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 K3) were obtained in good yields by oxidation of 2,3,6-trimethylphenol and 2-methyl-1-naphthol, respectively, with tBuOOH catalyzed by supported iron tetrasulfophthalocyanine. The mechanism of this heterogeneous oxidation was studied using 18O2labeling experiments, EPR spectroscopy with spin traps, kinetic studies, and complete analysis of reaction products including minor ones. 18O2labeling experiments did not indicate the involvement of O2 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.