Kinetics and mechanism of oxidation of β-phenylalanine by permanganate ion in aqueous perchloric acid

Abstract

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.

Kinetics and mechanism of formation of manganate(VI) and hypomanganate(V) coordination polymer intermediates during the base‐catalyzed oxidation of carboxymethyl cellulose polymer by permanganate, Part 1

“…The above mechanism involves two competitive rate-determining steps (3,4) The observed rapid growth of the blue color and then gradual fading supports that suggestion. Again, the Mn(VI) green intermediate was decomposed much more slowly to the final products of the keto derivative (colorless solution) and MnO 2 .…”

“…It is of interest that the highly negative values of activation entropy S # , for which the authors, in similar cases, postulated the formation of association intermediate complex between MnO 4 − and reductant species [3], were given in Table I and are characteristic of inner sphere one and/or two electron transfer [17].…”

Novel Carboxymethyl Cellulose Ionotropic Gels

“…and [10], [11], in the earlier procedure via the two transient species A 1 , A 2 . Moreover, and according to the above mechanism, the final products are suggested to be the brown MnO 2 precipitate that formed in the bottom of the spectrophotometric cell on ageing and monoketo or diketo derivatives of carboxymethyl cellulose.…”

“…Analyses of the prepared stock solutions of the reagents, as well as kinetic measurements, were carried out using the same procedure as reported before (10).…”

Kinetics and mechanism of oxidation of DL-α-alanine by permanganate ion in acid perchlorate media

“…The mechanism proposed by them could not explain some of the experimental observations. Our preliminary experiments on this reaction at moderate [H+] suggested that the reaction mechanism is different from that proposed by Verma et al The reaction was, therefore, reinvestigated in detail in an effort to put forward rate laws consistent with the experimental data, with a view to shedding more light on the mechanism of oxidation of amino acids by this oxidant as part of a series of investigations on amino acids carried out in our laboratory (3,4).…”