Oxidation of tetracaine hydrochloride by chloramine-b in acid medium: Kinetic modeling

Tetracaine hydrochloride (TCH) is one of the potent local anaesthetics. A kinetic study of oxidation of tetracaine hydrochloride by sodium N-chlorobenzenesulfonamide (chloramine-B or CAB) has been carried in HClO 4 medium at 303 K. The rate shows first-order dependence on CAB o, shows fractional-order dependence on substrate o, and is self-governing on acid concentration. Decrease of dielectric constant of the medium, by adding methanol, increased the rate. Variation of ionic strength and addition of benzenesulfonamide or NaCl have no significant effect on the rate. The reaction was studied at different temperatures and the activation parameters have been evaluated. The stoichiometry of the reaction was found to be 1: 5 and the oxidation products were identified by spectral analysis. The conjugate free acid C6H5SO2NHCl of CAB is postulated as the reactive oxidizing species. The observed results have been explained by plausible mechanism and the related rate law has been deduced. © 2014 Jayachamarajapura Pranesh Shubha and Puttaswamy

N-oxidation of pyrazines by bromamine-B in perchloric acid medium: Kinetic and mechanistic approach

Kinetic investigations on the oxidation of pyrazine and four 2-substituted pyrazines viz., 2-methylpyrazine, 2-ethylpyrazine, 2-methoxypyrazine and 2-aminopyrazine by bromamine-B (BAB) to the respective N-oxides have been studied in HClO4 medium at 303 K. The reactions show identical kinetics being first-order each in BABo and pyrazineo, and a fractional-order dependence on H+. Effect of ionic strength of the medium and addition of benzenesulfonamide or halide ions showed no significant effect on the reaction rate. The dielectric effect is positive. The solvent isotope effect was studied using D2O. The reaction has been studied at different temperatures and activation parameters for the composite reaction have been evaluated from the Arrhenius plots. The reaction showed 1:1 stoichiometry and the oxidation products of pyrazines were characterized as their respective N-oxides. Under comparable experimental conditions, the oxidation rate of pyrazines increased in the order: 2-aminopyrazine > 2-methoxypyrazine > 2-ethylpyrazine > 2-methylpyrazine > pyrazine. The rates correlate with the Hammett � relationship and the reaction constant � was found to be -0.8, indicating that electron donating centres enhance the rate of reaction. An isokinetic temperature of β = 333 K, indicated that the reaction was enthalpy controlled. A mechanism consistent with the experimental results has been proposed in which the rate determining step is the formation of an intermediate complex between the substrate and the diprotonated species of the oxidant. The related rate law in consistent with observed results has been deduced

Kinetics and mechanistic chemistry of oxidation of butacaine sulfate by chloramine-b in acid medium

Butacaine sulfate is an ester of p-aminobenzoic acid which has been widely used as a local anaesthetic and it is a long standing agent particularly for spinal anaesthesia. For this reason, a kinetic study of oxidation of butacaine sulfate by sodium N-chlorobenzenesulfonamide (chloramine-B or CAB) has been carried out in HClO4 medium at 303 K in order to explore this redox system mechanistic chemistry. The rate shows a firstorder dependence on both CABo, and substrateo, and a fractional-order dependence on acid concentration. Decrease of dielectric constant of the medium, by adding methanol, increases the rate of the reaction. Variation of ionic strength and addition of benzenesulfonamide or NaCl have no significant effect on the rate. The reaction was studied at different temperatures and the activation parameters have been evaluated. The stoichiometry of the reaction has been found to be 1:2 and the oxidation products have been identified by spectral analysis. The observed results have been explained by plausible mechanism and the related rate law has been deduced

Palladium(II)-catalyzed oxidation of tranexamic acid by bromamine-B in alkaline medium and uncatalyzed reaction in acid medium: A study of kinetic and mechanistic chemistry

Tranexamic acid (TA) possess antifibrinolytic properties and finds extensive applications in pharmaceuticals. Its oxidation-kinetic study is of much significance in understanding the mechanistic profile of TA in biological systems. In this context, a systematic kinetic study of palladium(II) (Pd(II)) catalyzed oxidation of TA by sodium N-bromobenzenesulfonamide or bromamine-B (BAB) in alkaline medium and uncatalyzed reaction in perchloric acid medium at 303 K was investigated. In acid medium, the reaction exhibits a first-order dependence of rate on BABo and less than unity order dependence on TAo. The reaction rate shows inverse less than unity order dependence with respect to H+. In alkaline medium, the reaction shows first-order dependence on both BABo and Pd(II) and zero-order with respect to TAo. The order with respect to OH - is less than unity. Activation parameters have been evaluated. The oxidation reactions are nearly 10-fold faster in acid medium in comparison with alkaline medium. In alkaline medium, the Pd(II) catalyzed reactions are about 6-fold faster than the uncatalyzed reaction. Further, the catalytic constant (KC) has been calculated at different temperatures and activation parameters with respect to Pd(II) catalyst have also been evaluated. The conjugate acid C6H5SO2NHBr and the anion C 6H5SO2N-Br of BAB have been postulated as the reactive oxidizing species in acid and alkaline media, respectively. The proposed mechanisms and derived rate laws are in agreement with the observed kinetics. © 2010 Elsevier B.V. All rights reserved

