Effect of substituents on the rate of oxidation of anilines with peroxomonosulfate monoanion (HOOSO−3) in aqueous acetonitrile: A mechanistic study

Mechanistic studies on the oxidation of 18 meta-, para-, and ortho-substituted anilines (Ans) by HOOSO3- in aqueous acetonitrile medium have been performed. The reaction can be characterized by the experimental rate equation. -dHSO5-]/dt = kAn] vertical bar HSO(5)(-)vertical bar The addition of p-toluenesulfonic acid (TsOH) retards the reaction. The increase in the reactivity of anilines as the medium is made more aqueous is interpreted. The reaction is enhanced by electron-donating groups on the amine in the series consistent with the rate-limiting nucleophilic attack of the amine on the persulfate oxygen. The proposed mechanism involves the conversion of phenylhydroxylamine to nitrosobenzene in a fast step. The ESR study reveals the absence of free radicals in the reaction. Various attempts have been made to analyze the experimental rate constants in terms of LFER plots. Improved correlations are obtained with a values and the sigma- form of the Yukawa-Tsuno equation. (c) 2005 Wiley Periodicals, Inc.