Reaction of Sulfoxides with Acylating Reagents. II. Mechanism of the Reactions of Aryl Benzyl Sulf oxides with Acetic Anhydride

Aryl benzyl sulfoxides undergo oxygen exchange and racemization reaction with acetic anhydride, and the rate is dependent on the concentration of both the sulfoxide and acetic anhydride. The reaction proceeds faster in a more polar solvent. Addition of sodium perchlorate or acetic acid accelerates the reaction. In this case, the rate of oxygen exchange is not exactly half of that of racemization. As an example, the ratio, kex/krac, is 0.36 when the reaction was carried out at 100°C. Under the same condition, both the Pummerer reaction and thermal racemization are negligible. Similar to diaryl sulfoxides the effects of phenyl group are small. Implication of the ratio is discussed.