OXYGENATION REACTION OF ORGANIC SULFIDES WITH OXOCHROMIUM(V) ION

The selective oxidation of 19 alkyl aryl sulfides to sulfoxides with t hree oxochromium(V) complexes in an acetonitrile-water mixture is over all second order, first order in the oxidant and in the substrate. Sul fides containing electron-attracting substitutents retard the rate whi le those containing electron-releasing substitutents accelerate the ra te of oxidation. The rate constant for the oxygenation reaction, k(2), is better correlated with sigma(+)/sigma(-) than Hammett sigma consta nts. The reactivity of different alkyl phenyl sulfides C6H5SR (R = Me, Et, n-Pr, i-Pr, n-Bu, and t-Bu) is accounted for in terms of Taft's p olar, sigma, and steric, E-s, substitutent constants. These kinetic r esults 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) oxida tion.