Kinetics and mechanism of oxidation of acetanilide by quinquevalent vanadium in acid medium

Summary The kinetics of the oxidation of acetanilide with vanadium(V) in sulphuric acid medium at constant ionic strength has been studied. The reaction is first order with oxidant. The order of reaction in acetanilide varies from one to zero. The reaction follows an acid catalyzed independent path, exhibiting square dependence in H⁺. A Bunnett plot indicates that the water acts as a nucleophile. The thermodynamic parameters have been computed. A probable reaction mechanism and rate law consistent with these data are given.

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Kinetik und Mechanismus der Oxydation von Acetanilid mit fünfwertigem Vanadium in saurem Medium

Zusammenfassung Es wurden kinetische Untersuchungen der Oxydation von Acetanilid mit Vanadium(V) in schwefelsaurem Medium bei konstanter Ionenstärke durchgeführt. Gegenüber dem Oxidans ist die Reaktion erster Ordnung, die Reaktionsordnung gegenüber Acetanilid variiert zwischen 1 und 0. Die Reaktion folgt einem von der Säurekatalyse unabhängigen Weg, wobei die Abhängigkeit von H⁺ quadratisch ist. Ein Bunnett-Plot zeigt, daß das Wasser als Nucleophil wirkt. Die thermodynamischen Parameter wurden berechnet. Ein möglicher Reaktionsmechanismus und ein Geschwindigkeitsnetz, das mit diesen Daten in Einklang ist, wird angegeben.

     

Coulometric titration with quinquevalent uranium determination of vanadium(v)

Variadium(V) has been determined by reduction with generated uranium(V) with an accuracy of about ± 0.3%. Amounts as small as 15 μg were successfully titrated. The suggested ph range is 1–2.5. Iron(III) is reduced simultaneuosly with vanadium(V).     

Mechanism of alcohol oxidation by dipicolinate vanadium(V): unexpected role of pyridine

Dipicolinate vanadium(V) alkoxide complexes (dipic)V(V)(O)(OR) (OR = isopropoxide (1), n-butanoxide (2), cyclobutanoxide (3), and α-tert-butylbenzylalkoxide (4)) react with pyridine to afford vanadium(IV) and 0.5 equiv of an aldehyde or ketone product. The role of pyridine in the reaction has been investigated. Both NMR and X-ray crystallography experiments indicate that pyridine coordinates to 1, which is in equilibrium with (dipic)V(V)(O)(O(i)Pr)(pyr) (1-Pyr). Kinetic studies of the alcohol oxidation suggest a pathway where the rate-limiting step is bimolecular and involves attack of pyridine on the C-H bond of the isopropoxide ligand of 1 or 1-Pyr. The oxidations of mechanistic probes cyclobutanol and α-tert-butylbenzylalcohol support a two-electron pathway proceeding through a vanadium(III) intermediate. The alcohol oxidation reaction is promoted by more basic pyridines and facilitated by electron-withdrawing substituents on the dipicolinate ligand. The involvement of base in the elementary alcohol oxidation step observed for the dipicolinate system is an unprecedented mechanism for vanadium-mediated alcohol oxidation and suggests new ways to tune reactivity and selectivity of vanadium catalysts.     

Kinetics and mechanism of oxidation ofL-arabinose by vanadium(V)

Vanadium(V) oxidation ofL-arabinose has been found to be first order with respect to oxidant and substrate concentrations. It has been found that the order with respect to [H⁺] changes from one in 2.5M–4.5M acid concentration range to two in 5.0M–6.5M acid concentration range. The oxidation rate has been found to increase with ionic strength and decrease with dielectric constant of the medium. Thermodynamic parameters E, S and G have been evaluated as 22.63±0.19 kcal/mol,–3.00±0.65 e. u. and 23.59±±0.05 kcal/mol respectively. The reaction has been found to be initiated by the formation of free radical in a slow rate determining step.

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Kinetik und mechanismus der oxidation von L-arabinose mit vanadium(V)

Zusammenfassung Die Vanadium(V)-Oxidation vonL-Arabinose verläuft bezüglich des Oxidationsmittels und Substrats erster Ordnung. Bezüglich der Änderung von [H⁺] zeigte sich für den Bereich 2,5M–4,5M eine Abhängigkeit erster, im Bereich 5,0M–6,5M eine von zweiter Ordnung. Die Oxidationsgeschwindigkeit steigt mit der Ionenstärke und fällt mit der Dielektrizitätskonstanten des Mediums. Es wurden die thermodynamischen Parameter E, S und G bestimmt: 22,63±0,19 kcal mol^–1. –3,00±0,65 e. u. und 23,59±±0,05 kcal mol^–1. Es wurde festgestellt, daß die Reaktion über die Bildung eines freien Radikals in einem langsamen, geschwindigkeitsbestimmenden Schritt initiiert wird.

