Cooxidation of anilides and oxalic acid by chromic acid: A one-step, three-electron oxidation

Abstract

The chromic acid oxidation of a mixture of oxalic acid and anilides proceeds much faster than that of either of the two substrates alone. The oxidation kinetics of acetanilide, p-methyl-, p-chloro-, and p-nitroacetanilides by Cr(VI) in the presence of oxalic acid in aqueous acetic acid medium follows first-order, zero-order, and second-order dependence in [oxidant], [substrate], and in [oxalic acid], respectively, while the oxidation kinetics of benzanilide, p-methyl-, p-chloro-, and p-nitrobenzanilides follow first order in [oxidant] and fractional order each in [substrate] and [oxalic acid] and yields corresponding azobenzenes and benzaldehydes in the case of benzanilide and substituted benzanilides as the main products of oxidation. Aluminium ions suppress the reaction. The intermediate is believed to be formed from the anilide and a chromic acid-oxalic acid complex. In the proposed mechanism, the rate-limiting step involves the direct reduction of Cr(VI) to Cr(III). © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 33: 21–28, 2001