Substituent Effect in o-Nitroperbenzoic Acid Oxidation of m- and p-Substituted Acetophenones

Abstract

Abstract The Baeyer–Villiger reaction of m- and p-substituted acetophenones (substituents: H, p-MeO, p-t-Bu, p-i-Pr, p-Et, p-Me, p-Cl, p-Br, m-MeO, m-Me, m-Cl) with o-nitroperbenzoic acid was studied in chloroform at 30°C. The rate constants for the general acid catalysis were measured at several concentrations of o-nitrobenzoic acid which acted as an acid catalyst. The uncatalyzed and acid-catalyzed rate constants obtained afforded ρ values of −2.16 and −4.11 with σ, respectively. The results indicated that the rate-determining step is the migration of the phenyl group in the peroxy acid-carbonyl adduct for all the substituents studied, whether the reaction is acid-catalyzed or not, and that the acid catalyst intervenes only in the formation of the acid-ketone adduct in the initial state and not in the migration step. The variation of the leaving group abilities required the variation of the substituent constants applied, whereas the acid intervention in the addition step was reflected only in the variation of the ρ value, not in the substituent constants to be applied. The smaller resonance demand for o-nitroperbenzoic acid indicated that the structure of the transition state in the migration step was looser and that the position of the transition state was earlier than those for m-chloroperbenzoic acid.