OXIDATION OF L-ASPARTIC ACID AND L-GLUTAMIC ACID BY MANGANESE(III) IONS IN AQUEOUS SULFURIC-ACID, ACETIC-ACID, AND PYROPHOSPHATE MEDIA - A KINETIC-STUDY

Kinetics of oxidation of L-aspartic acid and L-glutamic acid by mangan ese(III) ions have been studied in aqueous sulphuric acid, acetic acid , and pyrophosphate media. Manganese(III) solutions were prepared by k nown electrolytic/chemical methods in the three media. The nature of t he oxidizing species present in manganese(III) solutions was determine d by spectrophotometric and redox potential measurements. The reaction shows a variable order in [manganese(III)](o): the order changes from two to one as the reactive oxidizing species changes from an aquo ion ic form to a complex form. There is a first-order dependence of the ra te on [amino acid], in all the three media while the other common feat ures include an inverse dependence each on [H+] and on [manganese(II)] . Effects of varying ionic strength and solvent composition were studi ed. Added anions such as pyrophosphate, fluoride, or chloride alter th e reaction rate and mechanism by changing the formal redox potential o f Mn(III)-Mn(II) couple. Activation parameters have been evaluated usi ng the Arrhenius and Eyring plots. Mechanisms consistent with the kine tic data have been proposed and discussed. (C) 1995 John Wiley and Son s, Inc.