Kinetics and mechanism of the bromination of crotonic acid by N-bromosuccinimide

The bromination of crotonic acid by N-bromosuccinimide (NBS) is first order with respect to crotonic acid and zero order with respect toNBS and the rate of the reaction changes linearly with hydrogen ion concentration. The thermodynamic parameters have also been calculated.     

Kinetic and mechanistic studies of some aliphatic amines' oxidation by sodium N‐bromo‐p‐toluenesulfonamide in hydrochloric acid medium

Oxidations of n‐propyl, n‐butyl, isobutyl, and isoamyl amines by bromamine‐T (BAT) in HCl medium have been kinetically studied at 30°C. The reaction rate shows a first‐order dependence on [BAT], a fractional‐order dependence on [amine], and an inverse fractional‐order dependence on [HCl]. The additions of halide ions and the reduction product of BAT, p‐toluenesulfonamide, have no effect on the reaction rate. The variation of ionic strength of the medium has no influence on the reaction. Activation parameters have been evaluated from the Arrhenius and Eyring plots. Mechanisms consistent with the preceding kinetic data have been proposed. The protonation constant of monobromamine‐T has been evaluated to be 48 ± 1. A Taft linear free‐energy relationship is observed for the reaction with ρ* = −12.6, indicating that the electron‐donating groups enhance the reaction rate. An isokinetic relationship is observed with β = 350 K, indicating that enthalpy factors control the reaction rate. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 776–783, 2000     

Mechanistic study of osmium(VIII) promoted oxidation of crotonic acid by aqueous alkaline solution of potassium bromate

Kinetics and mechanism of the Os(VIII) catalysed oxidation of crotonic acid (CA) by KBrO₃ in alkaline medium have been investigated. Zero order dependence in [KBrO₃] was observed, while first order with respect to CA in its lower concentration range tends to zero order at its higher concentration range. The order in [Os(VIII)] was found to be unity and a positive effect of [OH⁻] was observed. Variation of the ionic strength (μ) and dielectric constant of the medium and addition of Hg(OAc)₂ (used as Br⁻ scavenger) had an insignificant effect on the rate of reaction. Thermodynamic parameters have also been calculated and reported. A suitable mechanism consistent with the observed kinetic results has been suggested and the related rate law deduced.     

Kinetics and mechanism of esterification of epoxy resin in presence of triphenylphosphine

The kinetics of esterification of bisphenol‐A based epoxy resin with acrylic acid in presence of triphenylphosphine has been studied. The reaction exhibits a first‐order rate dependence with respect to [Epoxy] and [Catalyst]. A first‐order dependence of rate with respect to [Acid] has been observed during a particular kinetic run. However, a retarding effect of [Acid] on the rate has been observed by increasing the initial concentration of acid. A suitable mechanism consistent with the kinetic data is proposed and discussed. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 280–285, 2004     

Ruthenium(III)‐catalyzed oxidation of cyclopentanol and cyclohexanol by N‐bromoacetamide

Kinetic investigations on Ru(III)‐catalyzed oxidation of cyclopentanol and cyclohexanol by acidic solution of N‐bromoacetamide (NBA) in the presence of mercury(II) acetate as a scavenger have been carried out in the temperature range of 30–45°C. Similar kinetics was followed by both the cyclic alcohols. First‐order kinetics in the lower concentration range of NBA was observed to tend to zero order at its higher concentrations. The reaction exhibits a zero‐order rate dependence with respect to each cyclic alcohol, while it is first order in Ru^III. Increase in [H⁺] and [Cl^?] showed positive effect, while successive addition of acetamide exhibited negative effect on the reaction rate. Insignificant effect of sodium perchlorate, D₂O, and mercury(II) acetate on the reaction velocity was observed. Cationic bromine has been proposed as the real oxidizing species. Various thermodynamic parameters have been computed. A suitable mechanism in agreement with the kinetic observations has been proposed. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 37: 275–281, 2005     

Kinetics and mechanism of oxidation of sugars by quinquevalent vanadium in binary mixture solvents of DMSO–water and acetic acid–water in H2SO4 medium

The kinetics of oxidation of aldosugars and ketosugar by quinquevalent vanadium in binary mixtures of DMSO–water and acetic acid–water in sulfuric acid medium have been studied. The reaction is first order in both oxidant and substrate. The effect of acidity on the reaction kinetics has been determined. The effect of acidity shows a clear difference. The ketose has a unit dependence, whereas aldoses have a 0.5 dependence in H₀. The role of solvent in these reactions has also been studied, and the effect of temperature on these reactions has been determined. A suitable mechanism has been postulated taking all the observed facts into consideration.     