     

Kinetics of EDTA-catalyzed oxidation of Indigo Carmine by vanadium(V)

The reaction is first order both in vanadium(V) and substrate and is markedly inhibited by H⁺ ions. Kinetic evidence for the formation of a 11 complex of vanadium(V) and EDTA is obtained. The stability constant of this complex and its thermodynamic parameters were evaluated. A suitable mechanism is proposed.

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(V), H⁺. 11 (V) . . .

     

Kinetics of oxidation of phenylacetic acid hydrazide by vanadium(V)

The title reaction was studied in aqueous perchloric acid medium in the presence of 15% acetic acid by volume. It was observed that the reaction proceeds via an intermediate 11 oxidant-substrate complex. The reaction is inhibited by H⁺ ions. A mechanism consistent with the experimental results is proposed.

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(V) - 15% . - - 11. , .

     

Photochemical oxidation of hydrocarbons by a vanadium(V) peroxo complex

The oxidation of alkanes and benzene by VO(O₂)L·2H₂O (L=2-picolinate) in acetonitrile is accelerated upon irradiation with visible and, especially, UV light. Cyclohexyl hydroperoxide, cyclohexanol, and cyclohexanone in approximately 2:1:1 ratio are formed from cyclohexane both in the dark and photochemical reactions. Benzene is oxidized to phenol.Istituto di Teoria e Struttura Elettronica dei Composti di Coordinazione, CNR, Area della Ricerca di Roma, via Salaria km 29.5, C. P. 10, 00016 Monterotondo Stazione, Rome, Italy. N. N. Semenov Institute of Chemical Physics, Russian Academy of Sciences, 117977 Moscow. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 8, pp. 1918–1921, August, 1992.     

Photo-induced oxidation of some organic carbonyl compounds by vanadium(V)

The oxidation of pyruvic acid, levulinic acid, acetaldehyde, isobutyraldehyde and acetylacetone by vanadium(V) in aqueous solution on illumination with visible light is described. Pyruvic acid undergoes oxidation much more rapidly than does levulinic acid ; both give acetic acid. Acetaldehyde is more rapidly oxidized than is isobutyraldehyde, the former giving formic acid, and the latter, formic acid and acetone. Acetylacetone is converted into acetic acid. The oxidations are rapid and quantitative and may be used for the estimation of these carbonyl compounds.     

Kinetics and mechanism of vanadium(IV) oxidation by tetrabutylammonium tribromide

The reaction between tetrabutylammonium tribromide(TBATB) and vanadium(IV) has been studied in 50% (v/v) acetic acid under second order conditions. The overall order of reaction is found to be two, unity in each reactant. The reaction involves two single-electron transfer steps generating bromine free radical in the first rate determining step. The test for the formation of free radicals in presence of added acrylonitrile was negative while added toluene increases the rate of the reaction considerably due to its conversion into benzyl bromide. The reaction is retarded by hydrogen ions as a result of protonation prior equilibria of the active reductant, vanadyl acetate. The oxidation of the vanadylsalen complex by TBATB proceeds more rapidly than that of vanadyl acetate but follows the similar kinetic behaviour. Considerable decrease in the entropy of activation of the reaction indicates formation of an ordered transition state between the two reactants and since the kinetic behaviour remains unaltered, even after the change in the ligand attached to the reductant, indicates an interaction between the reactants through the oxygen atom on the vanadyl ion.     

Kinetics of oxidation of vanadium(III) by hydroxylamine in acid medium

The kinetics of oxidation of vanadium(III) by hydroxylamine have been investigated at high acidities in the temperature range 25–30 °C. Rates decreased with increasing acidity of the medium. Both NH₂OH and NH₃OH⁺ are capable of oxidizing V(III) in parallel reactions, the order being unity each in oxidant and reductant.

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(III) 25–30 °C. . NH₂OH NH₃OH⁺ V(III) , , .

