Kinetics and mechanism of 2,6-dimethyl-aniline degradation by hydroxyl radicals

This research investigated the intrinsic second-order rate constant between 2,6-dimethyl-aniline (2,6-DMA) and hydroxyl radicals (OH center dot) using Fenton's reactions under both batch and continuous operations. The competitive kinetics technique with aniline as a reference compound was employed. In the batch study under various conditions, the second-order rate constants of 2,6-DMA with OH center dot were between 1.59 x 10(10) and 1.80 x 10(10) m(-1) s(-1) with a mean of 1.71 x 10(10) m(-1) s(-1) which equals the average value obtained from the continuous study as well. The concentrations of OH center dot at the steady state under the continuous mode were estimated to be between 4.85 x 10(-10) and 6.82 x 10(-10) mM. 2,6-dimethyl-nitrobenzene, 2,6-dimethyl-phenol, 2,6-dimethyl-nitrophenol, 2,6-dimethyl-hydroquinone, 2,6-dimethyl-p-benzoquinone, and 2,6-dimethyl-3-hydroxy-p-benzoquinone were identified as the aromatic by-products indicating that the methyl group on the aromatic ring was not susceptible to OH center dot attack. Maleic, lactic, oxalic, acetic, and formic acids were found as generated carboxylic acids. An oxidation pathway of 2,6-DMA by OH center dot is also proposed. (C) 2009 Elsevier B.V. All rights reserved.