Kinetics and mechanism of the oxidation of some organic sulfides by morpholinium chlorochromate

The oxidation of organic sulfides by morpholinium chlorochromate (MCC) resulted in the formation of the corresponding sulfoxides. The reaction is first order with respect to both MCC and the sulfide. The reaction is catalyzed by toluene‐p‐sulfonic acid (TsOH). The oxidation was studied in 19 different organic solvents. An analysis of the solvent effect by Swain's equation showed that both the cation‐ and anion‐solvating powers of the solvents play important roles. The correlation analyses of the rate of oxidation of 34 sulfides were performed in terms of various single and multiparametric equations. For the aryl methyl sulfides, the best correlation is obtained with Charton's localized‐delocalized‐resonance and localized‐delocalized‐resonance‐steric equations. The oxidation of alkyl phenyl sulfides exhibited a very good correlation in terms of the Pavelich–Taft equation. The polar reaction constants are negative, indicating an electron‐deficient sulfur center in the rate‐determining step. A mechanism involving formation of a sulfonium cation intermediate in the slow step has been proposed. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 41: 65–72, 2009     

Kinetics of oxidation of benzyl alcohol by sodium N-chloro-p-toluenesulfonamide

The kinetics of oxidation of benzyl alcohol and substituted benzyl alcohols by sodium N-chloro-p-toluenesulfonamide (chloramine-T, CAT) in HClO₄ (0.1–1 mol/dm³) containing Cl^? ions, over the temperature range of 30–50°C have been studied. The reaction is of first order each with respect to alcohol and oxidant. The fractional order dependence of the rate on the concentrations of H⁺ and Cl^? suggests a complex formation between RNCl^? and HCl. In higher acidic chloride solution the rate of reaction is proportional to the concentrations of both H⁺ and Cl^7hyphen;. The observed solvent isotope effect (k/k) is 1.43 at 30°C. The reaction constant (p = ?1.66) and thermodynamic parameters are evaluated. Rate expressions and probable mechanisms for the observed kinetics have been suggested.     

Kinetics and mechanism of the oxidation of d-mannose with pyridinium chlorochromate

The kinetics of oxidation of D-mannose with pyridinium chlorochromate, C₅H₅NHCrO₃Cl, was investigated in aqueous perchloric acid medium. The ionic strength of the medium was maintained constant by adding sodium perchlorate solution. The oxidation process exhibits unit dependence in each of the reactants, namely D-mannose and pyridinium chlorochromate. The reaction is acid catalyzed. A 32 stoichiometry is observed in the oxidation and the reaction did not induce polymerization of acrylonitrile. Activation parameters have been computed by measuring the rates at different temperatures. A reaction mechanism consistent with the experimental observation is proposed.     

Kinetics and mechanism of oxidation of substituted benzaldehydes by 4-(dimethylamino)pyridinium chlorochromate

Kinetics of oxidation of substituted benzaldehydes by 4-(dimethylamino)pyridinium chlorochromate (DMAPCC) in protic solvent system has been studied at 303 K. The product of oxidation has been identified as benzoic acid. A unit order dependence of the reaction with respect [DMAPCC] and [benzaldehyde] has been observed. The reaction has been found to be catalysed by H⁺ ions. Decrease in the dielectric constant of the medium decreases the rate. To study the effect of structure reactivity relationships some para-substituted benzaldehydes were subjected to oxidation kinetics by DMAPCC at four different temperatures and thermodynamic parameters were calculated. The isokinetic plot and Exner plot shows that all the para-substituted benzaldehydes are oxidised by the same mechanism. The Hammett plot is linear with positive ρ value. From the observed kinetic results a suitable mechanism was proposed.     

Kinetics and mechanism of oxidation of secondary alcohols by potassium bromate

The oxidation by Br(V) of propan-2-ol follows the rate law (?d[Br(V)]/dt) = k₄ [alcohol][Br(V)][H⁺]². The initial reaction is complicated by the presence of the product bromide ion. The reaction is composed of two second order reactions—the first, a comparatively slow one and the second stage, a faster reaction which is mainly bromine oxidation. The pure bromate oxidation can be followed by the initial addition of mercuric acetate which prevents the accumulation of bromine in the system under these conditions. The reaction rate does not depend on the nature and structure of the alcohol. A mechanism involving a slow rate-determining formation of an alkyl-bromate ester followed by a fast decomposition to the products is in accord with the observed results.     

