Kinetic Studies of Oxygen Exchange and Racemization Reactions of Diaryl Sulfoxides in Sulfuric Acid of Various Concentrations

Abstract

Abstract When 18O-labeled and optically active sulfoxides are dissolved in a concentrated sulfuric acid, one observes the concurrent oxygen exchange and racemization reactions of the sulfoxides, and these reactions were found to proceed through the SN1-like path (S. Oae et al., Bull. Chem. Soc. Japan, 38, 546 (1965); 41, 696 (1968)). We have found that the concurrent oxygen exchangeand racemization reactions also take place even in less concentrated sulfuric acid at somewhat higher temperature, i. e. 70% sulfuric acid at 30°C, and proceed through a different mechanistic route, very likely an SN2-like path. Kinetic investigation on these reactions in sulfuric acid of various concentrations (66.5–96.3%) suggests there is a gradual change of mechanism of the reaction, i. e. from SN2 type in 66.5% to SN1 type in 96.3% with the increase of the concentration of sulfuric acid.