The kinetics of cooxidation of several substituted phenyl methyl sulfoxides and oxalic acid with Cr (VI) have been carried out in the presence of perchloric acid. The reaction is first order each in sulfoxide, oxalic acid, Cr (VI), and H+. The products of oxidation are sulfones and carbon dioxide. Electron-releasing groups in the phenyl ring accelerate the rate while electron-withdrawing groups retard it. The Hammett correlation yields a reaction constant ...