Allyl sulfocyanate

Allyl sulfocyanate—Essential oil of mustard—Oleum sinapis... 

At temperatures above 40° (104° F.) myrosin becomes coagulated and incapable of decomposing potassium myronate, a. change which is also produced by contact with acetic acid. Aa the rubefacient and vesicant actions of mustard when moistened with HaO, are due to the prod action of allyl sulfocyanate, neither-vinegar, acetic acid, nor heat greater than 40° (104° F.) should be used in the preparation of mustard cataplasms. 

Pure allyl sulfocyanate is a transparent, colorless oil sp. gr., 1.015 at 20° (68° F.) boils at 143° (289°.4 F.) has a penetrating, pungent odor, sparingly soluble in HaO, very soluble in alcohoL and ether. When exposed to the light it g radually turns brownish-yellow and deposits a resinoid material. When applied to-the skin it produces rubefaction, quickly followed by vesication,. 

In practice the powdered cake of black-mustard seeds, from which the fixed oil has been expressed, is digested with HaO for 34 hours, after which the HaO is distilled as long as any oily matter passes over the oil is collected, dried by contact with calcium chlorid, and redistilled. Essence of mustard may also be obtained synthetically by the action of allyl bromid or iodid upon potassium sulfocyanate, or by the action of allyl iodid upon silver sulfocyanate. 

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