1911 Encyclopædia Britannica/Mustard Oils

MUSTARD OILS, organic chemical compounds of general formula R·NCS. They may be prepared by the action of carbon bisulphide on primary amines in alcoholic or ethereal solution, the alkyl dithio-carbamic compounds formed being then precipitated with mercuric chloride, and the mercuric salts heated in aqueous solution,

2R·NH2	CS2	CS	NHR	HgCl2	[RHNCS2]2Hg→HgS+H2S+2RNCS,
	→		S·NH3R	→

or the isocyanic esters may be heated with phosphorus pentasulphide (A. Michael and G. Palmer, Amer. Chem. Jour., 1884, 6, 257). They are colourless liquids with a very pungent irritating odour. They are readily oxidized, with production of the corresponding amine. Nascent hydrogen converts, them into the amine, with simultaneous formation of thio-formaldehyde, RNCS+4H＝R·NH₂+HCSH. When heated with acids to 100° C, they decompose with formation of the amine and liberation of carbon bisulphide and sulphuretted hydrogen. They combine directly with alcohols, mercaptans, ammonia, amines and with aldehyde ammonia.

Methyl mustard oil, CH₃NCS, melts at 35° C. and boils at 119° C. Allyl mustard oil, C₃H₅NCS, is the principal constituent of the ordinary mustard oil obtained on distilling black mustard seeds. These seeds contain potassium myronate (C₁₀H₁₈NS₂O₁₀K) which in presence of water is hydrolysed by the myrosin present in the seed,

C₁₀H₁₈NS₂O₁₀K＝C₆H₁₂O₆+KHSO₄+C₃H₅NCS.

It may also be prepared by heating allyl sulphide with potassium sulphocyanide. It is a colourless liquid boiling at 150·7° C. It combines directly with potassium bisulphite. Phenyl mustard oil C₆H₅NCS, is obtained by boiling sulphocarbanilide with concentrated hydrochloric acid, some triphenylguanidine being formed at the same time. It is a colourless liquid boiling at 222° C. When heated with copper powder it yields benzonitrile.