nan Puttaswamy

Oxidation of isoniazid by N-haloarenesulfonamidates in alkaline medium: A kinetic and mechanistic study

The kinetics of oxidation of Isoniazid (INH) by sodium N-haloarenesulfonamidates, chloramine-T (CAT), bromamine-T (BAT), chloramine-B (CAB), and bromamine-B (BAB), has been studied in alkaline medium at 303 K. The oxidation reaction follows identical kinetics with a first-order dependence on each [oxidant] and [INH] and an inverse fractional-order on [OH−:]. Addition of the reaction product (p-toluenesulfonamide or benzenesulfonamide) had no significant effect on the reaction rate. Variation of ionic strength and addition of halide ions have no influence on the rate. There is a negative effect of dielectric constant of the solvent. Studies of solvent isotope effects using D2O showed a retardation of rate in the heavier medium. The reaction was studied at different temperatures, and activation parameters have been computed from the Arrhenius and Eyring plots. Isonicotinic acid was identified as the oxidation product by GC-MS. A two-pathway mechanism is pro-posed in which RNHX and the anion RNX− interact with the substrate in the rate-limiting steps. The mechanism proposed and the derived rate laws are consistent with the observed kinetics. The rate of oxidation of INH increases in the order: BAT > BAB > CAT > CAB. This effect is mainly due to electronic factors.

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.

Palladium(II)‐Catalyzed Oxidation of Primary Amines by Bromamine‐T in Alkaline Medium: A Kinetic and Mechanistic Study

Oxidations of n‐propyl, n‐butyl and n‐hexylamines by bromamine‐T (BAT), catalyzed by Pd(II), in alkaline medium have been kinetically studied at 30 °C. The reaction rate shows a first‐order dependence on [BAT], a fractional‐order dependence each on [NaOH] and [Pd(II)], and an inverse fractional‐order dependence on [Cl–]. The reaction rate is independent of [amine]. The addition of the reduction product of BAT, p‐toluenesulfonamide, and the variation of dielectric constant of the solvent have no effect on the rate. The catalytic constants were calculated at different temperatures. Activation parameters were evaluated.

Kinetics of oxidation of acidic amino acids by sodium N-bromobenzenesulphonamide in acid medium: A mechanistic approach

Kinetics of oxidation of acidic amino acids (glutamic acid (Glu) and aspartic acid (Asp)) by sodium N-bromobenzenesulphonamide (bromamine-B or BAB) has been carried out in aqueous HClO4 medium at 30°C. The rate shows first-order dependence each on [BAB]o and [amino acid]o and inverse first-order on [H+]. At [H+] > 0·60 mol dm−3, the rate levelled off indicating zero-order dependence on [H+] and, under these conditions, the rate has fractional order dependence on [amino acid]. Succinic and malonic acids have been identified as the products. Variation of ionic strength and addition of the reaction product benzenesulphonamide or halide ions had no significant effect on the reaction rate. There is positive effect of dielectric constant of the solvent. Proton inventory studies in H2O-D2O mixtures showed the involvement of a single exchangeable proton of the OH− ion in the transition state. Kinetic investigations have revealed that the order of reactivity is Asp > Glu. The rate laws proposed and derived in agreement with experimental results are discussed.

Ruthenium(III) Catalyzed Oxidation of Aliphatic Primary Amines by Bromamine-T in Hydrochloric Acid Medium: A Kinetic Study

Abstract The kinetics of the ruthenium(III) catalyzed oxidation of the aliphatic primary amines n-propylamine, n-butylamine and isoamylamine, by sodium N-bromo-p-toluenesulfonamide or bromamine-T (BAT) in HCl medium has been studied in the temperature range 298–313 K. The reaction rate shows a first-order dependence each on BAT, amine, and ruthenium(III). The reaction also shows an inverse fractional- and inverse first-order dependence on acid at low and high [HCl] ranges, respectively. Added halide ions and p-toluenesulfonamide (reduction product of BAT), and variation of ionic strength of the solvent medium have no effect on the rate. The activation parameters have been evaluated. Mechanisms consistent with the kinetic data have been proposed. The protonation constant of monobromamine-T has been evaluated to be 29 ± 2. A Taft LFE relationship is observed for the ruthenium(III) catalyzed reaction with ρ∗ = −4.6 indicating that the electron donating groups enhance the reaction rate. An isokinetic relation...

Kinetics and mechanism of oxidation of chloramphenicol by 1-chlorobenzotriazole in acidic medium

Chloramphenicol (CAP) is an antibiotic drug having a wide spectrum of activity. The kinetics of oxidation of chloramphenicol by 1-chlorobenzotriazole (CBT) in HClO4 medium over the temperature range 293–323 K has been investigated. The reaction exhibits first-order kinetics with respect to [CBT]o and zero-order with respect to [CAP]o. The fractional-order dependence of rate on [H+] suggests complex formation between CBT and H+. It fails to induce polymerization of acrylonitrile under the experimental conditions employed. Activation parameters are evaluated. The observed solvent isotope effect indicates the absence of hydride transfer during oxidation. Effects of dielectric constant and ionic strength of the medium on the reaction rate have been studied. Oxidation products are identified. A suitable reaction scheme is proposed and an appropriate rate law is deduced to account for the observed kinetic data.

