Kinetics and Mechanism of the Oxidation of Substituted Benzaldehydes by N-Bromobenzamide

Article abstract of DOI:10.1021/jo00375a004

The oxidation of eighteen meta- and para-substituted benzaldehydes by N-bromobenzamide (NBB), to the corresponding benzoic acid, is first order with respect to the aldehyde, NBB, and hydrogen ion.The oxidation of benzaldehyde exhibited a substantial primary kinetic isotope effect(k_H/k_D = 5.3 +/- 0.1).Addition of benzamide has no effect on the reaction rate. (PhCONH2Br)⁺ has been postulated as the reactive oxidizing species.The rates of the oxidation of meta- and para-substituted benzaldehydes were separately correlated in Taft's and Swain's dual substituent parameter equations.For para-substituted aldehydes, the best correlation was obtained with ?₁ and ?_R⁺ values, while meta-substituted compounds correlate with ?₁ and ?_R⁰ values.The reaction constants have negative values.A mechanism involving transfer of a hydride ion from the aldehyde to the oxidant, in the rate-determining step, has been proposed.