     

Aerobic oxidation reactions catalyzed by vanadium complexes of bis(phenolate) ligands

Vanadium(V) complexes of the tridentate bis(phenolate)pyridine ligand H(2)BPP (H(2)BPP = 2,6-(HOC(6)H(2)-2,4-(t)Bu(2))(2)NC(5)H(3)) and the bis(phenolate)amine ligand H(2)BPA (H(2)BPA = N,N-bis(2-hydroxy-4,5-dimethylbenzyl)propylamine) have been synthesized and characterized. The ability of the complexes to mediate the oxidative C-C bond cleavage of pinacol was tested. Reaction of the complex (BPP)V(V)(O)(O(i)Pr) (4) with pinacol afforded the monomeric vanadium(IV) product (BPP)V(IV)(O)(HO(i)Pr) (6) and acetone. Vanadium(IV) complex 6 was oxidized rapidly by air at room temperature in the presence of NEt(3), yielding the vanadium(V) cis-dioxo complex [(BPP)V(V)(O)(2)]HNEt(3). Complex (BPA)V(V)(O)(O(i)Pr) (5) reacted with pinacol at room temperature, to afford acetone and the vanadium(IV) dimer [(BPA)V(IV)(O)(HO(i)Pr)](2). Complexes 4 and 5 were evaluated as catalysts for the aerobic oxidation of 4-methoxybenzyl alcohol and arylglycerol β-aryl ether lignin model compounds. Although both 4 and 5 catalyzed the aerobic oxidation of 4-methoxybenzyl alcohol, complex 4 was found to be a more active and robust catalyst for oxidation of the lignin model compounds. The catalytic activities and selectivities of the bis(phenolate) complexes are compared to previously reported catalysts.     

Study of the kinetics of the oxidation of complexones by vanadium (V)

Conclusions The kinetics of the oxidation of ethylenediaminetetraacetic acid and diethylenetriaminepentaacetic acid by vanadium(V) was studied; the reaction is first order with respect to V(V) and the complexone. The reaction rate constants were determined, and the activation energies of the oxidation processes were calculated.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, pp. 1212–1215, June, 1973.     

Kinetics of oxidation of ethyldigol by vanadium(V) in aqueous acidic medium

The kinetics of oxidation of ethyldigol by vanadium(V) in aqueous acidic medium has been carried out. The reaction is first order with respect to vanadium(V) and the substrate and is acid catalysed.Hammett acidity function (H ₀) andBunnett hypothesis have been applied. The formation of free radicals during the course of the reaction has been indicated. A probable reaction mechanism is proposed.

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Die Kinetik der Oxidation von Ethyldigol mit Vanadium(V) in wäßrigem saurem Medium

Zusammenfassung Es wurde die Kinetik der Oxidation von Ethyldigol mittels Vanadium(V) in wäßriger saurer Lösung untersucht. Die Reaktion ist erster Ordnung bezüglich Vanadium(V) und Substrat und ist säurekatalysiert. Es wurden dieHammett-Aciditätsfunktion (H ₀) und dieBunnett-Hypothese angewandt. Die Bildung von freien Radikalen während der Reaktion konnte bestätigt werden. Es wird ein Reaktionsmechanismus vorgeschlagen.

     

Kinetics and mechanism of Os(VIII) catalyzed oxidation of dimethyl sulfoxide by vanadium(V)

The title reaction is first order each in vanadium(V) and Os(VIII) and fractional order with respect to DMSO. The rate is found to decrease with increasing concentrations of sulfuric, perchloric and acetic acid, whereas the rate increases with the increasing concentrations of sodium bisulfate and sodium perchlorate. Thermodynamic parameters like E_a, H, S and G were evaluated. A suitable mechanism consistent with the observed kinetics is proposed.     

