Kinetics and mechanism for the oxidation of anilines by ClO2: a combined experimental and computational study

The oxidation of para-substituted anilines (X-C6H4NH2, X=-CH3, -H, -Cl, -NO2) with chlorine dioxide was studied as a means of eliminating these pollutants. The oxidation rate decreases from that for 4-methylaniline to that for 4-nitroanilinem in agreement with the Hammett plot; the oxidation kinetics is second order in aniline and first order in ClO2, for which a possible mechanism is proposed. Liquid chromatography and gas chromatography mass spectrometry results show that benzoquinone is formed as the major intermediate in aniline/ClO2 oxidation, and the reaction is pH-dependent as the rate constant increases with increasing pH. To further support our proposed mechanism, Density Functional Theory (DFT) computations at both B3LYP/6-311+G(d,p) level with the polarizable continuum model with an integral equation formalism solvation model (i.e., with water) were carried out, showing that activation energy barriers predict the same reactivity trend as shown by the kinetics experiments. Copyright (c) 2014 John Wiley & Sons, Ltd.