Mechanistic aspects of oxidation of dextrose by N-bromophthalimide in acidic medium: a micellar kinetic study

Kinetic investigations of oxidation of dextrose by N-bromophthalimide (NBP) in acidic medium in the presence of mercuric(II) acetate as a scavenger have been studied. In both the absence and presence of surfactants, the oxidation kinetics of dextrose by NBP shows a first-order dependence on NBP, fractional order on dextrose, and negative fractional order dependence on sulfuric acid. The determined stoichiometric ratio was 1:1 (dextrose:NBP). The variation of Hg(OAC)₂ and phthalimide (reaction product) have an insignificant effect on reaction rate. Effects of surfactants, added acrylonitrile, added salts, and solvent composition variation have been studied. Activation parameters for the reaction have been evaluated from Arrhenius plot by studying the reaction at different temperature. The rate law has been derived on the basis of obtained data. A plausible mechanism has been proposed from the results of kinetic studies, reaction stoichiometry and product analysis. The role of anionic and non-ionic micelle was best explained by the Berezin’s model.     

Micellar catalysis of oxidation of glycolic acid by N-bromophthalimide

Catalysis of oxidation of glycolic acid by N-bromophthalimide by micelles of cetyltrimethylammonium bromide (CTAB) at 318 K was investigated. The observed value of critical micelle concentration of CTAB in the presence of other components was lower than those reported in the literature. The oxidation reaction was strongly catalyzed by cationic micelles of CTAB. The reaction rate increased with CTAB concentration until the steady state was achieved. The reaction kinetics corresponded to first, fractional and inverse fiactional orders with respect to changes of concentration of reaction components. Effects of solvent, phthalimide, mercuric acetate, and potassium chloride on the reaction kinetics were also studied. The micelle-catalyzed oxidation reaction was shown to fit Arrhenius equation. The experimental data were rationalized in terms of Menger-Portnoy model considering a distribution of the reactants between the micellar and aqueous phases.     

Kinetic study of oxidation of galactose by N-bromo phthalimide in the presence of cationic micelle in acidic medium

The kinetics of micellar catalyzed oxidation of galactose by N-bromophthalimide was studied in the presence of acidic medium at 308?K. The oxidation reaction exhibits first-order kinetics with respect to oxidant (N-bromophthalimide), fractional order with respect to substrate (galactose) and positive fractional order with respect to HClO₄ on the rate of reaction. The rate of the reaction increased with decreasing the dielectric constant of the medium. With a progressive increase in the concentration of CTAB, the rate of reaction increased and after reaching peak k _obs, decreased at higher concentrations of CTAB. There catalytic roles are best explained by Berezin??s model. The influence of salts on the reaction rate was also studied. The various activation parameters have been calculated. The rate constant and binding constant with the surfactant have also been evaluated. A suitable mechanism consistent with the experimental findings has been proposed.     

Kinetics and mechanism of oxidation of aspirin by bromamine-T,N-bromosuccinimide,and N-bromophthalimide

The kinetics of the oxidation of aspirin (ASP) by bromamine-T (BAT), N-bromosuccinimide (NBS), and N-bromophthalimide (NBP) has been studied in aqueous perchloric acid at 303 K. The oxidation reaction follows identical kinetics with first-order in [oxidant], fractional-order in [ASP], and inverse fractional-order in [H⁺]. Under identical experimental conditions the extent of oxidation with different oxidizing agents is in the order: NBS>BAT>NBP. The rate decreased with decreasing dielectric constant of the medium. The variation of ionic strength and the addition of the reaction products and halide ions had no significant effect on the reaction rate. The solvent isotope effect was studied using D₂O. Kinetic parameters were evaluated by studying the reaction at different temperatures. The reaction products were identified by GC–MS. The proposed reaction mechanism and the derived rate law are consistent with the observed kinetic data. Formation and decomposition constants for ASP-oxidant complexes have been evaluated. Decarboxylation, bromination, and loss of acetic acid gave 2,4,6-tribromophenol. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 407–414, 1998     

