Allyl isothiocyanate, sources

Heating or irradiating alkenes in the presence of sulfur gives relatively low yields of thiiranes. For example, a mixture of sulfur and norbornadiene in pyridine-DMF-NHa at 110 °C gave a 19% yield of the monoepisulfide of norbornadiene as compared with a 78% yield by the method of Scheme 120 (79JCS(Pi)228). Often 1,2,3-trithiolanes are formed instead of thiiranes. The sesquiterpene episulfides in the essential oil of hops were prepared conveniently by irradiation of the terpene and sulfur in cyclohexane (Scheme 135) (80JCS(Pl)3li). Phenyl, methyl or allyl isothiocyanate may be used as a source of sulfur atoms instead of elemental sulfur. 

The u-alkenyl isothiocyanates, except for allyl isothiocyanate, were prepared by the isomerization of the corresponding w-alkenyl thiocyanates 17). The u-alkenyl isothiocyanates were converted to the corresponding w-methylthioalkyl isothiocyanates 18). The other isothiocyanates were purchased from commercial sources and purified by vacuum distillation. 

Crude (whole, ground) and volatile oil. Brown and black mustards were formerly official in N.F. and U.S.P. Mustard oil (volatile oil) formerly official in U.S.P. and currently official in F.C.C. where it is listed as equivalent to synthetic allyl isothiocyanate, except that its source (natural or synthetic) has to be indicated on the label. It is only required that volatile mustard oil or synthetic allyl isothiocyanate contain 93% (or more) allyl isothiocyanate (C3H5NCS) the remaining can be minor amounts of mosly known isothiocyanates (natural mustard oil) or impurities of unknown composition (synthetic allyl isothiocyanate) that can vary with the synthetic processes. 

For example, heating a-naphthyl isocyanate with phenyl isothiocyanate affords phenyl isocyanate . Tolylene diisocyanate (TDI) can be used as a higher-boiling isocyanate source. Thus, heating TDI with allylisothiocyanate affords allyl isocyanate. ... 

---