Mechanism of the oxidation of organic sulphides by permanganate ion

The kinetics of the oxidation of number of aryl methyl, alkyl phenyl, dialkyl and diphenyl sulphides by permanganate ion to yield the sulphoxides, have been studied. The reaction is first order with respect to the sulphide and permanganate and is independent of hydrogen ion concentration. The reaction exhibited negative polar reaction constants and a small degree of steric hindrance. The lack of solvent isotope effect and the observed solvent effect ( m = 0.39 for McSPh) are explained by an electrophilic attack of permanganate-oxygen on the sulphide yielding a polar transition state. A moderate anchimeric assistance was observed in the oxidation ofo-C00Me ando-C00H substituted methyl phenyl sulphide. A mechanism involving a one-step electrophilic oxygen transfer from permanganate ion to the sulphide and a polar product-like transition state, has been proposed.     

Kinetics and mechanism of the oxidation of acetylacetone by permanganate ion

The kinetics and mechanism of permanganate ion oxidation of acetylacetone (Acac) was studied in acidic and alkaline media. The rate constants for keto, enol, and enolate anions were determined and discussed. Delocalization of the π‐electrons of the double bond by conjugation results in a slower oxidation rate of enol than can be usually observed for unsaturated compounds. In the case of the keto form, the acid‐catalyzed nucleophilic attack of permanganate ion occurs on the carbonyl‐C atom. For enolate anion a mechanism with basis‐catalyzed electron abstraction is suggested. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 38: 444–450, 2006     

Kinetics of oxidation of hypophosphite ion by platinum(IV) in an alkaline medium

Summary The kinetics of the oxidation of hypophosphite ion by platinum(IV) have been studied spectrophotometrically in alkaline medium at different temperatures. The rate increases as the pH increases and the empirical rate law applicable to the reaction is given by:-d[Pt^IV]/dt = k₃[Pt^IV][H₂PO^2–][OH^–]The rate constant is 2.17×10^–3 (l² mo^–2s^–1) at 40.5°. The energy and entropy of activation for the reaction are 104.2 kJ mol^–1 and 28.5 JK^–1mol^–1 respectively.     

Kinetics of oxidation of hypophosphite ion by Au(III) in hydrochloric acid medium

Hypophosphite ion is oxidised by Au(III) in aqueous hydrochloric acid to give phosphorus acid and Au(I). The kinetics of the reaction has been studied spectrophotometrically in the UV region at different temperatures. The oxidation of hypophosphorous acid is first order with respect to both Au(III) and substrate. Hydrogen ion has no effect on the rate in acid media (0.15–1.0)M. The energy and entropy of activations are 128 ± 3.0kJ mol^?1 and 135.8 ± 6.5 JK^?1 mol^?1 respectively. The results are interpreted in terms of the probable formation of intermediate Au(lI).     

Kinetics and mechanism of oxidation of some simple reducing sugars by permanganate ion in alkaline medium

The kinetics of oxidation of glucose, galactose, fructose, maltose and sucrose by alkaline permanganate anion has been studied. The reactions studied spectrophotometrically over a wide range of experimental conditions show that the rate of the reactions is enhanced by increase in pH, ionic strength, and temperature as well as the reactant concentrations. The mechanism has been proposed to proceed via the formation of enediol intermediate complexes and the order of reactivities of the sugars is fructose > glucose ≈ galactose > maltose > sucrose. The activation parameters were evaluated and lend further support to the proposed mechanism.     

Lewis acid-activated oxidation of alcohols by permanganate

The oxidation of alcohols by KMnO(4) is greatly accelerated by various Lewis acids. Notably the rate is increased by 4 orders of magnitude in the presence of Ca(2+). The mechanisms of the oxidation of CH(3)OH and PhCH(OH)CH(3) by MnO(4)(-) and BF(3)·MnO(4)(-) have also been studied computationally by the DFT method.     

Oxidation with permanganate in presence of fluoride: Determination of hypophosphite

A rapid method is described for the determination of hypophosphite by oxidation with permanganate in acid medium in the presence of fluoride to prevent formation of insoluble oxides of manganese. The optimum conditions for visual and potentiometric end-point detection are given. Hypophosphite is oxidized to H(2)PO(-)(3). Under optimum conditions the titrations are fast and exhibit a reasonable potential change at the end-point. The method demonstrates the feasibility of determining amounts of H(2)PO(-)(2) corresponding to 0.08-7 mg of phosphorus.     

Study of the base-catalysed oxidation of the anti-bacterial and anti-protozoal agent metronidazole by permanganate ion in alkaline medium

The mechanism of dismutation of MnO₄ ^2? via the complex [MTZ–MnO₄·OH]^2?, formed during the oxidation of metronidazole (MTZ), has been investigated spectrophotometrically at different temperatures. The stoichiometry of the reaction is 1:1, i.e. 1 mol MTZ reacts with 1 mol Mn(VII).The reaction is first order in permanganate, less than first order in [MTZ] and [alkali]. The effects of added products and the dielectric constant and ionic strength of the reaction medium were investigated. The main products were identified by spot test and FT-IR. A mechanism involving a free radical has been proposed. In the equilibrium step MTZ binds to the MnO₄ ^? species to form a complex (C). Investigation of the reaction at different temperatures enabled determination of the activation data for the slow step of proposed mechanism. The proposed mechanism and the derived rate laws are consistent with the observed kinetics.     

Mechanism and kinetics of hydrogen oxidation on silver

The kinetic study of the stationary oxidation of hydrogen on silver was carried out. The dependences of the reaction rate on the ratios of hydrogen and oxygen in the reaction mixture under a constant total pressure of 1000 Pa were obtained at 423, 448, and 473 K. The reaction seems to proceed via the intermediate formation of surface hydroxyls. A kinetic equation of the reaction that satisfactorily described the experimental data was derived.     

Kinetics and mechanism of the oxidation of alkyl and aryl methyl ketones by permanganate ion in aqueous ethanoic acid

The kinetics of electron-transfer reactions between permanganate ion and ethyl and aryl methyl ketones have been studied in aqueous MeCO2H acid medium in the presence of HClO4 at different temperatures. For ethyl methyl ketone and XC6H4COMe (X = p-Cl, p-Br or p-NO2) the reaction obeys the rate law –d[MnO4–]/dt = (kKe[H+][MnO4–][RCO Me])/(1 + Ke[H+][RCOMe]).But the oxidations of XC6H4COMe (X = p-Me and p-OMe)follow the rate equation –d[MnO4–]/dt = k3[H+][MnO4–][RCOMe]. The reaction involves a fast pre-equilibrium with intermediate formation of a permanganate ester before the two-electron transfer, rate-determining, step. A number of thermodynamic parameters have been evaluated.     

Kinetics and mechanisms of the oxidation by permanganate of L-Phenylalanine

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.     

Salt effect in the oxidation of iodide by permanganate

The rate of the reaction between permanganate and iodide ions had been measured in several concentrated salt solutions. There is a salt effect, which is dependent on the hydration heat of the salt present in the reaction medium.

---

. , .

     

Vibrational spectra of hypophosphite ion and its deuterated species

The infrared and Raman spectra of the H₂PO₂^?, HDPO₂^? and D₂PO₂^? ions have been measured in aqueous solutions. The assignment of bands to the fundamental vibrations proposed is based on experimental tests, band polarisation measurements, application of all known isotopic rules and the construction and analysis of all the physically admissible assignments. The thermodynamic functions of the studied ions are calculated in the rigid rotator and harmonic vibrator approximation.