Related entries: Mustard - Oleum Sinapis Expressum, Expressed Oil of Mustard.
Volatile oil of mustard is obtained by distillation from the dried ripe seeds of black mustard, Brassica sinapiodes, Roth. (N.O. Cruciferae), after they have been deprived of fixed oil and fermented by maceration with tepid water (below 70°) for several hours, when a reaction takes place between the glucoside sinigrin (potassium myronate) and the ferment myrosin, with the production of mustard oil. It is also official in the U.S.P. Artificial mustard oil is obtained by the interaction of allyl iodide and potassium thiocyanate in alcoholic solution; allyl thiocyanate is first formed, and under the influence of heat is converted into the isothiocyanate. Volatile oil of mustard occurs as a colourless or pale yellow, strongly refractive, mobile liquid, having an intensely pungent odour and an acrid taste. Great caution should be taken in smelling the oil, and it should only be tasted when very highly diluted. In contact with the skin it causes almost immediate blistering. Specific gravity, 1.018 to 1.030 (1.013 to 1.025 at 25°). Optically inactive. Boiling-point, 147° to 156°. Exposed to light, it gradually becomes reddish-brown, and at the same time deposits a film on the inside of the bottle. The specific gravity serves to indicate absence of chloroform, carbon bisulphide, fatty oils, alcohol, and petroleum. Phenols may be detected by diluting the oil with 5 parts of alcohol and adding solution of ferric chloride, when genuine oil gives no colouration, a bluish-green colour would indicate phenols. On distilling the oil the first and last fractions should have the same specific gravity as the original oil (absence of alcohol, petroleum, chloroform, fatty oils, or more than traces of carbon bisulphide). Allyl isothiocyanate forms a solid, non-volatile compound with ammonia. On adding excess of ammonia and alcohol to volatile oil of mustard, the odour of both disappears gradually in the cold, but more quickly on heating, while crystals of thiosinamine are formed. Thiosinamine, or allyl thiourea, crystallises in rhombic prisms, melting at 740. It has a faint, leek-like odour and taste, and is readily soluble in water, alcohol, or ether.
Soluble in water (1 in 50), in 70 per cent. alcohol (1 in 10), in all proportions of alcohol, ether, amyl alcohol, benzene, or petroleum ether.
Constituents.—The oil consists almost entirely (95 to 99 per cent.) of allyl isothiocyanate, C3H5NCS (U.S.P., not less than 92 per cent.), to which the high specific gravity of the oil is due. It also contains small and variable amounts of allyl cyanide, carbon bisulphide, and probably traces of isomeric allyl thiocyanate.
Action and Uses.—Volatile oil of mustard is an extremely powerful irritant; applied to the skin, it causes very rapid vesication. The very painful nature of blisters caused by mustard is explained by the volatility, and consequent great penetrating power, of the oil. Diluted with fifty times its volume of alcohol or Cologne spirit, or as Linimentum Sinapis, the oil is employed as a counter-irritant in cases where blisters cannot readily be applied, especially to paint behind the ear in catarrh of the middle ear.
- Linimentum Sinapis, B.P.—LINIMENT OF MUSTARD.
- Volatile oil of mustard, 4; camphor, 6; castor oil, 14; alcohol, 86. Add the oils to a solution of the camphor in the alcohol, and mix by shaking. Liniment of mustard is a powerful counter-irritant and rubefacient, applied externally in pleurisy and pneumonia, or to relieve deep-seated pain.
- Linimentum Sinapis Compositum, B.P. 1885.—COMPOUND LINIMENT OF MUSTARD.
- Volatile oil of mustard, 2.8; ethereal extract of mezereon, 2; camphor, 6 castor oil, 14; rectified spirit, 88.
The British Pharmaceutical Codex, 1911, was published by direction of the Council of the Pharmaceutical Society of Great Britain.