Steric and pH Effects on the Rate of Dakin Oxidation of Acylphenols

Article abstract of DOI:10.1021/jo00143a007

The rates of hydrogen peroxide oxidation of a series of o- and p-acylphenols with a variety of aliphatic substituents on the carbonyl carbon have been measured over a range of alkaline pH conditions. p-Hydroxypivalophenone was here synthesized for the first time, to complete this series.Relative rates of Dakin oxidation appear to be more strongly affected by the bulk of the aliphatic carbonyl substituent than those found for parallel alkaline ester hydrolyses and somewhat less strongly than those forperbenzoic acid oxidations.Correlations of oxidation rate with pH show a double maximum and a high rate throughout the pH range 9.5-13.5 for o-hydroxyacetophenone and a single maximum of about half the ortho rates over the narrower pH range of 11.5-13.5 for p-hydroxyacetophenone.Unimolecular involvement of undissociated hydrogen peroxide in the rate-determining step of the lower pH maximum for o-hydroxyacetophenone and of hydroperoxide anion in the high-pH maximum for both o- and p-hydroxyacetophenone is one explanation consistent with the observed results.