Kinetics and structure reactivity correlation in the oxidation of some para- substituted benzhydrols by benzimidazolium dichromate

Abstract

The oxidation of some para-substituted benzhydrols by benzimidazolium dichromate (BIDC) in dimethyl sulfoxide (DMSO) medium, results in the formation of corresponding diphenyl ketone. The reaction has been investigated on the condition of pseudo-first order. In terms of both BIDC and hydrogen-ion, the reaction is first order. In the case of benzhydrols, however, Michaelis-Menten type kinetics is observed. At different temperatures, the formation constants and rates of breakdown of benzhydrol-BIDC complexes have been determined. Complex formation thermodynamic parameters and activation parameters for complex decomposition have been computed. The kinetic isotope effect found in the oxidation of benzhydrol ((kH/kD = 5.93 at 293 K) shows that the rate-determining step involved α-C-H bond fission. For the kinetic analysis of the reaction, nineteen organic solvents have been utilized. The solvent impact have been investigated, and found that cation-solvation plays a significant role. A suitable mechanism is proposed based on the kinetic data, solvent effect analysis, and results of various non-kinetic parameters.