Kinetics and mechanism of oxidation of neutral α ‐amino acids by sodium N‐chloro‐p‐toluenesulfonamide in acid medium

Kinetics of oxidation of α ‐amino acids, glycine, valine, alanine, and phenylalanine, by sodium N‐chloro‐p‐toluenesulfonamide or chloramine‐T (CAT) has been investigated in HClO₄ medium at 30°C. The rate shows first‐order dependence on both CAT and amino acid concentrations and an inverse first‐order on [H⁺]. The variation of ionic strength and the addition of p‐toluenesulfonamide and Cl^? ion had no effect on the reaction rate. Decrease of dielectric constant of the medium by increasing the MeOH content decreased the rate. Rate studies in D₂O medium showed the inverse solvent‐isotope effect of k_D2O/k_H2O=0.50. Proton‐inventory studies were carried out using H₂O–D₂O mixtures. The activation parameters have been computed. The proposed mechanism and the derived rate law are consistent with the observed kinetic data. An isokinetic relationship is observed with β=323 K, indicating enthalpy as a controlling factor. The rate of oxidation increases in the following order: Gly < Val < Phe < Ala. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 34: 49–55, 2002     

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.     

Synthesis,kinetics, and mechanism of bromophenols by N‐bromophthalimide in aqueous acetic acid

The kinetics and mechanism of bromination of phenol and its substituents, viz. 4‐chlorophenol, 4‐bromophenol, 4‐methylphenol, and 4‐methoxyphenol by N‐bromophthalimide (NBP) in the presence of mercuric acetate in the temperature range of 303–318 K in aqueous acetic acid medium have been investigated. The reaction follows first‐order dependence on [NBP] and fractional order dependence of rate on [Phenol]. The activation parameters have been evaluated, and based on the observed kinetic results the probable mechanism has been proposed. Observed kinetic features and Hammett's reaction constant (ρ) suggests that bromination occurs through electrophilic substitution of bromonium ion (Br⁺) into the aromatic ring in the transition state. Large negative entropy of activation values probably suggests the rigid nature of transition state.     

Kinetics and mechanistic aspects on electron‐transfer process for permanganate oxidation of poly(ethylene glycol) in aqueous acidic solutions in the presence and absence of Ru(III) catalyst

The kinetics and mechanism of oxidation of poly(ethylene glycol) (PEG) by the permanganate ion as a multiequivalent oxidant in aqueous perchlorate solutions at an ionic strength of 2.0 mol dm⁻³ has been investigated spectrophotometrically. The reaction kinetics was found to be of complex in nature. The pseudo–first‐order plots showed curves of inverted S‐shape, consisting of two distinct stages throughout the entire course of reaction. The first stage was relatively slow, followed by a fast reaction rate at longer time periods. The first‐order dependence in [MnO₄⁻], fractional first‐order dependence in [H⁺], and fractional first‐order kinetics in the PEG concentration for the first stage have been revealed in the absence of the Ru(III) catalyst. The influence of the Ru(III) catalyst on the oxidation kinetics has been examined. The oxidation was found to be catalyzed by the added Ru(III) catalyst. The First‐order dependence on the catalyst and zero order with respect to the oxidant concentrations have been observed. The kinetic parameters have been evaluated, and a tentative reaction mechanism consistent with the kinetic results is suggested and discussed.     

Kinetics and mechanism of the ruthenium(III)-catalyzed oxidation of hydroxy-acids byN-bromosuccinimide

Summary The kinetics of the Ru^III-catalyzed oxidation of the hydroxy acids; lactic, tartaric, malic and citric acids byN-bromosuccinimide in HClO₄ and in the presence of Hg(OAc)₂ have been studied. The reactions exhibit a first order rate dependence with respect to the oxidant and zeroth order rate dependence with respect to substrate. The rate is retarded by [H⁺], accelerated at law Ru^III concentrations but independent of [Ru^III] at higher Ru^III concentrations. A mechanism consistent with the observed kinetic data is proposed.     

Kinetics of oxidation of pantothenic acid by chloramine‐T in perchloric acid and in alkaline medium catalyzed by OsO4: A mechanistic approach

Kinetics of oxidation of pantothenic acid (PA) by sodium N‐chloro‐p‐toluenesulfonamide or chloramine‐T (CAT) in the presence of HClO₄ and NaOH (catalyzed by OsO₄) has been investigated at 313 K. The stoichiometry and oxidation products are same in both media; however, their kinetic patterns were found to be different. In acid medium, the rate shows first‐order dependence on [CAT]_o, fractional‐order dependence on [PA]_o, and inverse fractional‐order on [H⁺]. In alkaline medium, the rate shows first‐order dependence each on [CAT]_o and [PA]_o and fractional‐order dependence on each of [OH^?] and [OsO₄]. Effects of added p‐toluenesulfonamide and halide ions, varying ionic strength, and dielectric constant of medium as well as solvent isotope on the rate of reaction have been investigated. Activation parameters were evaluated, and the reaction constants involved in the mechanisms have been computed. The proposed mechanisms and the derived rate laws are consistent with the observed kinetics. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 37: 201–210, 2005     

Kinetics and mechanism of the oxidation of formic and oxalic acids by quinolinium fluorochromate

Kinetics and mechanism of oxidation of formic and oxalic acids by quinolinium fluorochromate (QFC) have been studied in dimethylsulphoxide. The main product of oxidation is carbon dioxide. The reaction is first-order with respect to QFC. Michaelis-Menten type of kinetics were observed with respect to the reductants. The reaction is acid-catalysed and the acid dependence has the form: k_obs =a +b[H⁺]. The oxidation of α-deuterioformic acid exhibits a substantial primary kinetic isotope effect (k_H/k_D = 6.01 at 303 K). The reaction has been studied in nineteen different organic solvents and the solvent effect has been analysed using Taft’s and Swain’s multiparametric equations. The temperature dependence of the kinetic isotope effect indicates the presence of a symmetrical cyclic transition state in the rate-determining step. Suitable mechanisms have been proposed.     

