Oxidation of l-asparagine by bis(hydrogenperiodato)argentate(III): a kinetic investigation

Abstract

The kinetics of oxidation of l-asparagine by bis(hydrogenperiodato)argentate(III) complex anion ([Ag(HIO6)2]5−) has been studied in the temperature range of 10.0–25.0 °C in aqueous alkaline media. An overall second-order character is observed, the reaction being first order with respect to both Ag(III) and Asn. The observed second-order rate constants $$ k^{{\prime }} $$ are increased when [OH−] is increased, but are decreased with increasing total concentration of periodate, [IO 4 − ]tot. The oxidation results in both decarboxylation and deamination of Asn. A reaction mechanism is proposed which involves two pre-equilibria leading to an intermediate complex [Ag(HIO6)(Asn)(OH)]3−. This is followed by the collapse of the intermediate in two parallel reaction paths as the rate-determining steps; one path is independent of OH−, while the other involves OH−. The rate equation has been derived from the reaction mechanism, and the equilibrium constants and rate parameters have been evaluated. The mode of electron transfer is discussed. The reaction mechanism and electron transfer mode in the present system have no similarities to those derived for the oxidations of Asn by other oxidants reported previously, underlining the diverse nature of Asn oxidations.