Add time:09/05/2019         Source:sciencedirect.com

The kinetics of the ruthenium(III) chloride [Ru(III)]-catalysed oxidation of four α-amino acids (AA) viz. glycine (Gly), valine (Val), alanine (Ala) and leucine (Leu) by sodium N-chloro-p-toluenesulfonamide (CAT: Chloramine-T) in the presence of hydrochloric acid medium has been studied at 308 K. The oxidation reaction follows the identical kinetics for all the four amino acids and obeys the rate law, rate=k′[CAT]o[S]ox[H+]y[Ru(III)], where x and y are fractions. Variation of ionic strength of the medium, addition of the halide ions and the reaction product (PTS: p-toluenesulfonamide) show negligible effect on rate of the reaction. Solvent composition shows positive effect indicating that positive ion-dipolar molecule involved in the rate determining step. The oxidation products were identified. The activation parameters have been evaluated from the Arrhenius plots. The activation energy values are least for the fastest reactions and vice versa. The large negative value of ΔS‡ and the high value of ΔG‡ support the proposed mechanism. Under comparable experimental conditions, the rate of oxidation of amino acids increases in the order: Leu > Ala > Val > Gly. This trend may be attributed to hydrophobicity, nucleophilicity and inductive effect of amino acids. The reaction mechanism and the derived rate law are consistent with the observed experimental results.

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