Base-catalyzed oxidation of L-asparagine by alkaline permanganate and the effect of alkali metal ion catalysts: a kinetic and mechanistic approach

Kinetic investigations on the oxidation of l-asparagine (Asn) by alkaline permanganate have been carried out spectrophotometrically at a constant ionic strength and temperature. The reaction is first order with respect to [MnO4 (-)] and less than unit order with respect to both [Asn] and [alkali]. The influence of pH indicated that the oxidation is base catalyzed. The reaction rate was found to increase with increasing ionic strength and temperature. The addition of alkali metal ion catalysts accelerates the oxidation rate. The proposed reaction mechanism involves the formation of a 1:1 intermediate complex between l-asparagine and an alkali-permanganate species in a pre-equilibrium step, which was confirmed by both spectral and kinetic evidence. The complex decomposes slowly in a rate determining step, resulting in the formation of a free radical. The latter reacts again with another alkali-permanganate species in a subsequent fast step to yield the final reaction products which were identified as aldehyde (alpha-formyl acetamide), ammonia, manganate(VI) and carbon dioxide. The appropriate rate laws are deduced. The reaction constants involved in the mechanism were evaluated. The activation and thermodynamic parameters were determined and discussed.