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Mechanism and Kinetics of the 2,2 Œ-Bipyridyl Catalysis of the Chromium(VI) Oxidation of Malic Acid

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A spectrophotometric study of the kinetics and mechanism of the oxidation of malic acid (Mal) by chromium(VI) catalyzed by 2,2پŒ-bipyridyl (bpy) in aqueous acidic medium was conducted in a temperature range of ~298 to 313 K. This reaction was found to be pseudo-first order with respect to Cr(VI) and first order with respect to malic acid. Under the conditions of the pseudo-first order ([Mal]o >> [Cr(VI)]o ), the observed rate constant (kobs) increased with the increase in [H+] and [bpy]. There was a weak negative salt effect. Based on the experimental results, a possible reaction mechanism for this oxidation catalyzed by bpy is proposed. The rate equation derived from this mechanism can explain all the experimental phenomena.

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