Ruthenium(III)-catalyzed and uncatalyzed kinetic studies on the oxidation of sulfanilic acid by chloramine-T in perchloric acid medium: A mechanistic approach

The kinetics of the oxidation of sulfanilic acid (SAA) by sodium N-chloro-p-toluenesulfonamide (CAT) in the presence and absence of ruthenium(III) chloride have been investigated at 303 K in perchloric acid medium. The reaction shows a first-order dependence on CAT o and a non-linear dependence on both SAA o and HClO 4 for both the ruthenium(III)-catalyzed and uncatalyzed reactions. The order with respect to Ru III is unity. The effects of added p-toluenesulfonamide, halide, ionic strength, and dielectric constant have been studied. Activation parameters have been evaluated. The rate of the reaction increases in the D 2O medium. The stoichiometry of the reaction was found to be 1:1 and the oxidation product of SAA was identified as N-hydroxyaminobenzene-4-sulfonic acid. The ruthenium(III)-catalyzed reactions are about four-fold faster than the uncatalyzed reactions. The protonated conjugate acid (CH 3C 6H 4SO 2NH 2Cl +) is postulated as the reactive oxidizing species in both the cases. © 2008 Springer Science+Business Media B.V

Kinetics and mechanism of oxidation of coumarin and substituted coumarins by chloramine-b in hydrochloric acid medium

The kinetics of oxidation of coumarin (see Equation (1)) and four substituted coumarins, viz. 7-methoxycoumarin, 7-ethoxycoumarin, 7-hydroxycoumarin and 7-nitrocoumarin, to the corresponding o-hydroxycinnamic acids by chloramine-B (CAB) have been studied at 298 K. Under comparable experimental conditions, the reaction rate shows a first-order dependence each upon CABo and coumarino, and individually less than unit order dependence on H+ and Cl-. Addition of benzenesulfonamide retards the reaction rate and the dielectric effect is positive. Variation of ionic strength of the medium does not influence the rate but the rate increases with increase in dielectric constant of the medium. The solvent isotope effect was studied using D2O. The reaction was studied at different temperatures and activation parameters have been evaluated. The stoichiometry of the reaction was found to be 1:1 and the oxidation products of coumarins were identified as their corresponding o-hydroxycinnamic acids. The rate of oxidation of coumarins increases in the order: 7-hydroxycoumarin > 7-ethoxycoumarin > 7-methoxycoumarin > coumarin > 7-nitrocoumarin. The rates satisfactorily correlate with the Hammett a relationship and the reaction constant p is - 0.04, which signifies that electron-donating groups enhance the rate and the electron-withdrawing group retards the rate. An isokinetic relationship was observed with β= 348 K, which showed the reaction to be enthalpy controlled. A mechanism consistent with the experimental results is proposed in which the rate-determining step is the formation of an intermediate complex between the substrate and molecular chlorine. The related rate law has been deduced and the decomposition constants were evaluated. © Science Reviews 2000 Ltd

Kinetics and mechanism of sodium N-halo-p-toluenesulfonamides oxidation of diclofenac in alkaline medium

Diclofenac belongs to a class of drugs called nonsteroidal antiinflammatory drugs. The kinetics and mechanism of oxidation of diclofenac by sodium N-halo-p-toluenesulfonamides viz., chloramine-T and bromamine-T in NaOH medium have been studied at 293 K. Under comparable experimental conditions, reactions with both the oxidants follow identical kinetics with a first-order dependence on each oxidanto and a fractional-order dependence on each diclofenaco and NaOH. Activation parameters have been computed. N-hydroxyldiclofenac is identified as the oxidation product of diclofenac. Michaelis-Menten type of mechanism has been suggested. The rate of oxidation of diclofenac is about four-fold faster with bromamine-T when compared with chloramine-T. This may be attributed to the difference in electrophilicities of Cl+ and Br+ ions and also the van der Waal's radii of chlorine and bromine. Plausible mechanism and related rate law have been designed for the observed kinetics. © 2009 American Institute of Chemical Engineers

