The kinetics of permanganate oxidation of P-phenylalanine in aqueous perchlorate media at a constant ionic strength of 3.0 mol dm-3 has been studied spectrophotometrically. A first-order reaction in [MnO,] and a fractional order with respect to P-phenylalanine were observed. The results obtained at various hydrogen-ion concentrations indicate that the protonated species of both the amino acid and permanganate play a role in the kinetics. Kinetic evidence for the formation of an intermediate complex between the amino acid and the oxidant is presented. The activation parameters were calculated and found to be ASs = -1 60.1 4 8.23 J K-l mol-l, AHs = 34.04 f 1.02 k J mol-l, and AG' = 81.77 f 3.47 k J mol-l, respectively. A mechanism consistent with the kinetic results is discussed.Permanganate ion in acidic media has been used extensively as a potent oxidant for studying the oxidation kinetics of many organic substrates including amino acids.'-7 In some cases the mechanistic approach has been based on intermediate complex formation and in others the results have been interpreted by a free-radical mechanism, in the absence of kinetic or spectrophotometric evidence. The mechanisms suggested by various authors are not uniform, indicating that a wide variety of mechanisms is possible depending on the nature of the reactive species of permanganate as well as of the amino acids.

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