Oxidation reactions of a system composed of chloro(5,10,15,20-tetraphenylporphyrinato)cobalt(III) and its .PI. cation radical with phenols.

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The reactions of a system composed of chloro(5,10,15,20-tetraphenylporphyrinato)cobalt(III), [CoIIICl(tpp)], and its π cation radical coordinating axially two chloride anions, [CoIII(tpp)+·]Cl2, with several phenols were investigated by using ESR and optical absorption spectroscopy. The phenols were oxidized to phenoxyl radicals. The phenols investigated were classified into two groups after taking into account the differences in the reaction activities and their redox potentials, the phenols mainly reacting with [CoIII(tpp)+·]Cl2 and those reacting with both [CoIIICl(tpp)] and [CoIII(tpp)+·]Cl2. The oxidation reactions of phenols with [CoIII(tpp)+·]Cl2 were the second-order. A linear relationship between the rate constants of oxidation and the redox potentials of phenols was recognized. Active species in the reactions were determined to be composed of a chlorine radical which originates from axial ligands of [CoIIICl(tpp)] and [CoIII(tpp)+·]Cl2, and the porphyrin ligand of [CoIII(tpp)+·]Cl2 itself. A possible mechanism for the oxidation reactions is proposed. Finally, the reaction scheme of cobalt porphyrin, ([CoII(tpp)], [CoIIICl(tpp)], and [CoIII(tpp)+·]Cl2) with phenols is compared with oxidation reactions of phenols with horseradish peroxidase.
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