Micelle Catalyzed Oxidation of D-Mannose by Cerium (IV) in Sulfuric Acid

Kinetics of D-mannose oxidation by cerium (IV) was studied in a sulfuric acid medium at 40°C both in absence and presence of ionic micelles. In both cases, the rate of the reaction was first-order in D-mannose and cerium (IV), which decreased with increasing [H₂SO₄]. This suggested that the redox reaction followed the same mechanism. The reaction proceeded through formation of an intermediate complex, which was proved by kinetic method. The complex underwent slow unimolecular decomposition to a free radical that reacted with cerium (IV) to afford the product. The catalytic role of cationic cetyltrimethylammonium bromide (CTAB) micelles was best explained by the Menger-Portnoy model. The study of the effect of CTAB also indicated that a negatively charged species was the reactive form of cerium (IV). From the kinetic data, micelle-cerium (IV) binding and rate constants in micellar medium were evaluated. The anionic micelle of sodium dodecyl sulfate plays no catalytic role. The oxidation has the rate expression: -d[Ce(IV)]=k1Kc1[D-mannose][Ce(IV)]dt Different activation parameters for micelle catalyzed and uncatalyzed paths were also calculated and discussed.     

硫酸存在时N-溴代苯二甲酰亚胺对甘露糖的胶束催化氧化

The kinetics of micellar-catalyzed oxidation of mannose by N-bromophthalimide was studied in the presence of sulfuric acid at 313 K. The orders of reaction with respect to [mannose], [oxidant], and [H+] were found to be fractional, first, and negative fractional order, respectively. Anionic micelles of sodiumdodecyl sulfate showed a partial inhibitory effect, while cationic micelles of cetyltrimethylammonium bromide increased the reaction rate with the same kinetic behavior. The reaction was catalyzed by cationic micelles, because of favorable electrostatic/thermodynamic/hydrophobic/hydrogen bonding between reactants and cationic micelles. Their catalytic roles are best explained by Berezin’s model. A variation of [phthalimide] showed that the rate of reaction decreased with increasing [phthalimide]. It was observed that, an increase of [mercuric acetate] had no effect on reaction velocity. The influence of salts on the reaction rate was also studied. The rate constant (kW ), binding constants (KS+KO), and corresponding activation parameters (Ea, ⊿H#, ⊿S#, and ⊿G#) were determined. A detailed mechanism with associated reaction kinetics is presented and discussed.     

Rhodium(III) as a homogeneous catalyst for the oxidative decolorization of ethyl orange with aqueous acidic chloramine-T: a spectrophotometric, kinetic and mechanistic study

The kinetics and mechanism of sodium N-chloro-p-toluenesulfonamide oxidative decolorization of ethyl orange (EO) in aqueous perchloric acid have been studied at 303 K in the presence of rhodium(III) chloride as catalyst. The reaction exhibits first-order dependence on [EO]_o and a fractional-order dependence on [CAT]_o, [H⁺] and [Rh^III]. The dielectric effect is positive. The stoichiometry of the reaction was found to be 1:1, and the oxidation products of EO were identified as N-(4-diethylamino-phenyl)-hydroxylamine and 4-nitroso-benzenesulfonic acid. The rhodium(III)-catalyzed reaction is about fourfold faster than the uncatalyzed reaction. The proposed mechanism and derived rate law are in agreement with the observed kinetic results.     

Mechanistic studies of oxidation of maltose and lactose by [H2OBr]+ in presence of chloro-complex of Rh(III) as homogeneous catalyst

Kinetic studies in homogeneously Rh(III)-catalyzed oxidation of reducing sugars, i.e. maltose and lactose, by N-bromoacetamide (NBA) in the presence of perchloric acid have been made at 40 °C using mercuric acetate as Br⁻ ion scavenger. The results obtained for the oxidation of both reducing sugars show first-order dependence of the reactions on NBA at its low concentrations, which shifts towards zero-order at its higher concentrations. First-order kinetics in [Rh(III)] and zero-order kinetics in [reducing sugar] were observed. Positive effect of [Cl⁻] was observed in the oxidation of both maltose and lactose. Order of reaction was found to be one and half (1.5) throughout the variation of [H⁺] in the oxidation of both maltose and lactose. An increase in the rate of reaction with the decrease in [Hg(OAc)₂] and [NHA] was observed for both the redox systems. The rate of oxidation is unaffected by the change in ionic strength (μ) of the medium. The main oxidation products of the reactions were identified as formic acid and arabinonic acid in the case of maltose and formic acid, arabinonic acid and lyxonic acid in the case of lactose. A common mechanism for the oxidation of both maltose and lactose, showing the formation of most reactive activated complex, [RhCl₄(H₃O)H₂OBr]⁺, and an unreactive complex, [RhCl₄(H₂O)(H₂OBrHg)]²⁺, has been proposed. Various activation parameters have also been calculated and on the basis of these parameters, a suitable explanation for the reaction mechanism has been given.     

