Aromatic Hydroxylation with an Iron(III)–Catechol–H2O2 System. Mechanistic Implication of the Role of Catechol

The role of catechol in benzene hydroxylation with Fe3+/catechol/H2O2 system, the so-called Hamilton system, has been mechanistically investigated by using tiron as a substitute for pyrocatechol. The yield of phenol progresses linearly with reaction time. The phenol yield is dependent on the mole ratio of Fe3+ relative to tiron, and the ratio of more than unity is particularly important for the effective functioning of the catalyst system. The o-, m-, and p-product isomer distributions for a few aromatic hydrocarbons are nearly identical with those of the Fenton reaction. These and the separate experimental results are consistent with the mechanism involving the rate-limiting redox reaction between tiron and Fe3+ and then the follow-up radical chain sequence as in the Fenton reaction.