Kinetics and mechanism of oxidation of ethanol,isopropanol and benzyl alcohol by chromium(VI) in perchloric acid medium

Chromium(VI) oxidation of some alkanols has been studied in perchloric acid medium. The reactions are first order with respect to [substrate] and [HCrO₄^-]. The order with respect to [H⁺]is between 1 and 2 for all the reactions. The activation parameters of the reactions have been calculated. A mechanism consistent with the above facts has been suggested. An attempt has been made to correlate the rate of the reactions with the structure of the substrates.     

Kinetics and mechanism of oxidation of substituted benzyl alcohols by polymer supported chromic acid

The reactions between substituted benzyl alcohols were found to proceed through ester formation. The ester thus formed decomposes in a slow step to produce chromium(IV). Since our oxidant was supported on a polymeric material the intermediate chromium(IV) will further oxidize another molecule of alcohol generating a free radical in a fast step. The free radical subsequently reacts with another oxidant site in the polymeric reagent in a fast step leading to the formation of chromium(V). The intermediate chromium(V) in the last step reacts with alcohol to produce an aldehyde. The activation parameters were also determined and the mechanism is predicted.     

Kinetics and mechanism of oxidation of allyl alcohol byN-bromosuccinimide

The kinetics of oxidation of allyl alcohol byN-bromosuccinimide (NBS) has been studied at 35 °C in aqueous medium. The reaction shows first order dependence on bothNBS and allyl alcohol. In fairly high acid concentration, there is no change in the rate of the reaction but at low acid concentration, the rate is considerably enhanced. There is no primary salt effect. At varying mercuric acetate concentrations, the rate constant remains the same. But in the absence of mercuric acetate, the rate is enhanced. The kinetic parameters,E _a,Arrhenius factorA, H, G and S have been calculated. A rate law in agreement with experimental results has been derived. A mechanism is proposed.

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Kinetik und Mechanismus der Oxidation von Allylalkohol mixN-Bromsuccinimid

Zusammenfassung Die Kinetik der Oxidation von Allylalkohol mitN-Bromsuccinimid (NBS) wurde bei 35 °C in wäßrigem Medium untersucht. Die Reaktion zeigt erste Ordnung gegenüberNBS und Allylalkohol. Bei relativ hoher Säurekonzentration zeigt sich keine Änderung der Reaktionsgeschwindigkeit, bei niedriger Säurekonzentration wird die Reaktionsgeschwindigkeit beträchtlich erhöht. Es wurde kein primärer Salzeffekt festgestellt. Bei varriierender Quecksilberacetatkonzentration bleibt die Reaktionsgeschwindigkeit gleich, bei Abwesenheit von Quecksilberacetat wird jedoch die Geschwindigkeitskonstante erhöht. Die kinetischen Parameter,E _a, derArrheniusfaktorA, H , G und S wurden bestimmt. Ein Geschwindigkeitsgesetz in Übereinstimmung mit den experimentellen Befunden wurde abgeleitet und ein Mechanismus vorgeschlagen.

     

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.     

Controlling the duality of the mechanism in liquid-phase oxidation of benzyl alcohol catalysed by supported Au-Pd nanoparticles

In the solvent-free oxidation of benzyl alcohol to benzaldehyde using supported gold-palladium nanoparticles as catalysts, two pathways have been identified as the sources of the principal product, benzaldehyde. One is the direct catalytic oxidation of benzyl alcohol to benzaldehyde by O(2), whereas the second is the disproportionation of two molecules of benzyl alcohol to give equal amounts of benzaldehyde and toluene. Herein we report that by changing the metal oxide used to support the metal-nanoparticles catalyst from titania or niobium oxide to magnesium oxide or zinc oxide, it is possible to switch off the disproportionation reaction and thereby completely stop the toluene formation. It has been observed that the presence of O(2) increases the turnover number of this disproportionation reaction as compared to reactions in a helium atmosphere, implying that there are two catalytic pathways leading to toluene.     

氯化铵三氧化铬在干反应中对苄醚的选择性氧化

本文报道氯化铵三氧化铬(ACC)是具有高选择性的氧化剂, 在无溶剂的干反应中, 可以把苄醚氧化成相应的苯甲酸酯, 且顶点满意的产率.     

