Kinetics and mechanism of oxidation of thallium(I) by 12-tungstocobaltate(III)in aqueous hydrochloric acid

The reaction between Tl^I and [Co^IIIW₁₂O₄₀]^5– proceeds in two one-electron steps, involving formation of unstable Tl^II in a slow first step followed by reaction with oxidant in a fast step. The reaction rate is unaffected by the [H⁺] as protonation equilibria are not involved with either reactant, whereas the accelerating effect of chloride ion is due to the formation of an active chloro-complex of the reductant, TlCl₃ ^2–. Increasing the ionic strength and decreasing the relative permittivity of the medium increases the rate of the reaction which is attributed to the formation of an outer sphere complex between the reactants. The activation parameters were also determined and the values support the proposed mechanism.     

Kinetics and mechanism of oxidation of arsenious acid by tetrachloroaurate(III) in hydrochloric acid medium

Kinetics of the oxidation of arsenious acid by tetrahcloroaurate(III) have been studied spectrophotometrically in hydrochloric acid medium. Initial complex formation between As(III) and Au(III) followed by the decomposition of the intermediate complex to give products of the reaction is suggested. The empirical rate law is

k and K are found to be 13.9 × 10^?4 s^?1 and 24.2 M^?1 respectively at 30°C and μ = 1.0 M. ΔH³ and ΔS³ for k are found to be 49.2 kJ mol^?1 and - 137.2 JK^?1 mol^?1 whereas ΔH and ΔS associated with K are - 6.75 kJ mol^?1 and 4.14 JK^?1 respectively.     

Kinetics and mechanism of the oxidation of hydrazinium ion by gold(III) in hydrochloric acid medium

Summary Kinetics of the oxidation of hydrazinium ion by gold(III) have been studied spectrophotometrically in hydrochloric acid medium. The reaction is first-order with respect to both gold(III) and hydrazinium ion. Hydrogen ion inhibits the oxidation. The mechanism of the reaction is discussed.     

Manganese(III) oxidation of L‐serine in aqueous sulfuric acid medium: Kinetics and mechanism

Kinetics and mechanism of oxidation of L‐serine by manganese(III) ions have been studied in aqueous sulfuric acid medium at 323 K. Manganese(III) sulfate was prepared by an electrolytic oxidation of manganous sulfate in aqueous sulfuric acid. The dependencies of the reaction rate are: an unusual one and a half‐order on [Mn(III)], first‐order on [ser], an inverse first‐order on [H⁺], and an inverse fractional‐order on [Mn(II)]. Effects of complexing agents and varying solvent composition were studied. Solvent isotope studies in D₂O medium were made. The dependence of the reaction rate on temperature was studied and activation parameters were computed from Arrhenius‐Eyring plots. A mechanism consistent with the observed kinetic data has been proposed and discussed. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 525–530, 1999     

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 aurate(I) by peroxydisulphate in aqueous hydrochloric acid

The reaction between Au(I), generated by reaction of thallium(I) with Au(III), and peroxydisulphate was studied in 5 mol dm^?3 hydrochloric acid. The reaction proceeds with the formation of an ion‐pair between peroxydisulphate and chloride ion as the Michealis–Menten plot was linear with intercept. The ion‐pair thus formed oxidizes AuCl₂^? in a slow two‐electron transfer step without any formation of free radicals. The ion‐pair formation constant and the rate constant for the slow step were determined as 113 ± 20 dm^?3 mol^?1 and 5.0 ± 1.0 × 10^?2 dm³ mol^?1 s^?1, respectively. The reaction was retarded by hydrogen ion, and formation of unreactive protonated form of the reductant, HAuCl₂, causes the rate inhibition. From the hydrogen ion dependence of the reaction rate, the protonation constant was calculated to be as 0.6 ± 0.1 dm³ mol^?1. The activation parameters were determined and the values support the proposed mechanism. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 589–594, 2002     

Kinetics and mechanism of oxidation of l‐ascorbic acid by peroxomonophosphate in aqueous acid medium

The kinetics of oxidation of l ‐ascorbic acid (H₂A) by peroxomonophosphate in acid aqueous medium has been studied. The stoichiometry of the reaction corresponds to the reaction as represented by the equation (1) where A is dehydroascorbic acid. The reaction is second order versus first order with respect to each reactant. The rate is retarded by hydrogen ion concentration. A plausible reaction mechanism has been suggested. The derived rate law (2) from such a mechanism accounts for all experimental observations: (2) Such pH dependence is somewhat different from that observed in the case of metal ion oxidants. © 2012 Wiley Periodicals, Inc. Int J Chem Kinet 45: 41–16, 2013     

