Kinetics of tetraamminecopper(II)-catalysed oxidation of sulphur(IV) by peroxodisulphate in ammonia buffer

The kinetics of tetraamminecopper(II)-catalysed oxidation of SO^2– ₃ to SO^2– ₄ in ammonia buffers and in a nitrogen atmosphere obeys the rate law: –d[S^IV]/dt = k ₂[Cu^II][SO₃ ^2–][NH₃]^–1. There is spectrophotometric evidence for the formation of the intermediate complex [Cu(NH₃)₃(SO₃)] in a pre-equilibrium.     

Kinetics and mechanism of silver(I)-catalysed oxidation of 1,4-butanediol by peroxodiphosphate in acetate buffers

Summary The kinetics of silver(I)-catalysed oxidation of 1,4-butanediol by peroxodiphosphate (pdp) has been studied in acetate buffers. The diol oxidation product has been identified as 4-hydroxy-butanal by spectral analysis. The rate is independent of diol concentration and also hydrogen ion concentration in the pH region employed in the reaction. However, acetate ion radically retards the rate. A probable mechanism is proposed.     

Kinetics and mechanism of silver(I)-catalysed oxidation of malonic acid by peroxodiphosphate in acetate buffers

Summary The kinetics of the silver(I)-catalysed oxidation of malonic acid by peroxodiphosphate (pdp) was studied in acetate buffers. The rate law as represented by-d[pdp]/dt = {(k ₁ K _inf2 ^sup-1 [H⁺]² + k ₂[H⁺] + k ₃ K ₃)/ ([H⁺]²/K ₂ + [H⁺] + K ₃)}[pdp][Ag(I)] conforms to the proposed mechanism. The rate is independent of malonic acid concentrations. Acetate ions do not affect the rate; however, the rate decreases as the ionic strength increases. A probable portrait of reaction events is suggested. A comparative analysis of the reactivity pattern of malonic acid towards peroxodiphosphate and peroxodisulphate in presence of silver(I) has been made.     

Kinetics and mechanism of ruthenium(III)-catalysed oxidation of tellurium(IV) by alkaline diperiodatonickelate(IV)

The kinetics of Ru^III-catalysed oxidation of tellurium(IV) by alkaline diperiodatonickelate(IV) were studied spectrophotometrically using a rapid kinetic accessory. The reaction is a two stage process. In both the stages, the reaction is first-order with respect to [oxidant] and to [catalyst] with an apparent less than unit order, each in [substrate] and [alkali]. Periodate has a retarding effect on the reaction rate. A mechanism involving monoperiodatonickelate(IV) (MPN) as the reactive oxidant species is proposed. The data suggest that oxidation proceeds via formation of a complex between the active species of Ru^III and Te^IV, which then reacts with 1 mol of MPN in a slow step to yield the products. The reaction constants involved in the mechanism were evaluated. There is good agreement between the observed and calculated rate constants under varying experimental conditions for both the stages of reaction. The activation parameters for the slow step were calculated and discussed.     

Kinetics and mechanism of the ruthenium(III)-catalysed oxidation of aliphatic acids by peroxodiphosphate in acetate buffers

Summary The kinetics of oxidation of aliphatic acids (AAs), such as propionic acid, butyric acid, isobutyric acid and valeric acids, by peroxodiphosphate (PDP) using ruthenium(III) as catalyst in aqueous H₂SO₄ at constant ionic strength and different acidities were studied. The ruthenium(III)-catalysed oxidation is first order in [PDP] and fractional order in [AA]. The order with respect to [Ru^III] is fractional. An analysis of the rate dependence upon [H^–] suggests that H₃P₂O ₈ ^– is the active oxidizing species in the oxidation. A mechanism consistent with the rate law is proposed.     

Kinetics and mechanism of the ferroxime(II)-catalysed biomimetic oxidation of 2-aminophenol by dioxygen. A functional phenoxazinone synthase model

[Fe(Hdmg)(2)(MeIm)(2)](1), referred to as ferroxime(II), is the precursor of a selective catalyst for the oxidative dehydrogenation of 2-aminophenol (Hap) to 2-amino-3H-phenoxazine-3-one (apx) by dioxygen under ambient conditions. The superoxoferroxime(III) species has been detected by ES-MS, and a 4-substituted 2-aminophenoxyl free radical by the ESR technique. The kinetics of the reaction was followed spectrophotometrically and by monitoring dioxygen uptake at constant pressure. According to the proposed mechanism, solvolysis of 1 is followed by O(2) binding to afford a superoxoferroxime, which abstracts an H-atom from Hap in the rate-determining step via an H-bonded intermediate, generating the free radical. This is supported by the observed primary deuterium kinetic isotope effect of 2.63. The system studied is a functional phenoxazinone synthase model.     

