Comparative Study of Chromium(V) and Chromium(VI) Oxidation of Dialkyl Sulfides

The kinetics of the redox reaction of dialkyl sulfides, model compounds for methionine containing peptides, with CrV and CrVI has been studied spectrophotometrically in aqueous CH3CN. Both reactions follow overall second-order kinetics, first order each in sulfide and oxidant. The rate of the reaction with CrV is two orders more than CrVI. Based on the substituent and solvent effect an outer-sphere electron transfer mechanism has been proposed for CrV oxidation. Two different mechanisms, one involving nucleophilic attack of sulfide on chromium and the other, an electron transfer from sulfide to Cr, has been proposed for the CrVI oxidation.