Showing papers by "Ajaya Kumar Singh published in 2009"

Mechanistic study of novel oxidation of paracetamol by chloramine-T using micro-amount of chloro-complex of Ir(III) as a homogeneous catalyst in acidic medium

Abstract: The mechanistic study of iridium (III)-catalyzed oxidation of paracetamol has been studied by sodium N-chloro-p-toluenesulfonamide (chloramine-T) in aqueous perchloric acid medium at 308 K. The reaction followed first-order kinetics with respect to [chloramine-T], [paracetamol] and [Cl − ] in their lower concentrations range, tending to zero-order at their higher concentrations. First-order kinetics with respect to [Ir(III)] was observed for the oxidation of paracetamol. The rate of reaction decreased with increasing [H + ] and [p-toluene sulphonamide, PTS] were observed for the oxidation of paracetamol. The variation of the ionic strength of the medium had no significant effect on the rate of the reaction. The first-order rate constant increased with decrease in the dielectric constant of the medium. The values of rate constants observed at five different temperatures were utilized to calculate the activation parameters. The reaction between chloramine-T and paracetamol in acid medium exhibits 1:2 stoichiometry. A plausible mechanism from the results of kinetic studies, reaction stoichiometry and product analysis has been proposed.

Kinetics and Mechanism of Ru(III)-Catalyzed Oxidation of Paracetamol by Chloramine-T in Aqueous Acidic Medium

Abstract: The present paper deals with the kinetics and mechanism of Ru(III)-catalyzed oxidation of paracetamol by chloramine-T (CAT) in aqueous perchloric acid medium at 303 K. The experimental result shows a first order dependence on paracetamol at its low concentrations, but tending towards zeroth order at its higher concentrations. The reactions follow a first order rate dependence with respect to oxidant [CAT] and [Ru(III)]. The reaction showed negative fractional-order dependence on the rate for [H+] and p-toluenesulphonamide. Variation in [Cl−] and ionic strength of the medium did not bring about any significant change on the rate of reaction. The decrease in the reaction rate with decrease in the dielectric constant of the medium was observed in the oxidation of paracetamol. Kinetic and equivalence studies together with product analysis, observed effect of dielectric constant of the medium on the rate of reaction and activation parameters furnished a basis for the formation of a common reaction mechanism for the Ru(III)-catalyzed oxidation of paracetamol by CAT in the acidic medium.

Kinetics and mechanism of oxidation of L-Alanine by N-bromophthalimide in the presence of sodium dodecyl sulfate

Abstract: 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.

A Novel Oxidation of Valine by N-Bromophthalimide in the Presence of Ruthenium(III) Chloride as a Homogeneous Catalyst

Abstract: Kinetics of Ruthenium(III) [Ru(III)] chloride catalyzed oxidation of valine (Val) has been studied by N-bromophthalimide (NBP) in the acidic medium at 35 °C. The reaction rate follows first-order and zero-order dependence with respect to [NBP] and [Val]. First-order kinetics was observed for Ru(III) chloride at low range of concentrations and tending towards zero-order at higher concentrations. A negative effect was observed for [H+] and [phthalimide], while a positive effect was observed for [Cl−] on the reaction rate. Hg(OAc)2, ionic strength (I), and dielectric constant (D) of the medium did not change significantly the reaction rate. The rate constants as a function of temperature (298–318 K) were used to calculate activation parameters of the oxidation of Val by NBP. A plausible mechanism was proposed to explain the results of kinetic studies, reaction stoichiometry and product analysis.

Kinetics and mechanism of oxidation of β-Alanine by N-bromophthalimide in the presence of Ru(III) chloride as homogenous catalyst in acidic medium

Abstract: The kinetics of Ru(III) chloride-catalyzed oxidation of β-Alanine (NH3+CH2CH2COOH, β-Ala) by N–bromophthalimide (NBP) in aqueous perchloric acid medium was studied at 35 °C. The rate law followed a first-order and zero-order dependence with respect to [NBP] and [β-Ala], respectively. The reaction followed first-order kinetics with respect to [Ru(III)] chloride at a range of low concentrations while the order changed from first- to zero-order at high concentration of [Ru(III)] chloride; demonstrating the catalytic effect for the oxidation of β-Ala by NBP. The rate decreased with increase in acidity. Chloride ions positively influenced the rate of the reaction. Neither phthalimide (NHP) nor Hg(II) influenced the reaction rate. Ionic strength (I) and dielectric constant (D) of the medium had no significant effect on the rate. Activation parameters of the reactions were determined by studying the reaction at different temperatures (30–50 °C). The colorimetric, FTIR, and GC-MS techniques were used to identify methyl cyanide (CH3CN) and CO2 as products of the reaction. In the reaction, approximately 2.3 moles of NBP oxidized one mole of β-Ala. A reaction scheme of the oxidation of β-Ala by NBP in the presence of Ru(III) chloride was found to be in consistent with the rate law and the reaction stoichiometry.