Effect of Anionic Surfactant on the Oxidation of DL-Aspartic Acid by N-Bromophthalimide: A Kinetic Study

The kinetics of oxidation of DL-Aspartic acid (Asp) by N-bromophthalimide (NBP) was studied in the presence of sodium dodecyl sulfate (SDS) in acidic medium at 308 K. The rate of reaction was found to have first-order dependence on [NBP], fractional order dependence on [Asp] and inverse fractional order dependence on [H⁺]. The addition of reduced product of the oxidant, that is, [Phthalimide] has decreased the rate of reaction. The rate of reaction increased with increase in inorganic salts concentration, whereas a change in [Cl^?], ionic strength of the medium and [Hg(OAc)₂] had no effect on the oxidation velocity. The rate of reaction decreased with a decrease in dielectric constant of the medium. COOH-CH₂-CN was identified as the main oxidation product of the reactions. The various activation parameters have been computed. A suitable reaction mechanism consistent with the experimental findings has been proposed. The micelle-binding constant has been calculated.     

Effect of surfactant micelles on the kinetics of oxidation of D‐fructose by cerium(IV) in sulfuric acid medium

Kinetics of the oxidation of D ‐fructose by cerium(IV) has been investigated both in the absence and presence of surfactants (cetyltrimethylammonium bromide, CTAB, and sodium dodecyl sulfate, SDS) in sulfuric acid medium. The reaction exhibits first‐order kinetics each in [cerium(IV)] and [D ‐fructose] and inverse first order in [H₂SO₄]. The Arrhenius equation is found to be valid for the reaction between 30–50°C. A detailed mechanism with the associated reaction kinetics is presented and discussed. While SDS has no effect, CTAB increases the reaction rate with the same kinetic behavior in its presence. The catalytic role of CTAB micelles is discussed in terms of the pseudophase model proposed by Menger and Portnoy. The association constant K_s that equals to 286 mol^?1 dm³ is found for the association of cerium(IV) with the positive head group of CTAB micelles. The effect of inorganic electrolytes (Na₂SO₄, NaNO₃, NaCl) has also been studied and discussed. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 38: 18–25, 2006     

Inhibitory effect of ruthenium(III) on the oxidation of dimethyl sulphoxide byN-bromosuccinimide andN-bromophthalimide. A novel observation

Ru^III exerts an inhibitory effect on the oxidation of DMSO byN-bromosuccinimide and byN-bromophthalimide in the presence of Hg(OAc)₂ in aqueous AcOH at 15°C. The reaction order is unity with respect to the oxidant and substrate, but less than one at low substrate concentrations; fractional for higher concentrations. The effect of the ionic strength of the medium is negligible, while that of dielectric constant is positive. Added acrylonitrile is not polymerised. Addition of mineral acid increases the reaction rate. A probable mechanism is proposed, rationalising the inhibitory effect of Ru^III.     

Kinetics of hydrolysis of procaine in aqueous and micellar media

The kinetics of alkaline hydrolysis of procaine under the pseudo–first‐order condition ([OH^?] ? [procaine]) has been carried out. N,N‐Diethylaminoethanol and p‐aminobenzoate anion were obtained as the hydrolysis product. The rate of hydrolysis was found to be linearly dependent upon [NaOH]. The addition of cationic cetyltrimethylammonium bromide (CTAB), dodecyltrimethylammonium bromide (DDTAB) and tetradecyltrimethylammonium bromide, and anionic sodium dodecyl sulfate (SDS) micelles inhibited the rate of hydrolysis. The maximum inhibitive effect on the reaction rate was observed for SDS micelles, whereas among the cationic surfactants, CTAB inhibited most. The variation in the rate of hydrolysis of procaine in the micellar media is attributed to the orientation of a reactive molecule to the surfactant and the binding constant of procaine with micelles. The rate of hydrolysis of procaine is negligible in DDTAB micelles. The observed results in the presence of cationic micelles were treated on the basis of the pseudophase ion exchange model. The results obtained in the presence of anionic micelles were treated by the pseudophase model, and the various kinetic parameters were determined. © 2012 Wiley Periodicals, Inc. Int J Chem Kinet 45: 1–9, 2013     

