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) 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 were between 1.59 × 1010 and 1.80 × 1010 M−1 s−1 with a mean of 1.71 × 1010 M−1 s−1 which equals the average value obtained from the continuous study as well. The concentrations of OH at the steady state under the continuous mode were estimated to be between 4.85 × 10−10 and 6.82 × 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 attack. Maleic, lactic, oxalic, acetic, and formic acids were found as generated carboxylic acids. An oxidation pathway of 2,6-DMA by OH is also proposed.