The kinetics of permanganate oxidation of L-phenylalanine in acid medium at a constant ionic strength has been investigated spectrophotometrically. An autocatalytic reaction was observed being autocatalyzed by a soluble form of Mn(1V).The reaction appears to involve a parallel consecutive reaction process in which Mn (1V)
The oxidation of three α-amino acids by permanganate under neutral conditions has been studied at various temperatures. The use of Exner's statistical method shows no existence of an isokinetic relation in the heterogeneous process but for the homogeneous process such a relation has been found. Moreover, the existence of linear free energy relations was confirmed for the homogeneous process.
The oxidation of glycine by permanganate ions was studied in a buffered solution at pH 2.2. An autocatalytic reaction was observed, autocatalyzed by a soluble form of Mn(IV). Autocatalytic S-shaped kinetic curves were obtained by the spectrophotometric method and characterized by the time ti vs concentration in the inflection point.
The oxidation of L-Phenylalanine by permanganate ion in aqueous phosphate buffers is autocatalized by the inorganic reaction product, which is stabilized in solution by adsorption of phosphate ions on its surface. This product is a soluble form of colloidal manganese dioxide. The rate of the noncatalytic reaction pathway is first-order in both the oxidizing and reducing agent. It is not affected by potassium chloride addition to the solution, but by phosphate addition. The rate increases with the pH of the medium. The autocatalytic pathway is first-order in both permanganate ion and colloidal manganese dioxide, (the permanganate ion according to the Langmuir isotherm). The autocatalytic rate increases with reductant concentration (follows the Langmuir adsorption isotherm). It is not affected by potassium chloride addition to the solution, whereas an increase in the phosphate concentration results in an increase in the rate with the same pH of the medium. Mechanisms consistent with the experimental data are proposed.
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The kinetics of L-alanine oxidation by permanganate ion in buffer solutions at pH 2.2 have been studied. Both spectrophotometric and kinetic evidence is provided for the existence of an intermediate Mn(IV) species of colloidal nature. An autocatalytic course of the oxidation is discussed.
M A R~A PIEDAD ALVAREZ-MACHO and M A R~A ISABEL MONTEQUI-MARTIN. Can. J. Chern. 68,29 (1990). The oxidation of lactlc acid by chromic acid was studied at high concentrations of HCIO?, HN03, and H2S04 It was observed that the reaction rate depends not only on the acidity of the medium, but also on the nature of the mineral acid. The use of the Bunnett and Bunnett-Olsen criteria and the excess acidity concept allows us to propose a reaction mechanism of the A-2 type, the rate-determining step being a bimolecular process in whlch water participates as a nucleophile. The enthalpy and entropy of activation were determined; the decrease of the magnitude of these parameters when the acidity of the medium was increased I suggests the existence of a compensation effect.
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