Combination of micellar and chemical catalysis as a means of enhancing the sensitivity of catalytic kinetic determinations

The combined effects of micellar and chemical catalysis were studied to improve the features of catalytic kinetic determinations. The bromate oxidative coupling reaction of p-phenetidine with catechol, catalysed by vanadium(V), was studied in the presence and absence of micelles of cetylpyridinium chloride (CPC). This cationic surfactant increased the reaction rate, which in turn resulted in an increase in the sensitivity by an order of magnitude in the kinetic determination of vanadium(V). A detailed study of the kinetics of both reactions is reported. The mechanism by which CPC and vanadium(V) exert their action was elucidated and the role of micellar media in catalytic kinetic methods is discussed.     

The features of the kinetics of radical reactions of quinone imines with 2-mercaptobenzothiazole

Kinetics of the reactions of N-phenyl-1,4-benzoquinone monoimine and N,N′-diphenyl-1,4-benzoquinone diimine with 2-mercaptobenzothiazole in chlorobenzene at T = 343 K has been studied by using kinetical spectrophotometry method (periodic spectral measurements and/or monitoring the wavelengths of the absorption band of quinone imines in the visible region). Two general features of the reactions, namely, radical mechanism and the existence of two steps were found. Kinetic features depend on the structure of a quinone imine. A reaction between N,N′-diphenyl-1,4-benzoquinone diimine and 2-mercaptobenzothiazole at first (initial) steps proceeds in an autoinhibition mode and has two independent channels, one of which being radical-chain. The addition of an initiator strongly accelerates the reaction only at the initial step, on completion of which the reaction rate decreases significantly and do not depend on the presence of the initiator. This testifies to the proceeding of the reaction by a non-chain mechanism subsequently to the initial step. The interaction involving N-phenyl-1,4-benzoquinone monoimine proceeds by a radical non-chain mechanism from the very beginning up to the end, and at the initial steps it proceeds in the autoaccelerating mode. The initiator has no influence on the reaction rate. For the process of the interaction of N,N′-diphenyl-1,4-benzoquinone monoimine and 2-mercaptobenzothiazole in the presence of 4-hydroxydiphenylamine, a radical mechanism was proposed, that serves to describe the kinetic features of the reaction and to obtain a quantitative estimation of some of its kinetic parameters.     

Kinetics and Mechanism of Oxidation of l‐Histidine by Permanganate Ions in Sulfuric Acid Medium

The reaction kinetics for the oxidation of l ‐histidine by permanganate ions have been investigated spectrophotometrically in sulfuric acid medium at constant ionic strength and temperature. The order with respect to permanganate ions was found to be unity and second in acid concentration, whereas a fractional order is observed with respect to histidine. The reaction was observed to proceed through formation of a 1:1 intermediate complex between oxidant and substrate. The effect of the acid concentration suggests that the reaction is acid catalyzed. Increasing the ionic strength has no significant effect on the rate. The influence of temperature on the rate of reaction was studied. The presence of metal ion catalysts was found to accelerate the oxidation rate, and the order of effectiveness of the ions was Cu²⁺ > Ni²⁺ > Zn²⁺. The final oxidation products were identified as aldehyde (2‐imidazole acetaldehyde), ammonium ion, manganese(II), and carbon dioxide. Based on the kinetic results, a plausible reaction mechanism is proposed. The activation parameters were determined and discussed with respect to a slow reaction step.     

Micellar catalyzed hydrolysis of mono-2,3-dichloroaniline phosphate

The kinetics of micellar catalyzed hydrolysis of mono-2,3-dichloroaniline phosphate in the presence of different surfactants has been studied at 303?K. The rate of reaction has been found to be first order with respect to both [substrate] and [HCl]. The cationic micelles of cetylpyridinium chloride (CPC), anionic micelles of di-octyl sodium sulphosuccinate (AOT), and non-ionic micelles of polyoxyethylene sorbitan monooleate (Tween 80) enhanced the rate of reaction to a maximum value and after that the increase in concentration of surfactant decreased the reaction rate. The applicability of different kinetic models has been tested to explain the observed micellar effects. The various thermodynamic activation parameters (E_a, ΔH^≠, ΔS^≠, ΔG^≠) have been evaluated. The added salts viz. KCl, KNO₃, K₂SO₄ enhanced the rate of reaction in the presence of CPC, AOT, and Tween 80 micelles. The kinetic parameters were determined from the rate (surfactant) profile and a suitable mechanism consistent with the experimental finding has been proposed.     

