Kinetics and mechanism of the oxidation of halotoluenes by acidic hexacyanoferrate(III)

The oxidation of halotoluenes by hexacyanoferrate(III) in aqueous acetic acid containing perchloric acid (0.5M) at 50°C gave the corresponding aldehyde as the major product, and a small amount of polymeric material. The order with respect to each of the reactants—substrate, oxidant, and acid—was found to be unity. Increasing proportions of acetic acid increased the rate of the reaction. The reaction was influenced by changes in temperature, and the activation parameters have been evaluated. The Hammett plot yielded a ρ⁺ value of ?1.8. A kinetic isotope effect k_H/k_D = 6.0 has been observed. The pathway for the conversion of the halotoluenes to the products has been mechanistically visualized as proceeding through the benzylic radical intermediate, formed in the rate-determining step of the reaction. The radical undergoes rapid conversion to the products.     

Kinetics and mechanism of oxidation of phenylhydrazine and P-bromophenylhydrazine by hexacyanoferrate(III) in acidic medium

Kietics of oxidation of phenylhydrazine and p-bromophenylhydrazine by hexacyanoferrate(III) in acidic medium have been studied. The reactions follow similar kinetics, being first order with respect to both hydrazine and exacyanoferrate(III) and inverse first order with respect to the hydrogen ion. Addition of hexacyanoferrate(II) has no retarding effect on the rate of oxidation. The effects of varying ionic strength, dielectric constant, and temperature on the reaction rates have been investigated. A plausible mechanism has been proposed to account for the experimental results. Benzene and bromobenzene have been identified as the oxidation products.     

Kinetics and mechanism of oxidation of quinol by alkaline hexacyanoferrate(III)

The reaction between quinol and alkaline hexacyanoferrate(III) at constant ionic strength gives p-benzoquinone. The rate of the reaction was first order in the concentrations of substrate, oxidant and alkali. The slow step of the reaction involves the formation of the p-benzosemiquinone radical, which was detected by esr spectroscopy as a five-line spectrum with peak intensity ratios of 14641.

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(III) -. , . - , , 14641.

     

Kinetics of the oxidation of hexacyanoferrate(III) with pyrolusite

It is established that the oxidation of potassium ferricyanide at pH 7–11 proceeds as a pseudo-second-order reaction with rate constants of 2.93, 4.19, 6.16, 8.66, and 9.22 L/(mol min) at 313, 323, 333, 343, and 353 K, respectively. The activation energy of the reaction is found to be 27.82 kJ/mol. The second order of the reaction, as along with the non-dependence of the rate constant on the liquid-phase volume: solidphase weight ratio, and on the rotation speed of the mixer, allow us to assume that the reaction proceeds in the kinetic region with a transition to the diffusion-kinetic mode at 353 K.     

Kinetics of the Ru(III) catalyzed oxidation of formaldehyde and acetaldehyde by alkaline hexacyanoferrate(III)

The kinetics of ruthenium(III) catalyzed oxidation of formaldehyde and acetaldehyde by alkaline hexacyanoferrate(III) has been studied spectrophotometrically. The rate of oxidation of formaldehyde is directly proportional to [Fe(CN) _3– ⁶ ] while that of acetaldehyde is proportional tok[Fe(CN) _3– ⁶ ]/{k +k[Fe(CN) _3– ⁶ ]}, wherek, k andk are rate constants. The order of reaction in acetylaldehyde is unity while that in formaldehyde falls from 1 to 0. The rate of reaction is proportional to [Ru(III)] _T in each case. A suitable mechanism is proposed and discussed.