Ruthenium(III)-catalyzed oxidation of thallium(i) by 12-tungstocobaltate(III) in hydrochloric acid medium

The reaction between thallium(I) and [Co^IIIW₁₂O₄₀]^5- in the presence of ruthenium(III) as catalyst proceeds viainitial outer-sphere oxidation of the catalyst to ruthenium(VI). The ruthenium(IV) thus generated will oxidize thallium(I) to an unstable thallium(II) which by reacting with oxidant gives the final product, thallium(III). The formation of ruthenium(II) by direct two-electron reduction of the catalyst by thallium(I) is thermodynamically less favorable. The reaction rate is unaffected by the [ H⁺ ], whereas it is catalyzed by chloride ion . The formation of reactive chlorocomplex,TlCl, in a prior equilibrium is the reason for the chloride ion catalysis. Increasing the relative permittivity of the medium increases the rate of the reaction, which is attributed to the formation of an outer-sphere complex between the catalyst and oxidant. This revised version was published online in June 2006 with corrections to the Cover Date.     

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.     

Chloride and iodide mediated oxidation of antimony(III) by cerium(IV) in aqueous sulphuric acid medium

The micro amounts of iodide (10⁻⁷) (mol dm⁻³) and chloride (10⁻²) (mol dm⁻³) mediated oxidation of antimony(III) by cerium(IV) in an aqueous sulphuric acid medium have been studied spectrophotometrically at 25 °C and μ = 3.10 mol dm⁻³. The stoichiometry is 1:2 in chloride and iodide mediated reactions. i.e. one mole of antimony(III) requires two moles of cerium(IV). In the case of chloride mediated reaction, the reaction was first order in cerium(IV) and halide concentrations, whereas in the case of iodide mediated reaction the order with respect to [cerium(IV)] was unity and with respect to iodide concentrations was more than unity (ca. 1.4). In both chloride and iodide mediated reactions the order with respect to antimony(III) concentrations was less than unity. Increase in sulphuric acid concentration increased the rate. The order with respect to H⁺ ion concentration was less than unity. Added products, cerium(III) and antimony(V) did not have any significant effect on the reaction rate. The active species of oxidant was understood to be , whereas that of reductant as SbCl₃ in the case of chloride and SbI²⁺ in case of iodide mediated reactions. The possible reaction mechanisms were proposed and the activation parameters were determined and discussed.     

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 and mechanism of oxidation of formic acid by bismuth(V) in aqueous phosphoric acid medium

The solution of bismuth(V) was prepared by digesting sodium bismuthate in aqueous phosphoric acid (3.0 mol dm⁻³), the resulting pink colour solution absorbs in the visible region at 530 nm (640 dm³ mol⁻¹ cm⁻¹). The stoichiometry of the oxidation of formic acid by bismuth(V) corresponds to the reaction as represented by the Eq. ( 1 ). (1) The observed kinetic rate law is given by the Eq. ( 2 ); (2) where Bi^V and [HCO₂H] are the gross analytical concentrations of bismuth(V) and formic acid respectively. A plausible reaction mechanism corresponding to the rate law (2) has been proposed. Also the pattern of reactivity of bismuth(V) in HCIOHF mixture and H₃PO₄ respectively has been compared. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 491–497, 2000     

Kinetics and mechanism of oxidation of 2‐mercaptosuccinic acid by bis(μ‐oxo)‐ manganese(III,IV)‐cyclam complex in aqueous medium: Influence of externally added copper(II)

Kinetic studies on the oxidation of 2‐mercaptosuccinic acid by dinuclear [Mn₂^III/IV(μ‐O)₂(cyclam)₂](ClO₄)₃] ( 1 ) (abbreviated as Mn^III–Mn^IV) (cyclam = 1,4,8,11‐tetraaza‐cyclotetradecane) have been carried out in aqueous medium in the pH range of 4.0–6.0, in the presence of acetate buffer at 30°C by UV–vis spectrophotometry. In the pH region, two species of complex 1 (Mn^III–Mn^IV and Mn^III–Mn^IVH, the later being μ‐O protonated form) were found to be kinetically significant. The first‐order dependence of the rate of the reactions on [Thiol] both in presence and absence of externally added copper(II) ions, first‐order dependence on [Cu²⁺] and a decrease of rate of the reactions with increase in pH have been rationalized by suitable sequence of reactions. Protonation of μ‐O bridge of 1 is evidenced by the perchloric acid catalyzed decomposition of 1 to mononuclear Mn(III) and Mn(IV) complex observed by UV–vis and EPR spectroscopy. The kinetic features have been rationalized considering Cu(RSH) as the reactive intermediate. EPR spectroscopy lends support for this. The formation of a hydrogen bonded outer‐sphere adduct between the reductant and the complex in the lower pH range prior to electron transfer reactions is most likely to occur. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 170–177 2004     

