Kinetics and mechanism of oxidation of amino acids by chloramine-T in aqueous acid medium

The kinetics of oxidation of amino acids (AA) - leucine, serine, aspargine, glutamine, glutamic acid and proline, by chloramine-Tr have been investigated in aqueous medium over a wide [HClO4] range (0.0005 to 0.10moldm(-3)). The rate - [H+] plots exhibit bell-shaped profiles. Oxidations at [HClO4]> 0.005moldm(-3) show second order kinetics in [CAT] and first order at [HClO4] less than or equal to 0.002moldm(-3). The reactions at high and low [HClO4] are generally of fractional order in [AA] and the inverse order in [AA], respectively. Variation in ionic strength of the medium or addition of toluene-p-sulphonamide has no significant effect on the rates. The rates decrease with the decrease in dielectric constant of the medium. The results are explained on the basis of a two-pathway mechanism. Activation parameters corresponding to both the pathways have been calculated. The rate constants have also been recalculated from the deduced rate laws as [H+] is varied, which are in a good agreement with the experimental constants. The isokinetic relationships are found to be valid for both the pathways, with isokinetic temperatures of 289K and 340K, respectively. The amino acids alanine, valine and phenyl alanine, studied in the narrow [HClO4] range earlier, have also been reinvestigated under the present reaction conditions for the purpose of generalizing the mechanism. The applicability of the Taft equation has also been tested.