Kinetics of oxidation of sulphite by hexachloroplatinate(IV) in acidic solution

Summary The kinetics of the oxidation of sulphite by hexachloroplatinate(IV) has been studied over wide range of experimental conditions. The reaction is first-order in substrate and in platinum(IV). The rate decreases with the increase in acidity. The effect of salt and of changing dielectric constants on the reaction rate have been studied. Values of H and S have been calculated and are 26.3 kJ mol^–1 and –35.9 JK^–1 mol^–1, respectively. On the basis of experimental evidence, a two-electron reduction mechanism is proposed.     

Kinetics of the oxidation of octacyanomolybdate(IV) by periodate in aqueous acid

Summary The kinetics of oxidation of [Mo(CN)₈]^4– by IO ₄ ^– in aqueous acid is described by the equation: d[{Mo(CN)₈}^3–]/ dt=2k₃[{Mo(CN)₈}^4–][IO ₄ ^– ][H⁺]. Unlike IO ₄ ^– oxidations of [Fe(CN)₆]^4– and [W(CN)₈]^4–, no [H⁺] independent term exists in the [Mo(CN)₈]^4– reaction, which indicates that, in neutral and alkaline solutions, oxidation of [Mo(CN)₈]^4– is thermodynamically unfavourable. An inner-sphere mechanism, consistent with the rate law, is proposed. This conclusion is based, in the absence of direct evidence, on the observed behaviour of IO ₄ ^– as an inner-sphere oxidant.     

Kinetics and mechanism of sulphurous acid oxidation by hexachloroiridate(IV) in hydrochloric acid

Summary The reaction between sulphurous acid and hexachloroiridate(IV) appears to take place through the formation of an intermediate complex followed by decomposition to give oxidation products. The rate is retarded as the hydrogen ion concentration increases. Thermodynamic parameters associated with the equilibrium step as well as with the slowest step have been calculated. The probable mechanism of the reaction is discussed.     

Kinetics of the oxidation of oxalic acid by cerium(IV) sulfate in dilute sulfuric acid

The kinetics of the oxidation of oxalic acid by cerium(IV) in sulfuric acid medium has been studied voltammetrically. The specific reaction rate is 132±4.0 M^–1s^–1 at 25.0 °C. The energy of activation is 62.6±3.0 kJ mol^–1. The entropy of activation is –2.7 J mol^–1K^–1. The specific reaction rate is influenced by complexation and also by ionic strength (). The most likely mechanism has been suggested.

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(IV) . 132±4,0 M^–1c^–1 25,0 °C. 62,6±3,0 ·M^–1. –2,7 ·K^–1M^–1. , (). .

     

Kinetics of the methylene blue oxidation by cerium(IV) in sulphuric acid solutions

The oxidation of methylene blue (MB⁺) by cerium(IV) was studied in 0.1–5 M H₂SO₄. The reaction proceeds via MB radical (MB^2+•) formed by one electron transfer to the oxidant. The radical is observed spectrophotometrically by a very intense absorbance at λ_max = 526 nm and by the e.p.r signal at g = 2.000. The kinetics of the fast radical formation are two orders of magnitude slower than its decomposition, which were examined using a stopped-flow method at 298 K under pseudo-first order conditions. The rate laws for the both steps were determined and a likely mechanism reported.     

Kinetics of oxidation of water by Mn(IV) sulfate in acid media

Kinetics of the Mn(IV)Mn(III) transition in the oxidation of watet to O₂ was investigated at 60–100°C in 6–15 M H₂SO₄. The reaction is approximately 2-nd order in Mn(IV) concentration in the process of oxidation and 1-st order in initial Mn(IV) concentration. The kinetics is interpreted by the existence of dimeric forms Mn(IV)·Mn(IV), Mn(IV)·Mn(III) and Mn(III)·Mn(III). The suggested mechanism includes O₂ formation directly in the coordination sphere of the Mn(IV)·Mn(IV) dimer in a polyelectronic process.

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Mn (IV)»Mn (III) O₂ 60–100°C 6–15 M H₂SO₄. Mn (IV) I- Mn (IV). [Mn (IV)]₂; [Mn(III)]₂ Mn(IV)·Mn (III). , [Mn (IV)]₂

     

Cerium (IV) oxidation rate of p-chloromandelic acid in perchlorate and sulfate media

The rate of the cerium (IV) oxidation of p-chloromandelic acid has been studied in perchlorate media at an ionic strength of 1.50 mol/dm³ by the stopped-flow technique and in H₂SO₄? MHSO₄ (M⁺ = Li⁺, Na⁺, K⁺) and H₂SO₄? MClO₄ (M⁺ = H⁺, Li⁺, Na⁺) mixtures at constant total electrolyte concentrations of 1.00 and 2.00 mol/dm³ using the conventional spectrophotometric method. In perchlorate media the kinetic data indicate the formation of two intermediate complexes between cerium (IV) and the organic substrate, but only one is significantly involved in the intramolecular electron-transfer process. The oxidation rate is markedly lower in sulfate media, where two reaction paths have been found to contribute to the overall redox reaction. The univalent cations examined exhibit negative specific effects upon the overall oxidation rate increasing in the order H⁺ < Li⁺ < Na⁺ < K⁺. Activation parameters have been also estimated.     

