Kinetics and mechanism of Os(VIII)‐catalyzed hexacyanoferrate(III) oxidation of α amino acids in alkaline medium

Abstract

AbstractThe kinetics of the Os(VIII)‐catalyzed oxidation of glycine, alanine, valine, phenylalanine, isoleucine, lycine, and glutamic acid by alkaline hexacyanoferrate(III) reveal that these reactions are zero order in hexacyanoferrate(III) and first order in Os(VIII). The order in amino acid as well as in alkali is 1 at [amino acid] ⩽2.5 × 10−2M and [OH−] ⩽1.3 × 10−M, but less than unity at higher concentrations of amino acids or alkali. The active oxidizing species under the experimental conditions is OsO4(H2O) (OH)−. The ferricyanide is merely used up to regenerate the Os(VIII) species from Os(VI) formed during the reaction. The structural influence of amino acids on the reactivity has been discussed. The amino acids during oxidation are shown to be degraded through intermediate keto acids. The kinetic data are accommodated by considering the interaction between the conjugate base of the amino acids and the active oxidizing species of Os(VIII) to form a transient complex in the primary rate‐determining step. The catalytic effect of hexacyanoferrate(II) has been rationalized.