Oxidative conversion of thiourea and N-substituted thioureas into formamidine disulfides with acidified chloramine-T: A kinetic and mechanistic approach

The kinetics of oxidation of thiourea and N-substituted thioureas namely: N-methylthiourea, N-allylthiourea N-phenylthiourea and N-tolylthiourea to the corresponding formamidine disulfides by sodium N-chloro-p-toluenesulfonamide or chloramine-T (CAT) in the presence of HClO4 has been investigated at 278K. The reactions follow identical kinetics for all thioureas, being first order each with respect to CATo, Thioureao and H+. Ionic strength of the medium and addition of p-toluenesulfonamide or halide ions have negligible influence on the rate. The solvent isotope effect has been studied using D2O in the case of the oxidation of thiourea. Decrease in the dielectric constant of the medium by adding methanol decreases the rate. The reactions were studied at different temperatures, and the composite activation parameters have been computed. An isokinetic relationship was observed with β =314K, indicating that enthalpy factors control the reaction rate. Under comparable experimental conditions, the rate of oxidation of thioureas increases in the order: N-allylthiourea > N-phenylthiourea > N-methylthioureathiourea > N-tolylthiourea. A mechanism involving the interaction of conjugate acid (CH3C6H4 SO 2NHCl) and substrate giving an intermediate complex, in a slow step, has been suggested. The derived rate law is in agreement with the observed kinetics

Kinetics of oxidation of procaine hydrochloride by sodium N-chlorobenzenesulfonamide in acid and alkaline media: A mechanistic approach

A kinetic study of oxidation of procaine hydrochloride (one of the potent local anaesthetics) by sodium N-chlorobenzenesulfonamide (chloramine-B or CAB) has been carried out in HClO 4 (30°C) and NaOH (20°C) media. In acid medium, the rate shows first-order dependence on CAB o and fractional-order dependence on substrate o. But, it is independent of the acid. In alkaline medium, the rate exhibits first-order dependence each on CAB o and substrate o, and inverse fractional-order on OH -. Activation parameters have been evaluated. The reaction is found to be faster in alkaline medium in comparison with acid medium. The conjugate free acid C 6H 5SO 2NHCl of CAB is postulated as the reactive oxidizing species in both the media. The observed results have been explained by plausible mechanisms and the related rate laws have been deduced

Kinetics and reactivities of ruthenium(III)- and osmium(VIII)-catalyzed oxidation of ornidazole with chloramine-T in acid and alkaline media: A mechanistic approach

Ornidazole is an antiparasitic drug having a wide spectrum of activity. Literature survey has revealed that no attention has been paid towards the oxidation of ornidazole with any oxidant from the kinetic and mechanistic view point. Also no one has examined the role of platinum group metal ions as catalysts in the oxidation of this drug. Such studies are of much use in understanding the mechanistic profile of ornidazole in redox reactions and provide an insight into the interaction of metal ions with the substrate in biological systems. For these reasons, the Ru(III)- and Os(VIII)-catalyzed kinetics of oxidation of ornidazole with chloramine-T have been studied in HCl and NaOH media, respectively at 313 K. The oxidation products and kinetic patterns were found to be different in acid and alkaline media. Under comparable experimental conditions, in Ru(III)-catalyzed oxidation the rate law is -dCAT/dt = k CAToornidazoleoxH+ -yRu(III)z and it takes the form -dCAT/dt = k CAToornidazoleoxOH- yOs(VIII)ArSO2NH2-z for Os(VIII)-catalyzed reaction, where x, y and z are less than unity. In acid medium, 1-chloro-3-(2-methyl-5-nitroimidazole-1-yl)propan-2-one and in alkaline medium, 1-hydroxy-3-(2-methyl-5-nitroimidazole-1-yl)propan-2-one were characterized as the oxidation products of ornidazole by GC-MS analysis. The reactions were studied at different temperatures and the overall activation parameters have been computed. The solvent isotope effect was studied using D2O. Under identical set of experimental conditions, the kinetics of Ru(III) catalyzed oxidation of ornidazole by CAT in acid medium have been compared with uncatalyzed reactions. The relative rates revealed that the catalyzed reactions are about 5-fold faster whereas in Os(VIII) catalyzed reactions, it is around 9 times. The catalytic constant has been calculated for both the catalysts at different temperatures and activation parameters with respect to each catalyst have been evaluated. The observed experimental results have been explained by plausible mechanisms. Related rate laws have been worked out. © 2009 Elsevier B.V. All rights reserved