Mechanistic Study of Air Oxidation of Benzene in Sulfuric Acid Catalyzed by Cuprous Ions

Article abstract of DOI:10.1021/jo00368a013

The aerial oxidation of benzene in a 0.05 M H2SO4 solution in the presence of CuCl produces phenol and hydroquinone, the latter of which is not found in Fenton reactions.The present study was carried out for elucidation of the mechanism of the reaction in the presence of Cu⁺ ions by the aid of 18O-tracer technique.Results obtained are consistent with the reaction mechanism of the Fenton reaction currently accepted, and no peculiar mechanism inherent to Cu⁺ ions is observed.The isotope incorporation in both phenol and hydroquinone was in good agreement with thesimple probability rule as if there was no isotope scrambling during the whole reaction sequence.This is in accordance with the mechanism in which hydroquinone is derived from the oxygen adduct of a hydroxycyclohexadienyl radical almost exclusively.Under our conditions, however, equilibration between hydroxycyclohexadienyl radicals and benzene cation radicals is not observed, presumably because the latter, if formed, are rapidly reduced by Cu⁺ ions.