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 I = -12.6, indicating that the electron-donating groups enhance the reaction rate. An isokinetic relationship is observed with I² = 350 K, indicating that enthalpy factors control the reaction rate.

Selective and an efficient oxidative conversion of glutathione to glutathione disulfide with N-bromosuccinimide in aqueous acidic solution: kinetic and mechanistic chemistry

Oxidative conversion of thiols to disulfides is an important chemical transformation in organic synthesis. A tripeptide, glutathione (GSH), composed of glutamate, cysteine and glycine, has been found to be the most abundant low molecular weight thiol in most biological systems. Its importance in mammal systems is believed to be related to its functions in oxidative metabolism and detoxification. It is noted that despite the importance of this substrate, less information is available in the literature on the oxidation of this substrate viewed from its kinetic and mechanistic studies. N-Bromosuccinimide (NBS) is a mild and selective oxidant for many organic compounds, and hence, it has been used as an oxidant for the present redox system. Consequently, the kinetics of oxidation of GSH with NBS in aqueous HClO4 medium has been investigated at 283 K. The reaction rate exhibits first-order dependence on [NBS]o and fractional-order dependence each on [GSH]o and [H+]. The effect of added succinimide, ionic strength and dielectric constant of the medium on the rate of the reaction has been studied. The solvent isotope effect was studied using D2O. The reaction was studied at different temperatures and thermodynamic parameters have been computed. Glutathione disulfide is characterized as the oxidation product of GSH. The protonated species RN+HBr (here R = (CH2O)2−) of the NBS is assumed to be the reactive oxidizing species. The reaction constants involved in the mechanism were evaluated. The observed results have been explained by a plausible mechanism, and the related rate law has been deduced.

Oxidation of vanillin and related compounds by sodium N-chloro-p- toluenesulfonamide in acid medium: A kinetic and mechanistic approach

The kinetics of oxidation of vanillin, vanillyl alcohol, vanillylamine hydrochloride and vanillyl mandelic acid (hereafter abbreviated as substrate) by N-chloro-p-toluenesulfonamide or chloramine–T (CAT) in HClO4 medium has been investigated at 30±0.1°C. The oxidation reaction follows identical kinetics with first-order in [CAT]o, fractional order in [substrate]o, and inverse fractional-order in [H+]. Variation of ionic strength and addition of the reaction product, p-toluenesulfonamide, or halide ions had no significant effect on reaction rate. Decrease in dielectric constant of the medium decreases the rate. The solvent isotope effect was studied in D2O medium. The reaction does not induce polymerization of acrylonitrile. Michaelis-Menten type of kinetics has been proposed and activation parameters for the rate-limiting step as well as overall reaction have been computed. The decomposition constants of substrate-oxidant complexes have been evaluated. Under comparable experimental conditions, the rate of oxidation increases in the following order vanillin>vanillylamine hydrochloride>vanillyl alcohol>vanillylmandelic acid. An isokinetic relationship is observed with β=339 K, indicating enthalpy as a controlling factor. Vanillic acid was identified as the oxidation product of each substrate and was confirmed by IR and GC-MS data. A general mechanism involving the formation of a complex between substrate and the conjugate acid (CH3C6H4SO2NHCl) of the oxidant has been proposed. The derived rate law is in agreement with the experimental results.

Oxidation of some catecholamines by sodium N-chloro-p-toluenesulfonamide in acid medium: A kinetic and mechanistic approach

The kinetics of the oxidation of five catecholamines viz., dopamine (A), L-dopa (B), methyldopa (C), epinephrine (D) and norepinephrine (E) by sodium N-chloro-p-toluenesulfonamide or chloramine-T (CAT) in presence of HClO4 was studied at 30±0.1 °C. The five reactions followed identical kinetics with a first-order dependence on [CAT]o, fractional-order in [substrate]o, and inverse fractional-order in [H+]. Under comparable experimental conditions, the rate of oxidation of catecholamines increases in the order D>E>A>B>C. The variation of ionic strength of the medium and the addition of p-toluenesulfonamide or halide ions had no significant effect on the reaction rate. The rate increased with decreasing dielectric constant of the medium. The solvent isotope effect was studied using D2O. A Michaelis-Menten type mechanism has been suggested to explain the results. Equilibrium and decomposition constants for CAT-catecholamine complexes have been evaluated. CH3C6H4SO2NHCl of the oxidant has been postulated as the reactive oxidizing species and oxidation products were identified. An isokinetic relationship is observed with β=361 K, indicating that enthalpy factors control the reaction rate. The mechanism proposed and the derived rate law are consistent with the observed kinetics.