Oxidation of some primary amines by bromamine-B in alkaline medium: A kinetic and mechanistic study

The kinetics of oxidation of the aliphatic primary amines, n-propylamine, n-butylamine, and isoamylamine, by sodium N-bromobenzenesulfonamide or bromamine-B (BAB) in sodium hydroxide medium has been studied at 35° C. The reaction rate shows a first-order dependence each on [BAB] and [amine], and fractional order on [OH^-]. Additions of halide ions and the reduction product of BAB (benzenesulfonamide), and variation of ionic strength and dielectric constant of the medium do not have any significant effect on the reaction rate. Activation parameters have been evaluated. A Taft linear free-energy relationship is observed for the reaction with ρ* = −3.0 and δ = − 2.0 indicating that electron-donating groups enhance the rate. An isokinetic relationship is observed with β = 393 K indicating that enthalpy factors control the rate. The existence of the relationship has been supported by the Exner criterion. Mechanisms consistent with the observed kinetic data have been proposed. © 1996 John Wiley & Sons, Inc.     

Mechanism of oxidation of some aliphatic ketones by N-bromosuccinimide in acidic media

Kinetics of the oxidation of methyl n-propyl ketone and methyl isobutyl ketone by N-bromosuccinimide (NBS) have been studied in perchloric acid media in presence of mercuric acetate. A zero order dependence to N-bromosuccinimide and a first order dependence to both ketones and hydrogen ion concentrations have been observed. Sodium perchlorate, mercuric acetate and succinimide additions have negligible effect while methanol addition has a positive effect on the reaction rate. A solvent isotope effect (k₀D₂O/K₀H₂O = 2.3-2.7 and 2.4-2.8 for MeCOn.pr and MeCoi-Bu, respectively) has been observed at 35°. Kinetic investigations have revealed that the order of reactivity is methyl n-propyl ketone > methyl isobutyl ketone. Various thermodynamic parameters have been computed and corresponding 1,2-diketones were found to be the products. A suitable mechanism in conformity with the above observations has been proposed.     

Electron transfer reactions of V(IV) with Cl(I), Br(I) and I(I). A kinetic study

A kinetic study on the oxidation of V(IV) by chloramine-T (CAT) at pH 6.85 by N-bromo succinimide (NBS) in aqueous acetic acid–perchloric acid media and by N-iodo succinimide (NIS) in aqueous perchloric acid medium has been carried out. In all the systems studied the order with respect to the oxidant is unity. NBS and CAT oxidation reactions exhibited Michaelis–Menten type kinetics, and the NIS study indicated unit dependence on [substrate]. Independence on acidity has been observed in the case of CAT and NBS reactions, but NIS reactions exhibited inverse unit dependence on [acid]. Novel solvent influences have been noticed in the case of CAT reactions, but with NIS and NBS reactions retardation in the rate has been observed with an increase in the percentage of acetic acid. Plausible mechanisms consistent with the results have been postulated, and suitable rate laws in consonance with the postulated mechanisms have been derived.     

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 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 of cyclohexene oxidation by <Emphasis Type="Italic">p</Emphasis>-quinones in aqueous-organic solutions of cationic palladium(II) complexes

A kinetic study of cyclohexene oxidation by p-quinones in water-acetonitrile solutions of cationic Pd(II) complexes has been carried out for the first time. The observed kinetic regularities (dependence of the initial rate on the HClO₄ and p-benzoquinone concentrations) and the shape of the kinetic curves differ radically from those for the chloride systems. The unsteady-state process can be described only under the assumption that complexes of reduced palladium species with quinones are catalytically active forms. The role of solvated palladiumcarbenium ions in particular steps of the mechanism is discussed.     

Kinetics and mechanism of the oxidation of diols by pyridinium bromochromate

The kinetics of oxidation of four vicinal diols, four nonvicinal diols, and one of their monoethers by pyridinium bromochromate (PBC) have been studied in dimethyl sulfoxide. The main product of oxidation is the corresponding hydroxyaldehyde. The reaction is first-order with respect to each the diol and PBC. The reaction is acid-catalyzed and the acid dependence has the form: k_obs=a+b[H⁺]. The oxidation of [1,1,2,2-²H₄]ethanediol exhibited a primary kinetic isotope effect (k_H/k _D=6.70 at 298 K). The reaction has been studied in 19 organic solvents including dimethyl sulfoxide and the solvent effect has been analyzed using multiparametric equations. The temperature dependence of the kinetic isotope effect indicates the presence of a symmetrical transition state in the rate-determining step. A suitable mechanism has been proposed. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 285–290, 1998.