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Die Kinetik der Ru(III)-katalysierten Oxidation von Formaldehyd und Acetaldehyd mittels alkalischem Hexacyanoferrat(III)

Zusammenfassung Die Untersuchung der Kinetik erfolgte spektrophotometrisch. Die Geschwindigkeitskonstante der Oxidation von Formaldehyd ist direkt proportional zu [Fe(CN) _3– ⁶ ], währenddessen die entsprechende Konstante für Acetaldehyd proportional zuk[Fe(CN) _3– ⁶ ]/{k +k[Fe(CN) _3– ⁶ ]} ist, wobeik,k undk Geschwindigkeitskonstanten sind. Die Reaktionsordnung für Acetaldehyd ist eine erste, die für Formaldehyd fällt von erster bis zu nullter Ordnung. Die Geschwindigkeitskonstante ist in jedem Fall proportional zu [Ru(III)] _T . Es wird ein passender Mechanismus vorgeschlagen.

     

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 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 ruthernium(III) catalyzed oxidation of propane-1,3-diol by alkaline hexacyanoferrate(III)

The kinetics of oxidation of propane-1,3-diol by alkaline hexacyanoferrate (III) catalyzed by ruthenium trichloride has been studied spectrophotometrically. A reaction mechanism involving the formation of an intermediate complex between the substrate and the catalyst is proposed. In the rate-determining step this complex is attacked by hexacyanoferate(III) forming a free radical which is further oxidized.     

Kinetics and mechanism of a trans-tetraazamacrocyclic chromium(III) complex oxidation by hexacyanoferrate(III) in strongly alkaline media

Oxidation of the trans-[Cr(cyca)(OH)₂]⁺ complex, where cyca = meso-5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane, by [Fe(CN)₆ ]^3- ion in strongly alkaline media, leading to [Cr^V O(cyca_ox )]³⁺ ion, has been studied using electronic and e.p.r. spectroscopy. The kinetics of the Cr^III → Cr^IV transformation have been studied using a large excess of the reductant and OH^- ion over the oxidant. The reaction is a second order process: first order in [Cr^III] and [Fe^III] at constant [OH^-]. The second order rate constant is higher than linearly dependent on the OH^- concentration. The mechanism of the reaction has been discussed. A relatively inert intermediate chromium(V) species was detected based on characteristic bands in the visible region and the e.p.r. signal at g_iso = 1.987 for the systems where an excess of oxidant was used. The hyperfine structure of the main e.p.r. signal is consistent with the d¹ -electron interactions with four equivalent nitrogen nuclei and [Cr^V = O(cyca_ox)]³⁺ formula, where cyca_ox = oxidized cyca, can be postulated for the intermediate Cr^V complex.     

Kinetics and mechanism of Os(VIII) catalysed oxidation of malate ion by alkaline hexacyanoferrate (III)

In the reaction between alkaline hexacyanoferrate(III) and malic acid catalysed by Os(VIII), the rate of hexacyanoferrate (III) disappearance was found to be proportional to the concentrations of malate ion, hydroxyl ion and Os(VIII), but independent of the concentration of hexacyanoferrate(III). The reaction was studied at different temperatures, various thermodynamic parameters ΔE, pZ, ΔS* etc were evaluated.     

Kinetics and mechanism of osmium(VIII)-catalyzed oxidation of 1,4-thioxane by alkaline hexacyanoferrate(III)

The kinetics of oxidation of 1,4-thioxane (1,4-oxathiane) by alkaline K₃Fe(CN)₆ have been studied in the presence of Os^VIII as catalyst. The reaction is first order in hexacyanoferrate(III) and Os^VIII. The order in thioxane and OH^– is zero. While added salts and ethanol have a negligible effect on the oxidation rate, K₄Fe(CN)₆ retards it. On the basis of kinetic evidence, a mechanism has been proposed.     