Water oxidation intermediates applied to catalysis: benzyl alcohol oxidation

Four distinct intermediates, Ru(IV)═O(2+), Ru(IV)(OH)(3+), Ru(V)═O(3+), and Ru(V)(OO)(3+), formed by oxidation of the catalyst [Ru(Mebimpy)(4,4'-((HO)(2)OPCH(2))(2)bpy)(OH(2))](2+) [Mebimpy = 2,6-bis(1-methylbenzimidazol-2-yl) and 4,4'-((HO)(2)OPCH(2))(2)bpy = 4,4'-bismethylenephosphonato-2,2'-bipyridine] on nanoITO (1-PO(3)H(2)) have been identified and utilized for electrocatalytic benzyl alcohol oxidation. Significant catalytic rate enhancements are observed for Ru(V)(OO)(3+) (~3000) and Ru(IV)(OH)(3+) (~2000) compared to Ru(IV)═O(2+). The appearance of an intermediate for Ru(IV)═O(2+) as the oxidant supports an O-atom insertion mechanism, and H/D kinetic isotope effects support net hydride-transfer oxidations for Ru(IV)(OH)(3+) and Ru(V)(OO)(3+). These results illustrate the importance of multiple reactive intermediates under catalytic water oxidation conditions and possible control of electrocatalytic reactivity on modified electrode surfaces.     

Kinetics of oxidation of Indigo Carmine by potassium peroxydisulfate

The reaction is first order in potassium peroxydisulfate and zero order in Indigo Carmine. Hydrogen ions have no effect on the rate in the acidity range of 0.0–0.2 M. Allyl acetate inhibits the reaction. A radical chain mechanism is proposed.

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. 0 0,2 M . . .

     

Kinetics and mechanism of hemoglobin oxidation by nitroethane

In the present paper the process of oxyhemoglobin oxidation by nitroethane has been investigated. The main process is accompanied with numerous side reactions including oxidative denitration of nitroethane resulting in the generation of acetaldehyde and 1,1-dinitroethane. The latter product is formed under the action of nitrite ion which is the product of oxidative denitration of nitroethane. The chain radical mechanism of methemoglobin generation is proposed. The reaction of oxyhemoglobin with nitroethane is regarded as initiated autooxidation of oxyhemoglobin.     

碱性介质中二过碘酸合铜(III)配离子氧化四氢糠醇的动力学及机理

本文采用分光光度法研究了二过碘酸合铜(III)配离子在碱性介质中氧化四氢糠醇的动力学及机理. 结果表明反应对[Cu(III)]是一级, 对四氢糠醇是1.3级. 反应速率随体系中[OH^-]的增大而增大, 随过碘酸浓度的增大而减小, 反应体系加入硝酸钾盐时,速率增大, 有正盐效应. 在氮气保护下, 体系能够诱发丙烯酰胺聚合. 提出了一种含有自由基过程的反应机理, 据此导出了一个能够解释本文全部实验事实的速率方程. 求得了速率控制步骤的速率常数, 并给出了相应的活化参数.     

Novel oxidation of tetrasubstituted furans by pyridinium chlorochromate

A novel oxidation of tetrasubstituted furans with pyridinium chlorochromate has been studied and this has led to a convenient synthesis of 4-acetoxy-3-acetyl- or methoxycarbonyl-4-substituted phenylbut-3-en-2-one.     

Kinetics of oxidation and comproportionation reactions involving an oxammonium ion,benzyl alcohol and methyltrioxorhenium(VII)

The reactions of 4‐hydroxy‐2,2,6,6‐tetramethylpiperidinium N‐oxide, an oxammonium ion abbreviated R₂NO⁺, have been studied. The previously unreported triflate salt was used in this study because the anions of the usual chloride and bromide salts can themselves be oxidized. Reactions between R₂NO⁺ and alcohols produce ketones and aldehydes; the rate constant for PhCH₂OH is 4.4 × 10⁻³ L mol⁻¹ s⁻¹ in acetonitrile at 298 K. The immediate product is the hydroxylamine, R₂NOH, but its further comproportionation reaction with R₂NO⁺ yields the stable piperidinyl oxyl radical, R₂NO^·. The rate constant of this reaction is 1.78 × 10³ L mol⁻¹ s⁻¹ at 298 K. The possibility of using R₂NO⁺ and MTO as co‐catalysts for the oxidation of alcohols was explored, but the competitive rates are such that the resultant is not particularly attractive. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 381–385, 1999