Kinetics and mechanism of the oxidation of alkyl substituted phenols and naphthols with tBuOOH in the presence of supported iron phthalocyanine

2,3,5-Trimethylbenzoquinone (precursor of vitamin E) and 2-methylnaphthoquinone (vitamin K-3) were obtained in good yields by oxidation of 2,3,6-trimethylphenol and 2-methyl-1-naphthol, respectively, with (BuOOH)-Bu-t catalyzed by supported iron tetrasulfophthalocyanine. The mechanism of this heterogeneous oxidation was studied using O-18(2) labeling experiments, EPR spectroscopy with spin traps, kinetic studies, and complete analysis of reaction products including minor ones. O-18(2) labeling experiments did not indicate the involvement of O-2 in the oxidative process. EPR study of reaction mixtures of 2,3,6-trimethylphenol and 2-methyl-1-naphthol oxidations in the presence of 3,5-dibromo-4-nitrosobenzenesulfonic acid spin trap showed no formation of any radical intermediates. Besides the target quinones, epoxyquinones and formyldimethyl-1,4- benzoquinones, as over-oxidation minor products have been found. C-C and C-O coupling products relevant to one-electron oxidation pathways were detected in trace amounts. Based on the experimental results, a mechanism of oxidation of alkyl-substituted phenols and naphthols mediated by the supported iron phthalocyanine catalyst has been proposed which involves two successive electron transfers without escape of radical species in solution.