Kinetics of peroxodisulphate oxidation of ortho-substituted N,N-dimethylanilines, and the mechanism of Boyland–Sims oxidation

Abstract

The kinetics of oxidation of some ortho-substituted N,N-dimethylanilines by peroxodisulphate have been studied in 50%(v/v) aqueous ethanol containing 0.025 mol dm^–3 phosphate buffer (pH 7). The reaction is second-order overall, and first-order in each reactant. The rate is not influenced by the presence of the free-radical inhibitor allyl acetate. An increase in the polarity of the medium enhances the rate. The reactivities of ortho-substituted anilines lie in the order o-H > Me ∼ MeO > F > Br >Cl > NO₂. Multiple regression analysis of the rate data reveals that the rate is susceptible to significant electronic and steric effects. All these observations are rationalised on the basis of attack of the oxidant at the ipso-position of the amine. Correlation analysis of reactivity data from the literature also indicates that the mechanism involves ipso-attack and not attack on nitrogen.