Oxidation of 2,3,6-trimethylphenol (TMP) with potassium peroxymonosulfate (KHSO5) catalyzed by iron phthalocyanine tetrasulfonate ([FePcTS]) in an 8-to-1 methanol-water mixture resulted in 43.2-100.0% conversion of TMP and 60.5-100.0% selectivity of trimethyl-1,4-benzoquinone (TMQ) after 5 min at ambient temperature when the oxidant/substrate molar ratio was changed from 1 to 4 at a constant substrate/ catalyst molar ratio of 300. Higher conversion of TMP and selectivity of TMQ were obtained when the reaction time was extended to 30 min. A minor product, 2,2',3,3,5,5'-hexamethyl-4,4'-biphenol (BP), was formed in reactions carried out with an oxidant/substrate molar ratio of 3 or lower. When cobalt phthalocyanine tetrasulfonate ([CoPcTS]) was employed as a catalyst instead of [FePcTS], a slower reaction rate for the oxidation of TMP was observed and the product composition was about the same as that observed in the [FePcTS] catalysis. Oxone, which is a solid consisting of a 2: 1:1 mixture of KHSO5, KHSO4, and K2SO4, was used to introduce KHSO5 into the reaction mixture. (C) 2008 Elsevier B.V. All rights reserved.