Kinetics and mechanism of the oxidation of furfural by benzimidazolium dichromate under non aqueous medium

The oxidation of furfural (2-furaldehyde), by benzimidazolium dichromate (BIDC) in dimethyl sulfoxide, leads to the formation of 2-furoic acid. The reaction is first order with respect to BIDC and hydrogen-ion. However, Michaelis–Menten type kinetics was observed with respect to furfural. The formation constants of furfural-BIDC complexes and the rates of their decomposition have been evaluated at different temperatures. Thermodynamic parameters of the complex formation and activation parameters for the decomposition of the complexes have been calculated. The deuterium isotope effect observed in the oxidation of furfural (kH/kD = 6.23 at 298 K) indicated an α-C-H bond cleavage in the rate-determining step. The reaction has been studied in 19 organic solvents. The analysis of the solvent effect showed that the role of cation-solvation is major. Based on the kinetic data, analysis of the solvent effect and the result of some non-kinetic parameters, a mechanism involving rate-determining oxidative decomposition of the complex, through hydride-ion transfer via a cyclic transition state, to give the corresponding product is suggested.