钒(Ⅴ)催化溴酸钾氧化铍试剂Ⅲ的反应及其应用

基于在硫酸介质中钒(Ⅴ)催化溴酸钾氧化铍试剂Ⅲ的反应建立了测定痕量钒(Ⅴ)的新方法,研究了试剂浓度条件,讨论了反应机理,方法线性范围是0～0 50ng mL,检出限为7 0×10-12g mL,方法已用于矿泉水及蔬菜中钒的测定。     

Flow-injection chemiluminescent determination of vanadium(IV) and total vanadium by means of catalysis on the periodate oxidation of purpurogallin

A flow-injection chemiluminescent (CL) method is proposed for the successive determination of nanogram levels of vanadium(IV) and total vanadium. The method is based on the catalytic effect of vanadium(IV) on the oxidation of purpurogallin by periodate to produce light emission at 4 °C. The presence of hydrogen carbonate enhanced the light emission arising from the vanadium(IV)-catalyzed reaction. Since vanadium(V) did not catalyze the CL reaction of purpurogallin, vanadium(V) was determined after being reduced to vanadium(IV) by using an on-line silver-reducing column. Calibration curves for vanadium(IV) and (V) were linear in the range 0.1–10 ng ml⁻¹ with sampling rate of about 50 h⁻¹. The limit of detection for signal-to-noise ratio of 2 was 0.05 ng ml⁻¹ and the relative standard deviations were 1.4 and 1.6% for ten determinations of 2.0 ng ml⁻¹ vanadium(IV) and (V), respectively. Interferences from metal ions could be eliminated by the use of O,O′-bis(2-aminoethyl)ethyleneglycol- N,N,N′,N′-tetraacetic acid and diphosphate as masking agents. The proposed method was successfully applied to the determination of vanadium(IV) and total vanadium in fresh water samples.     

Kinetics and mechanism of palladium(II) chloride catalysed oxidation of unsaturated acids by vanadium(V)

Summary The kinetics of the palladium(II) catalysed oxidation of acrylic, methacrylic and crotonic acid by vanadium(V), in acid medium at constant ionic strength exhibit zeroth order dependence on vanadium(V) and first order dependence on palladium(II) and the unsaturated acid. Complex formation between the palladium(II) species and the unsaturated acid, with possible exchange of chloride ion and hydrogen ion in two successive steps, was invoked. The reaction rate is determined by a rearrangement leading to elimination of chloride ion. A plausible mechanism is proposed.     

Flow injection analysis for oxidation state speciation of vanadium(IV) and vanadium(V) in natural water.

A sensitive and simultaneous spectrophotometric flow injection method for the determination of vanadium(IV) and vanadium(V) is proposed. The method is based on the effect of ligands such as 2,4,6-tris(2-pyridyl)-1,3,5-triazine (TPTZ) and diphosphate on the conditional redox potential of iron(III)/iron(II) system. A four-channel flow system is assembled. In this flow system, diluted hydrochloric acid (1.0 x 10(-2) mol dm(-3)) as a carrier for standard/sample, acetate buffer (pH 5.5) as a carrier for diphosphate solution, an equimolar mixed solution of iron(III) and iron(II) and a TPTZ solution are delivered, so that the baseline absorbance can be established by forming a constant amount of iron(II)-TPTZ complex (lambda(max) = 593 nm). Vanadium(IV) and/or vanadium(V) (400 microL) and diphosphate (200 microL) solutions are simultaneously introduced into the flow system; in this system the diphosphate solution passes through a delay coil. The potential of the iron(III)/iron(II) system increases in the presence of TPTZ, and therefore vanadium(IV) is easily oxidized by iron(III) to vanadium(V) to produce an iron(II)-TPTZ complex (a positive peak for vanadium(IV) appears). On the other hand, the potential of the redox system decreases in the presence of diphosphate, so that vanadium(V) can be easily reduced by iron(II) to vanadium(IV). In this case, the amount of iron(II) decreases according to the amount of vanadium(V). As a result, the produced iron(II)-TPTZ complex decreases (a negative peak for vanadium(V) appears). In this manner, two peaks for vanadium(IV) and vanadium(V) can be alternately obtained. The limits of detection (S/N = 3) are 1.98 x 10(-7) and 2.97 x 10(-7) mol dm(-3) for vanadium(IV) and vanadium(V), respectively. The method is applied to the simultaneous determination of vanadium(IV) and vanadium(V) in commercial bottled mineral water samples.     

Mechanism of heterogeneous catalytic oxidation of acetone vapor on vanadium pentoxide

We have used an extensive set of kinetic data to consider the probable reaction mechanism for the oxidation of acetone on vanadium pentoxide at 433–473 K. It is concluded that a significant part is played by the stage of the reoxidation of the catalyst surface, coupled with the transfer of oxygen during the formation of the reaction products. Computer calculations have been used to determine the best values of the rate constants of the separate stages of the proposed mechanism.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 26, No. 1, pp. 115–120, January–February, 1990.