Effect of Cationic Micelle on the Kinetics of Oxidation of Citric Acid by N-Bromophthalimide in Acidic Medium

Abstract: Kinetics of the oxidation of citric acid (CA) by N-bromophthalimide (NBP) has been studied in the presence of cationic surfactant cetyltrimethylammonium bromide (CTAB) at 35°C. The CMC value is lower than those given in the literature for aqueous solutions of CTAB without added electrolyte. The reaction is strongly catalyzed by cationic micelle, CTAB with a progressive increase in CTAB concentration the reaction rate increased, at higher concentration constancy in the rate constant was observed. The reaction follows first and fractional order kinetics in NBP and citric acid, respectively. The reaction follows inverse fractional order with respect to perchloric acid. The Arrhenius equation is found to be valid for the reaction. A detailed mechanism with the associated reaction kinetics is discussed. The catalytic role of CTAB micelles is discussed in terms of the Menger and Portnoy model.

Kinetic Study of Oxidation of DL-Serine by N-Bromophthalimide in the Presence of Sodium Dodecyl Sulfate

Abstract: The kinetics of oxidation of DL-serine (Ser) 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 [Ser] and inverse fractional order dependence on [H+]. The addition of reduced product of the oxidant [Phthalimide] and [Hg(OAc)2] has no effect on the rate of reaction. The change in ionic strength of the medium had no effect on oxidation velocity. The rate of reaction increased with increasing [Br−] and decreased with increasing [Cl−]. The rate of reaction decreased with decrease in dielectric constant of the medium. OHCH2CN was identified as the main oxidation product of the reactions. The various activation parameters have been computed. A suitable mechanism consistent with the experimental findings has been proposed. The micelle-binding constant has been calculated.

Effect of Ionic Micelle on the Oxidation of Diethylene Glycol by N-Bromophthalimide

Abstract: The kinetics of oxidation of diethylene glycol (DEG) by N-bromophthalimide (NBP) in the acidic medium in the presence of cetyltrimethylammonium bromide (CTAB), that is, cationic surfactant has been studied In addition to kinetic experiments, conductivity measurements have also been done to obtain critical micelle concentration and other thermodynamic properties The kinetic observations indicate fractional order dependence with respect to Substrate and inverse fractional order with respect to perchloric acid (HClO4) The reaction has a first order dependence on NBP Reaction is strongly catalyzed by CTAB, mercuric acetate (CH3COO)2Hg and phthalimide (NHP) found to inhibit the rate of reaction The applicability of kinetic model, Berezin's model, has been tested to explain the observed micellar effect On the basis of experimental findings, a pertinent mechanism is proposed

Kinetic and Mechanistic Study of the Influence of Micelles on the Oxidation of Acetone by N-Bromophthalimide in Aqueous Acetic Acid Medium

Abstract: The effect of cationic micelles of Cetyltrimethylammonium bromide (CTAB) and anionic micelles of Sodium dodecyl Sulphate (SDS) on the kinetics of oxidation of acetone by N-Bromophthalimide (NBP) was studied iodometrically at 308 K. In addition to kinetic experiments, conductivity measurements have also been done to obtain critical micelle concentration and other thermodynamic properties. The kinetic observations indicate fractional order and first order dependence, with respect to [Acetone] and [NBP] respectively. Cationic surfactant (CTAB) strongly catalysed the oxidation of acetone in aqueous acetic acid medium and typical kobs and [CTAB] profile was observed i.e. with the progressive increase in [CTAB], the reaction rate increased, at higher concentration constancy in kobs was observed, whereas anionic surfactant (SDS) was found to show no considerable effect on reaction rate. Mercuric acetate and phthalimide exhibited nil effect on the reaction rate. The presence of inorganic salts (KCl, KBr)...