disulphide, and
the resulting compound with mercuric chloride.OIL OF SPOONWORT.Cochlearia or spoonwort oil is distilled from the fresh-flowering plant
Cochlearia officinalis (scurvy grass) which yields a very small quantity of
the essential oil. The specific gravity of the oil is about 0*940 to 0*960, and
it is dextro-rotatory to the extent of + 70° or thereabouts. Its refrac-
tive index is about 1'4900. Hofmann showed many years ago that the
principal constituent was secondary butyl-iso-thiocyanate, of the formula,cs. NCH(.
\CH 3
Gadamerl has shown that if the dried plant without flowers is cut
up, and some white mustard flower is added, the yield of oil is much in-
creased. From 28 kilos of the dried plant, which is known as scurvy
grass, 66 grams of essential oil were obtained. The oil boiled at 150° to
162°, and the bulk of the oil was found to be secondary butyl-iso-thiocy-
anate. A little benzyl-iso-thiocyanate is also present. The amount of
iso-thiocyanate was estimated by dissolving a weighed quantity of the oil
in alcohol, adding excess of deci-normal solution of silver nitrate, allow-
ing the whole to remain for twenty-four hours in a well-stoppered bottle,
filtering from the precipitated silver sulphide, and titrating the excess of
silver with ammonium thiocyanate solution. The fractions of the oil of
higher boiling-point (156° to 162°) had a lower specific gravity and higher
optical rotation than the earlier fractions. They possibly contained a
little limonene.
In order to determine the purity of the oil a quantity may be heated
on the water-bath with 10 per cent, of its weight of ammonia for a few
hours under a condenser, and the liquid evaporated to dryness. The
mass is then extracted with alcohol and the liquid filtered and evaporated
on a watch glass; the resulting crystals of crude secondary butyl-thio-
urea melt at 125° to 135°. Pure secondary butyl-thiourea melts at 136° to
137°. An artificial cochlearia oil exists, but appears to consist of iso-butyl
iso-thiocyanate. The crystalline thiocarbimide yielded by this melts at
93 *5°. The usual adulterants can be thus detected, as the thiocar-bimides
(thioureas) formed from them melt at the following temperatures :—
Allyl (mustard oil) 72° to 74°
Normal buiyl 79°
Iso-butyl 93-5°
Tertiary butyl 165°
OIL OF WALLFLOWEB.
The flowers of the wallflower, Cheiranthus Cheiri, yield about 0
- 06
per cent, of essential oil by extraction with a volatile solvent and dis-
tilling the extract with steam. This oil has been examined by Kumnest.^2
It is of a yellow colour, and in alcoholic solution has a blue fluorescence,
and has the following characters :—
(^1) Arch. Pharnt. (1899), 237. (^2) Qhem. Zeit. (1911), 667.