Kinetics and mechanism of oxidation of malonic acid by chromium(VI) in aqueous perchlorate medium

The kinetics of oxidation of malonic acid, studied in aqueous acid perchlorate, conform to the rate law

Kinetics and mechanism of oxidation of 1,4-butanediol by chromium(VI) in acid perchlorate medium

Summary The kinetics of oxidation of 1,4-butanediol by chromium(VI) was studied in acid perchlorate medium and the oxidation product of the diol was identified as 4-hydroxybutanal. The kinetic rate law observed accounted for the complex dependence of the hydrogen ion k=(k₂K₁[H+]+k₃K₁K₂[H+]²)/(1+K₁[H]+) where k is the observed second-order rate constant.     

Kinetics and mechanism of electron transfer reactions in aqueous solutions: Silver(I) catalyzed oxidation of aspartic acid by cerium (IV) in acid perchlorate medium

Silver(I) catalyzed oxidation of aspartic acid by cerium(IV) was studied in acid perchlorate medium. The stoichiometry of the reaction is represented by the eq. (i) Dimeric cerium(IV) species has been indicated and employed in calculations of monomeric cerium(IV) species concentrations. The reaction is second-order and uncatalyzed reaction also simultaneously occurs along with the silver(I) catalyzed reaction conforming to the rate law (ii) where k is an observed second-order rate constant. A probable reaction mechanism is suggested. © 1995 John Wiley & Sons, Inc.     

Kinetics of the oxidation of U (IV) by hydrogen peroxide in sulfuric acid medium

The kinetics of the reaction have been investigated in H₂SO₄ medium under different conditions. The observed bimolecular rate constant k_obs, has been found to depend on [H⁺]^?0.55 and to increase with the initial concentration ratio of the reactants R₀ = [H₂O₂]₀/[U (IV)]₀ above 0.49. The activation energy of the overall reaction has been determined as 13.79 and 14.3 kcal/mol at R₀ = 1 and 0.35, respectively. Consistent with experimental data, a detailed reaction mechanism has been proposed where the hydrolytic reaction (4) followed by the rate-controlling reaction (10) and subsequent fast reactions of U (V) and OH radicals are involved: A kinetic expression has been derived from which a graphical evaluation of (kK₄)^?1 and k^?1 has been made at R₀ = 1 as (12.30 ± 0.09) × 10^?3 M min, (6.23 ± 2.19) × 10^?4 M min; and at R₀ = 0.35 as (12.63 ± 2.13) × 10^?3 M min, (8.32 ± 6.62) × 10^?4 M min, respectively. Indications of some participation of a chain reactionat R₀ = 1 have been obtained without affecting thesecond-order kinetics as observed.     

Kinetics and mechanism of oxidation of L-ascorbic acid by platinum(IV) in aqueous acid medium

The oxidation of l-ascorbic acid (H₂A) by platinum(IV) in aqueous acid medium exhibits overall second-order kinetics, being first order with respect to each reactant. Increasing both hydrogen and chloride ion concentrations inhibits the rate. The stoichiometry involves reaction of one platinum(IV) ion with H₂A to give dehydroascorbic acid. A reaction mechanism consistent with all the experimental observations is proposed.     

Kinetics of oxidation of organic compounds by silver(II) in aqueous perchloric acid solution. IV. Aliphatic alcohols

The kinetics and mechanism of the silver(II) oxidation of methanol, ethanol, 1-propanol, 1-methyl- ethanol, 1-butanol, 2-methyl-1-propanol, 2-butanol, 2-methyl-2-propanol, D₄-methanol, and D₆-methanol have been investigated at 8.0 and 20.0°C in aqueous perchloric acid media (1.00 ≤ [HClO₄] ≤ 4.00M; μ = 4.0M). The kinetics were monitored by following the disappearance of Ag(II) with a spectrophotometric stopped-flow technique. The reactions are first order in each reactant and involve both Ag²⁺ and AgOH⁺ species. No kinetic or spectroscopic evidence for complex formation between reactants was obtained. The results are discussed with reference to electron density on the ? OH or αC-H substrate sites and to the isotopic hydrogen/deuterium rate quotients found for methanol and ethanol.     

Kinetics and mechanism of oxidation of tellurium(IV) by cobalt(III) in perchloric acid

Summary The kinetics of oxidation of Te^IV by Co^III have been studied in aqueous HClO₄. A mechanism presuming [Co(OH₂)₅(OH)]²⁺ to be the reactive species has been proposed, which leads to the rate-equation shown. Rate=–d[Co^III]/dt=2kKK _h ² [Co^III] _t ² [Te^IV]/[H⁺]² K_b is the hydrolysis constant of Co^III, K is the formation constant of the complex between Co^III and Te^IV and k is the rate of decomposition of that complex. E_a and S are 95.0±2.1 kJ mol^–1 and 28.3±7.1 JK^–1 mol^–1, respectively.     

Kinetics of oxidation of manganese(II) by peroxomonosulfuric acid in aqueous acidic solution

Summary Oxidation of Mn _aq ²⁺ by HSO ₅ ^– in acetate buffer to manganese(IV) is autocatalytic, and obeys a rate expression of the general form -d[Mn^II]/dt = k₀[Mn^II] + k₁[Mn^II][MnO_x]. The first-order (k₀) and heterogenetic (k₁) rate constants show first-order dependences on [HSO ₅ ^– ] and on 1/[H⁺]. The reaction is catalyzed by the addition of the chelating ligand glycine; k₁ shows a first-order dependence on [glycine] at a fixed pH. This catalysis is ascribed to complexation, whereby the redox potential for Mn(gly) _n ^(2–n)+ is lower than that for Mn _aq ²⁺ , facilitating oxidation. The stoichiometry of the reaction is Mn²⁺: HSO ₅ ^– = 11, and the manganese(IV) oxide formed is of battery-active grade. Purity of the recovered product is not affected by the presence of high concentrations of natural sugars in the initial solution.