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 of oxidation of pyridoxine by anodically generated manganese(III) in aqueous acetic acid medium

Summary Manganese(III) acetate was prepared by the electrolytic oxidation of Mn(OAc)₂ in aqueous AcOH. The electro-generated manganese(III) species was characterised by spectroscopic and redox potential studies. The kinetics of oxidation of pyridoxine (PRX) by manganese(III) in aqueous AcOH were investigated and is first order with respect to [Mn^III]. The effects of varying [Mn^III], [PRX], added manganese(II), pH and added anions such as AcO⁻, F⁻, Cl⁻ and ClO _inf4 ^sup− and SO _inf4 ^sup2− were studied. The rate decreased slowly with increasing [H⁺] up to 0.2 mol dm⁻³ and increased steeply thereafter. The orders in [PRX] and [Mn^II] were unity and inverse fractional, respectively, in both low and high [H⁺] ranges. The dependence of reaction rate on temperature was studied and activation parameters were computed from Arrhenius and Eyring plots. A mechanism consistent with the observed results is proposed and discussed.     

Kinetics and mechanism of oxidation of xylitol and galactitol by hexacyanoferrate(III) ion in aqueous alkaline medium

Kinetics of oxidation of xylitol and galactitol by hexacyanoferrate(III) ion in aqueous alkaline medium is reported. The reaction rate is of first order with respect to hexacyanoferrate(III) in each substrate. The reaction is first order at lower concentrations of xylitol and galactitol and tends towards zero order as the concentration increases. Similarly first order kinetics was obtained with respect to hydroxide ion at lower concentrations and tends to lower order at higher concentration in the oxidation of xylitol; in the oxidation of galactitol the reaction is first order with respect to hydroxide ion even up to manyfold variation. The course of reaction has been considered to proceed through the formation of an activated complex between [K Fe(CN)₆]^2– and substrate anion which decomposes slowly into radical and [K Fe(CN)₆]^3–. A probable reaction mechanism is proposed.

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Kinetik und Mechanismus der Oxidation von Xylit und Galaktit mit Hexacyanoferrat(III) in wäßriger, alkalischer Lösung

Zusammenfassung Das Geschwindigkeitsgesetz der Titelreaktion ist in beiden Fällen erster Ordnung bezüglich Hexacyanoferrat(III). Die Oxidation ist erster Ordnung bei niedrigen Konzentrationen von Xylit und Galaktit und geht bei Erhöhung der Konzentration gegen null. In gleicher Weise wurde eine Kinetik erster Ordnung bezüglich Hydroxyl bei niedrigen Konzentrationen und eine erniedrigte Ordnung bei höheren Konzentrationen für die Oxidation von Xylit beobachtet; bei Galaktit bleibt die Oxidation auch bei höheren Hydroxyl-Konzentrationen erster Ordnung. Es wird angenommen, daß die Reaktion über einen aktivierten Komplex zwischen [KFe(CN)₆]^2– und dem Substrat-Anion verläuft; dieser Komplex zerfällt in [KFe(CN)₆]^3– und ein Substrat-Radikal. Ein möglicher Reaktionsmechanismus wird vorgeschlagen.

     

Kinetics and mechanism of dissociation of oxalatobis(phenanthroline)cobalt(III) ion in aqueous hydrochloric acid media

The kinetics of dissociation of oxalatobis(phenanthroline)cobalt(III) ion into cis-diaquobis(phenanthroline)cobalt(III) ion in aqueous HClKCl media have been studied. The rate is first-order with respect to acid concentration (1–2 M) with a specific rate constant, k_H = 6.2 × 10⁻⁴M⁻¹min⁻¹ at 75°C (μ, 2 M); ΔH^≠ and ΔS^≠ values are 22.1 kcal mole⁻¹ and −18.7 e.u., respectively. The magnitude of the ΔS^≠ value appears consistent with a dissociation mechanism involving reaction of the conjugate acid form of the complex (S_N 1CA mechanism).