Reactivity of Benzyl Alcohol and Substituted Benzyl Alcohols with 1-Chlorobenzimidazole in Acid Medium – A Kinetic and Mechanistic Approach

Abstract

The kinetics of oxidation of benzyl alcohol and a few substituted benzyl alcohols with 1-chlorobenzimidazole (CBI) were studied in aqueous acetic acid medium. The order of the reactions with respect to each oxidant and substrate was found to be unity. The added HClO₄ increases the rate and the order in [HClO₄] was found to be fractional. The reactions were catalyzed by NaCl and a fractional order dependence was observed for [NaCl]. The ionic strength had negligible influence on the rate. Increase in the percentage of acetic acid increases the rate. Addition of benzimidazole, one of the products does not affect the rate. Effect of temperature on the reaction rates was studied at different temperatures and the various activation and thermodynamic parameters were computed. The Hammett plot shows an excellent correlation with negative ρ value (- 0.37) for benzyl alcohols. Product analysis shows the formation of aldehydes as major products of oxidation of benzyl alcohols. CBIH⁺ has been postulated as the reactive oxidizing species. Suitable mechanism and the rate law in consistent with the experimental results have been proposed.