Kinetics and mechanism of the oxidation of formic and oxalic acids by benzimidazolium dichromate

Department of Chemistry, J. N. V. University, Jodhpur-342 005, Rajasthan, India

E-mail : seemakothari23@gmail.com, profskothari@gmail.com

Manuscript received 25 May 2011, accepted 16 December 2011

The oxidation of formic and oxalic acids by benzimidazolium dichromate (BIDC), in dimethyl sulfoxide, leads to the formation of carbon dioxide. The reaction is first order with respect to BIDC. Michaelis-Menten type kinetics were observed with respect to the organic acids. The values of the formation constants of the organic acid-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 reaction rate increases with an increase in hydrogen-ion concentration and the dependence has form : k_obs = a + b [H⁺], The oxidation of deuteriated formic acid indicated the presence of a substantial kinetic isotope effect. The reaction has been studied in nineteen organic solvents. An analysis of the solvent effect by solvatochromic equations indicated that though both the anion- and cation-solvating powers of the solvent contribute to the observed solvent effect, however, the role of cation-solvation is more. Suitable mechanisms have been proposed.