Thiocyanation of alkyl halides with alkyl thiocyanates in the presence of quaternary phosphonium halides

Abstract

Alkyl thiocyanates undergo simple S_N2 reactions with the counter ions of quaternary phosphonium salts in nonpolar solvents and thiocyanate ions are liberated as the leaving ion. Depending on the nucleophile, the reaction proceeded irreversibly or reversibly. The reaction of benzyl thiocyanate with azide ions afforded a quantitative yield of benzyl azide. The reactions of alkyl thiocyanates with halide ions gave an equilibrium mixture where the reverse reaction of the alkyl halides produced with the liberated thiocyanate ions took place simultaneously. Thus, thiocyanate–halide exchange reactions between an alkyl thiocyanate and an alkyl halide were possible in the presence of a catalytic amount of a quaternary salt.