Kinetics and mechanism of the oxidation ofL-α-amino-n-butyric acid in moderately concentrated sulfuric acid medium

Abstract

The reaction kinetics of L-α-amino-n-butyric acid oxidation by permanganate ion have been investigated in moderately strong acid medium using a spectrophotometric technique. In all cases studied an autocatalytic effect, due to Mn+2 ions formed as a reaction product, was observed. Both catalytic and noncatalytic processes were determined to be first order with respect to the permanganate ion and the amino acid. The overall rate equation for this process may be written as: [Formula: see text] where k′1 and k′2 are pseudo-order rate constants for the noncatalytic and catalytic reactions, respectively. The influence of some factors such as temperature and reactant concentration on the rate constants has been studied, and the activation parameters have been calculated. Reaction mechanisms satisfying observations for both catalytic and noncatalytic routes have been presented.Key words: L-α-amino-n-butyric acid, permanganate oxidation, concentrated acidic medium, autocatalysis, free radical intermediates.

Delayed autocatalytic behavior of Mn(II) ions at a critical ratio: The effect of structural isomerism on permanganic oxidation of L‐norleucine

“…Same trends for L-iso-leucine and L-tert-leucine similar to L-norleucine have been observed, so it could be concluded that Mn 2+ is the autocatalytic agent. But in contrast to our previous studies [15,16], for Mn 2+ to show "delayed autocatalytic characteristic," it should acquire a certain concentration, which we call "critical concentration." This critical concentration depends on the nature of amino acid used.…”

“…In our previous studies [15,16], we have reported the presence of an autocatalytic effect in which Mn 2+ is an autocatalytic agent. In the present investigation, we have examined oxidation of L-norleucine, L-leucine, L-iso-leucine, and L-tert-leucine in strong acid medium by permanganate.…”

“…Also positive δ c values indicate that increasing steric hindrance toward the ␣-carbon causes a decrease in the reaction rate in a noncatalytic pathway. Considering the mechanism mentioned in our previous study [16] for these reactions, radical release is an effective step in the determination of reaction rate. Since by increasing electron-donating character of carbon chain, radical production is eased, then the reaction rate is increased as expected.…”

“…Kinetic and mechanistic study of amino acid oxidation in strong acid medium by permanganate has re-ceived considerable attention since the 1970s [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16]. In most of these studies, the reaction has been considered as a process that follows a perfect secondorder kinetics at constant [H + ] and without any autocatalytic effect present.…”

Kinetic studies in the surfactant catalyzed oxidative deamination and decarboxylation of L-Valine by permanganate in sulphuric acid medium

“…Deamination and decarboxylation in the chromium(III)-catalysed oxidation of L-valine by alkaline permanganate and analysis of chromium(III) in microscopic amounts by a kinetic method was studied by Kulkarni and coworkers [10] .Kinetic and mechanistic studies of oxidation of glycine and valine by Nbromosuccinimide using chloro complex of Rh(III) in its nano-concentration range as homogeneous catalyst investigated by Singh et al [11] .Kinetics and mechanisms of the permanganate oxidation of L-valine in neutral aqueous solutions was studied by Perez-benito et al [12] . Bahrami [13] had investigated kinetics and mechanism of the oxidation of L-amino-n-butyric acid in moderately concentrated sulfuric acid medium.Studies in the kinetics of oxidation of some amino acids like glycine, alanine, phenylalanine, serine, threonine, aspartic and glutamic acid by KMnO 4 in a moderately concentrated H 2 SO 4 medium in the presence and absence of Ag + has been carried out by number of workers [14][15] . Literature survey reveals that permanganate ions are widely used as oxidizing agent in synthetic and analytical chemistry [16][17] .It has several advantages as an analytical reagent.It is strong and vividly coloured.In acidic medium it exists in different forms as HMnO 4 , HMnO 4 + , HMnO 3 , Mn 2 O 7 and one depending on the nature of the reductant [18] .Glycine being a simplest amino acids and mild reductant requires powerful oxidants for studying its kinetic behavior [19] due to this permanganate is assigned as oxidant in the present investigation.…”