A Kinetic andMechanistic Study of 2,2'- Bipyridyl the Catalyzed Chromium(VI) Oxidation of Lactic Acid

The kinetics and mechanism of 2,2′-bipyridyl (bpy) catalysis of the chromium(VI) oxidation of lactic acid (Lac) in aqueous acidic medium was studied with spectrophotometry in a temperature range of 25∼40 ◦C. The reaction was found to be pseudo-first order with respect to Cr(VI) and first order to lactic acid. It was found that the pseudo-first order rate constantkobs increased with the increase in [H+] and [bpy]. There is a weak negative salt effect and no free radicals are detected. Thus, HCrO4 is assumed the main existing species of Cr(VI). Based on the experimental results, a probable reaction mechanism of oxidation is proposed. The rate equation derived from the mechanism can explain all the experimental phenomena. The activation parameters, along with rate constants of the rate-determining step, have been calculated.