Oxygenation Reaction of Organic Sulfides with Oxochromium(V) Ion

Abstract

The selective oxidation of 19 alkyl aryl sulfides to sulfoxides with three oxochromium(V) complexes in an acetonitrile-water mixture is overall second order, first order in the oxidant and in the substrate. Sulfides containing electron-attracting substitutents retard the rate while those containing electron-releasing substitutents accelerate the rate of oxidation. The rate constant for the oxygenation reaction, k(2), is better correlated with sigma(+)/sigma(-) than Hammett sigma constants. The reactivity of different alkyl phenyl sulfides C(6)H(5)SR (R = Me, Et, n-Pr, i-Pr, n-Bu, and t-Bu) is accounted for in terms of Taft's polar, sigma, and steric, E(s), substitutent constants. These kinetic results are interpreted in terms of a mechanism involving outer sphere electron transfer from sulfide to Cr(V) as the rate-determining step. The results of Cr(V) oxidation are compared with those of Cr(VI) oxidation.