The oxidation of 2,3,6-trimethylphenol with Fenton's reagent has been investigated under mild conditions in aqueous phase. 2,3,5-Trimethylbenzoquinone was obtained with a selectivity of nearly 99.9% at 100% conversion of 2,3,6-trimethylphenol at 45 degrees C for 3 h. The different parameters like: the performance of different catalysts, the effect of catalyst concentration, reaction time, and reaction temperature has been investigated. Moreover, our new catalytic system was found also to be active in the oxidation of o-methylphenols to the corresponding benzoquinones by 5% H2O2 under mild conditions. In order to further study this reaction system, the possible mechanism was proposed. An important advantage of this catalytic system, apart from the organic solvent-free conditions, is that it is nontoxic, inexpensive and water-soluble. (C) 2008 Elsevier B.V. All rights reserved.