Rhodium(III) catalyzed oxidation of cyclic ketones by alkaline hexacyanoferrate(III)

The kinetics of the oxidation of 2-methyl cyclohexanone and cycloheptanone with Fe(CN)₆ ³⁻ catalyzed by RhCl₃ in alkaline medium was investigated at four temperatures. The rate follows direct proportionality with respect to lower concentrations of hexacyanoferrate(III) ion, but tends to become zero order at higher concentrations of the oxidant, while the reaction shows first-order kinetics with respect to hydroxide ion and cyclic ketone concentrations. The rate shows a peculiar nature with respect to RhCl₃ concentrations in that it increases with increase in catalyst at low catalyst concentrations but after reaching a maximum, further increase in concentration retards the rate. An increase in the ionic strength of the medium increases the rate, while increase in the Fe(CN)₆ ⁴⁻ concentration decreases the rate.     

Kinetics and mechanism of palladium (II) chloride catalyzed oxidation of allyl alcohol by potassium hexacyanoferrate (III)

A kinetic study of the oxidation of allyl alcohol by potassium hexacyanoferrate (III) in the presence of palladium (II) chloride is reported. The reaction was observed by measuring the disappearance of the potassium hexacyanoferrate (III) spectrophotometrically. The reaction is first order with respect to allyl alcohol and palladium (II) chloride, inverse second order with respect to [Cl^?], and zero order with respect to potassium hexacyanoferrate (III). The rate is found to increase linearly with hydroxyl ion concentration.     

Kinetics and mechanism of osmium(VIII)-catalyzed oxidation of hypophosphite by hexacyanoferrate(III) in aqueous alkali

The kinetics of osmium(VIII)-catalyzed oxidation of hypophosphite with hexacyanoferrate(III) in alkaline medium has been studied. The rate is independent of the concentration of the oxidant. The order with respect to hydroxide ion is variable. Rate law (1) conforms with the experimental observations.

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 a macrocyclic chromium(III) complex oxidation to chromium(IV) by hexacyanoferrate(III) in strongly alkaline media

Oxidation of the macrocyclic Cr(III) complex cis-[Cr(cycb)(OH)₂]⁺, where cycb=rac-5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane, by an excess of the hexacyanoferrate(III) in basic solution, slowly produces Cr(V) species. These species, detected using e.p.r. spectroscopy, are stable under ambient conditions for many hours, and the hyperfine structure of the e.p.r. spectrum is consistent with the interaction of the d-electron with four equivalent nitrogen nuclei. Electro-spray ionization mass spectrometry suggests a concomitant oxidation of the macrocyclic ligand, in which double bonds and double bonded oxygen atoms have been introduced. By comparison basic chromate(III) solutions are oxidized rapidly to chromate(VI) by hexacyanoferrate(III) without any detectable generation of stable Cr(V) intermediates.Kinetics of oxidation of the macrocyclic Cr(III) complex in alkaline solution has been studied under excess of the reductant. Rate determining formation of Cr(IV) by a second order process involving the Cr(III) and the Fe(III) reactants is seen. This reaction also involves a characteristic higher order than linear dependence on the hydroxide concentration. Reaction mechanisms for the processes, including oxidation of the coordinated macrocyclic ligand – under excess of the oxidant- are proposed.     

Kinetics and mechanisms of oxidation by metal ions. Part XIII. Osmium(VIII)-catalysed oxidation of cycloalkanols by alkaline hexacyanoferrate(III)

Summary The kinetics of OsO₄-catalysed oxidation of cyclopentanol, cyclohexanol and cyclooctanol by alkaline hexacyanoferrate(III) have been studied at low [OH^–] so that the equilibrium between alcohol and alkoxide ion is not unduly shifted towards the latter. The reaction shows a first-order dependence in [OH^–]. The order of the reaction with respect to cycloalcohol is fractional, indicating the formation of an intermediate complex with Os^VIII since the order with respect to hexacyanoferrate(III) ion is zero. The order with respect to Os^VIII may be expressed by the equation k_obs=a+b[Os^VIII]. The analysis of the rate data indicates a significant degree of complex formation between [OsO₃(OH)₃]^– and ROH. It was found that the bimolecular rate constant k for the redox reaction between complex and OH^–k₁, the forward rate constant for the formation of alkoxide ion. The activation parameters of these rate constants are reported.     

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.