Kinetics and mechanism of the ruthenium(III)-catalysed oxidation of aminoalcohols by cerium(IV) in a sulphuric acid medium

Summary The kinetics of the ruthenium(III)-catalysed oxidation of primary (viz. 2-aminoethanol and 3-aminopropanol) secondary (diethanolamine) and tertiary aminoalcohols (triethanolamine) by cerium(IV) in a sulphuric acid medium have been studied spectrophotometrically. The reactions exhibit a zero-order rate-dependence with respect to the oxidant and first-order rate-dependence with respect to each of the substrate and catalyst. First order dependence of rate in sulphuric acid is found for primary aminoalcohols. A suitable mechanism, consistent with the observed kinetic data, is proposed.     

Kinetics and mechanism of rhodium(III)-catalysed oxidation of 1,2-glycols by acid bromate

Summary Rh^III-catalysed oxidation of 1,2-glycols by acid bromate was studied in the presence of Hg(OAc)₂ at 40°C. The order is zero with respect to [BrO ₃ ^– ] and unity in [Rh^III] and in [glycol]. The oxidation rate is unaffected by variation in [H⁺] and added salts. Stoichiometric studies indicate that one mole of bromate consumes three moles of glycol giving the corresponding carbonyl compounds. A suitable mechanism involving direct reaction between Rh^III and glycol to give product,via hydride ion abstraction by Rh^III, is proposed.     

Kinetics and mechanism of the Co(II)-assisted oxidation of thioureas by dioxygen

Catalytic oxidation of N,N'-dimethylthiourea and thiourea by dioxygen in water using a new cobalt(II) complex of octasulfophenyltetrapyrazinoporphyrazine was performed under mild conditions. The reaction is shown to include the formation of an intermediate anionic five-coordinate complex followed by an unusual two-electron oxidation to produce the corresponding urea and elemental sulfur (S8). Kinetic and thermodynamic parameters for the different reaction steps of the process were determined. Drastic differences in catalytic activity of cobalt and iron octasulfophenyltetrapyrazinoporphyrazines were observed.     

Kinetics of oxidation of certain pyrimidines by Ce(IV)

The kinetics of the oxidation of certain biologically important pyrimidine bases (Uracil, Thymine, and 6-Methyluracil) by Ce(IV) in aqueous H₂SO₄ has been investigated. A first-order dependence of rate each on [Ce(IV)], [pyrimidine], and an inverse first-order dependence on [H₂SO₄] has been observed. Rate and activation parameters for the oxidation of these pyrimidines have been computed. A suitable rate law and a mechanism consistent with the kinetic observations and product analysis have been proposed. © 1996 John Wiley & Sons, Inc.     

Kinetics of copper(II)‐catalyzed oxidation of S(IV) by atmospheric oxygen in ammonia buffered solutions

To understand the chemistry of Cu(II)–NH₃–S(IV)–O₂ system, the kinetics of the oxidation of sulfur(IV) catalyzed by amminecopper(II) complexes has been studied in the ammonia‐buffered solutions. Sulfur(IV) is oxidized to sulfate. The complexes, Cu(NH₃)²⁺, Cu(NH₃)₂²⁺, and Cu(NH₃)²⁺₃ appear to be equally reactive and Cu(NH₃)₄²⁺ appears to be unreactive. The kinetics obey the rate law: where α₁ and γ₁ are the rate constants for O₂‐dependent and O₂‐independent pathways, respectively, for Cu(NH₃)²⁺, Cu(NH₃)²⁺₂, and Cu(N H₃)₃²⁺ complexes, which appear to be equally reactive. The values of α₁ and γ₁ were found to be (1.32 ± 0.21) × 10⁶ L² mol^?2 s^?1 (1.74 ± 0.40) × 10⁹ L³ mol^?3 s^?1respectively at 30°C. The reaction rate is not influenced by the presence of ethanol—a free radical scavenger, so a nonradical mechanism has been proposed. The results of this study are useful in understanding the atmospheric chemistry of aqueous phase autoxidation of dissolved sulfur dioxide in copper(II)–ammonia–sulfur(IV)–oxygen system at high pH. © 2011 Wiley Peiodicals, Inc. Int J Chem Kinet 43: 379–392, 2011     

