Alkyl aryl sulphides from the interaction of aryl thiocyanates and alcohols under the influence of triphenylphosphine or of trialkyl phosphites

Abstract

Typical aryl thiocyanates react with primary alcohols in the presence of triphenylphosphine to give hydrogen cyanide, triphenylphosphine oxide, and the corresponding alkyl aryl sulphide in high yield. With propan-2-ol, yields of sulphide are lower on account of the competing elimination reaction which leads to a benzenethiol and propene. t-Butyl alcohol yields exclusively products of elimination. Alcohols in the presence of their phosphite esters give similar results, even with p-dimethylaminophenyl thiocyanate, the one thiocyanate studied that failed to give alkyl aryl sulphide with triphenylphosphine and simple primary alcohols. It is suggested that the observed products arise from collapse of a triphenyl- or trialkoxy-oxythiophosphorane which results from attack of an alcohol molecule on the first-formed triphenyl- or trialkoxy-arylthiophosphonium cyanide.