Kinetics and Mechanism of the Oxidation of 4-Oxo-4-arylbutanoic Acids by N-bromophthalimide in Aqueous Acetic Acid Medium

The kinetics of oxidation of a series of substituted 4-oxobutanoic acids (Y–C₆H₄COCH₂CH₂COOH: Y = H, OCH₃, CH₃, C₆H₅, Cl, Br or NO₂) by N-bromophthalimide have been studied in aqueous acetic acid medium at 30 °C. The total reaction is second-order, first-order each in oxidant and substrate. The oxidation rate increases linearly with [H⁺], establishing the hypobromous acidium ion, H₂O⁺Br, as the reactive species. A variation in ionic strength has no effect on the reaction rate. The order of reactivity among the studied 4-oxoacids is: 4-methoxy > 4-methyl > 4-phenyl > 4-H > 4-Cl > 4-Br > 3-NO₂. The effect of changes on the electronic nature of the substrate reveals that there is a development of positive charge in the transition state. The activation parameters have been computed from Arrhenius and Eyring plots. Based on the kinetic results, a suitable mechanism has been proposed.     

Mechanism of nitration of nitrogen-containing heterocyclic <Emphasis Type="Italic">N</Emphasis>-acetonyl derivatives. General approach to the synthesis of <Emphasis Type="Italic">N</Emphasis>-dinitromethylazoles

A general synthetic procedure for the synthesis of N-dinitromethyl derivatives of nitrogen-containing heterocycles has been developed. The procedure includes the destructive nitration of heterocyclic N-acetonyl derivatives of tetrazoles, 1,2,4- and 1,2,3-triazoles, pyrazoles, imidazoles and their bicyclic analogs, as well as imides of carboxylic and sulfonic acids and substituted hydrazines with mixtures of sulfuric and nitric acids. The kinetic study of the reaction mechanism was performed using UV and NMR spectroscopy. It was found that the NO₂ groups were sequentially introduced into the methylene fragment by the addition of the nitronium ion to multiple bonds of intermediate enols followed by hydrolysis of the acetyl moiety. The rate and direction of the enolization (due to the CH₂ and CH₃ groups) of the N-acetonyl compounds in sulfuric acid solutions were determined by the study of the deuterium exchange kinetics. The synthesis of the N-dinitromethyl compounds is complicated by side reactions, such as the decomposition of intermediate α-nitroketone, the nitration of the methyl group in the acetonyl moiety, and the nitration of the dinitromethyl products to trinitromethyl derivatives.     

Mechanism of the acid hydrolysis of aromatic o-carboxyamides and relative imides

The kinetics of N-phenylphthalamic acid and of N-phenylphthalimide hydrolysis in aqueous solutions of sulfuric acid has been studied. A reaction mechanism is proposed implying that unreactive forms of the reactant appear by protonization of the amide bond at the carbonyl oxygen and by dissociation of the o-carboxyl group (N-phenylphthalamic acid). Attack of the nonprotonized amide bond by the hydroxonium ion is suggested to be the rate-limiting step.     

Kinetics and mechanism of oxidation of L-Alanine by <Emphasis Type="Italic">N</Emphasis>-bromophthalimide in the presence of sodium dodecyl sulfate

The kinetics of oxidation of L-Alanine (Ala) by N-bromophthalimide (NBP) was studied in the presence of an anionic surfactant, sodium dodecyl sulfate, in acidic medium at 308 K. The rate of reaction was found to have first-order dependence on [NBP], fractional order dependence on [Ala] and inverse fractional order dependence on [H⁺]. The addition of reduced product of the oxidant [Phthalimide] has decreased the rate of reaction. The rate of reaction increased with increase in inorganic salts concentration i.e., [Cl⁻] and [Br⁻], whereas a change in ionic strength of the medium and [Hg(OAc)₂] had no effect on oxidation velocity. The rate of reaction decreased with a decrease in dielectric constant of the medium. CH₃CN was identified as the main oxidation product of the reaction. The various activation parameters have been computed and suitable mechanism consistent with the experimental findings has also been proposed. The micelle-binding constant has been calculated. Published in Russian in Kinetika i Kataliz, 2009, Vol. 50, No. 3, pp. 386–396. The article is published in the original.