Kinetics and mechanism of the ruthenium(III)-catalysed oxidation of aminoalcohols by alkaline hexacyanoferrate(III)

Summary The kinetics of the ruthenium(III)-catalysed oxidation of aminoalcoholsviz. 2-aminoethanol and 3-aminopropanol by alkaline hexacyanoferrate(III) has been studied spectrophotometrically. The reactions are rapid initially, then follow a second order rate dependence with respect to each of the catalyst and the oxidant. The second order rate dependence with respect to ruthenium(III) was observed for the first time. The order in [Aminoalcohol] and [OH^–] is unity in each case. A suitable mechanism, consistent with the observed kinetic data is postulated.     

Kinetics and mechanism of silver(I) catalysed autoxidation of aqueous sulphur(IV) in acetate buffered medium

The kinetics of the silver(I) catalysed autoxidation of aqueous sulphur(IV) an acetate buffered medium obey the rate law: –d[S^IV]/dt = D[Ag^I][S^IV]²[H⁺]^–1/(B+C[S^IV]). The rate is independent of [O₂] but strongly inhibited by EtOH. A free radical mechanism is proposed.     

Kinetics and mechanisms of oxidation by metalions. Part XI(1). Kinetics of the osmium(VIII)-catalysed oxidation of glycols by alkaline hexacyanoferrate(III)

Summary The kinetics of the Os^VIII-catalysed oxidation of glycols by alkaline hexacyanoferrate(III) ion exhibits zerothorder dependence in [Fe(CN) ₆ ^3– ] and first-order dependence in [OsO₄]. The order with respect to glycols is less than unity, whereas the rate dependence on [OH^–] is a combination of two rate constants; one independent of and the other first-order in [OH^–]. These observations are commensurate with a mechanism in which two complexes, [OsO₄(H₂O)G]^– and [OsO₄(OH)G]^2–, are formed either from [OsO₄(H₂O)(OH)]^– or [OsO₄(OH)₂]^2– and the glycol GH, or by [OsO₄(H₂O)₂] and [OsO₄(H₂O)(OH)]^– and the glycolate ion, G^–, which is in equilibrium with the glycol GH through the reaction between GH and OH^–. Hence there is an ambiguity about the true path for the formation of the two Os^VIII-glycol complexes. A reversal in the reactivity order of glycols in the two rate-determining steps, despite the common attack of OH^– ion on the two species of Os^VIII-complexes, indicates that the two complexes are structurally different because S changes from the negative (corresponding to k₁₁) to positive (related to k₂).     

Kinetics and mechanism of ruthenium(III)-catalysed oxidation of allyl alcohol by acid bromate-autocatalysis in catalysis

The kinetics of oxidation of CH₂=CHCH₂OH with KBrO₃ in the presence of Ru^III catalyst in aqueous acid medium has been studied under varying conditions. The active species of oxidant and catalyst were HBrO₃ and [Ru(H₂O)₆]³⁺ respectively. The autocatalysis exhibited by one of the products, i.e., Br^–, was attributed to the formation of a complex between the bromide ion and Ru^III. A composite scheme and rate law were proposed. Reaction constants involved in the mechanism have been evaluated.     

Kinetics and mechanism of oxidation of uric acid by hexacyanoferrate(III) in acetate buffers

The second order kinetics of uric acid oxidation by hexacyanoferrate(III) in acetate buffers were studied by estimating oxidant colorimetrically at 420 nm. Two moles of organic acid react with one mole of the oxidant and oxidation products are alloxan and urea. TMC 2661     

Kinetics and mechanism of the ruthenium(III)-catalysed oxidation of aminoalcohols by chloramine-T in perchloric acid

Summary The kinetics of the ruthenium(III) catalysed oxidation of 2-aminoethanol, 3-aminopropanol, diethanolamine and triethanolamine by chloramine-T in HClO₄ medium have been studied. The reactions exhibits first order rate dependence with respect to the oxidant and to the catalyst, and are zeroth order with respect to the substrate. The rate of oxidation is proportional to k[HClO₄]/{k+k'[HClO₄]} where k, k and k' are constants (a mixture of elementary rate constants and equilibrium constants). A suitable mechanism consistent with the observed kinetic data is proposed.     

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.