Search for general acid catalysis in the reduction and racemization of sulphoxides

Abstract

The iodide ion reduction of methyl p-tolyl sulphoxide and the chloride ion racemization of isopropyl phenyl sulphoxide have been studied in aqueous perchloric acid and in sulphuric acid. The rates of the former reaction in the two acids are similar. This, and the form of dependence of the rates on acidity, suggest specific acid catalysis. The rate of racemization of isopropyl phenyl sulphoxide is greater in sulphuric than in perchloric acid and the dependence on acidity suggests a gradual shift toward general acid catalysis. The appearance of general acid catalysis with branching of the alkyl group is discussed in relation to general mechanisms for the reduction and racemization of sulphoxides.