No abstract

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 [oxidant] o and a fractional-order dependence on each [diclofenac] o 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 þ and Br þ 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.

p-Aminoazobenzene (PAAB) is one of the important monoazo dyes and its oxidation kinetic study is of much use in understanding the mechanistic profile of PAAB in redox reactions. Consequently, the kinetics of oxidation of PAAB by sodium N-chlorobenzenesulfonamide or chloramine-B (CAB) in HClO 4 medium and in NaOH medium catalyzed by ruthenium(III) chloride (Ru III ) have been investigated at 298 K. U.v.-vis spectrophotometry was used as a basic analytical approach in this study. Under an identical set of experimental conditions, the reactions of PAAB-CAB in HClO 4 medium were facile, but the reactions became too slow to be studied in alkaline medium and hence ruthenium(III) chloride has been used as a catalyst in alkaline medium. The stoichiometry (1:2) and oxidation products (nitrosobenzene and p-nitrosoaniline) are the same in both media, but the kinetic and mechanistic patterns were found to be different. The experimental rate laws obtained are:III ] y in alkaline medium, where x and y are less than unity. The reaction was examined with reference to changes in (a) concentration of benzenesulfonamide, (b) concentration of added neutral salts, (c) ionic strength, (d) dielectric permitivity and (e) solvent isotope effect. The reaction was also studied at different temperatures and the overall activation parameters have been evaluated. The oxidation reaction fails to induce the polymerization of added acrylonitrile. C 6 H 4 SO 2 NHCl and C 6 H 4 SO 2 NCl ) have been postulated as the reactive oxidizing species in acidic and alkaline media, respectively. It was found that the reactions are nearly 20 times faster in acid medium in comparison with alkaline medium. It was also observed that ruthenium(III) was an efficient catalyst for the facile oxidation of PAAB by CAB in alkaline medium by making the reaction go twelve-fold faster than the uncatalyzed reactions. The catalytic constant (K C ) has been calculated at different temperatures and the values of activation parameters with respect to ruthenium(III) have also been evaluated in alkaline medium. The observed results have been explained by plausible mechanisms and the relative rate laws have been deduced.

In this work, ZnO nanocrystals (NCs) have been effectively synthesized by a simple, efficient and cost-effective method using coconut husk extract as a novel fuel. The synthesized NCs are characterized by UV-Vis, XRD, FT-IR, SEM, EDX, Raman and PL studies. The obtained ZnO were found to be UV-active with a bandgap of 2.93 eV. The X-ray diffraction pattern confirms the crystallinity of the ZnO with hexagonally structured ZnO with a crystallite size of 48 nm, while the SEM analysis reveals the hexagonal bipyramid morphology. Photocatalytic activities of the synthesized ZnO NCs are used to degrade methylene blue and metanil yellow dyes.

The kinetics of oxidative decolorization of acid orange 8 (AO8) by chloramine-T and bromamine-T in HClO 4 medium has been investigated spectrophotometrically (λ max = 490 nm) at 298 K. Kinetic runs were executed under pretend first-order conditions of [oxidant] o >> [AO8] o. Under identical experimental conditions, reactions with both the oxidants follow identical kinetics with a first-order dependence on each [oxidant] o and [AO8] and a fractional-order dependence on [HClO 4 ]. Stoichiometry of the reaction was found to be 1:1 and the oxidation products were identified. The reaction was studied at dissimilar temperatures and activation parameters have been computed. Effects of p-toluenesulfonamide, halide ions, ionic strength and dielectric constant of the medium have been investigated. Reaction mixture fails to induce polymerization of acrylonitrile. The rate of oxidation of AO8 is about twofold faster with BAT as compared to CAT. This may be endorsed to the diversity in electrophilicities of Cl + and Br + ions and also the van der Waal's radii of chlorine and bromine. Authentic mechanism and associated rate law have been deliberated for the observed kinetics.

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 [BAB] o and less than unity order dependence on [TA] o. 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 [BAB] o and [Pd(II)] and zero-order with respect to [TA] o. 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 (K C) has been calculated at different temperatures and activation parameters with respect to Pd(II) catalyst have also been evaluated. The conjugate acid C 6 H 5 SO 2 NHBr and the anion C 6 H 5 SO 2 N − 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.

KEYWORDSThe kinetics of oxidative decolorization of amido black (AB, Naphthol blue black) by chloramine-T (CAT) and bromamine-T (BAT) in acidic medium has been investigated spectrophotometrically (λmax = 618 nm) at 298 K. Kinetic runs were performed under pseudo first-order conditions of [Oxidant] . Stoichiometry of the reaction was found to be 1:4 and the oxidation products were identified. The reaction was studied at different temperatures and various activation parameters have been computed. Effects of p-toluenesulfonamide, halide ions, ionic strength and dielectric constant of the medium have been investigated. Reaction mixture fails to induce polymerization of acrylonitrile. The rate of oxidation of AB is about three-fold faster with BAT as compared to CAT. This may be attributed to the difference in electrophilicity of Cl + and Br + ions and also the Vander Waals radii of chlorine and bromine. Plausible mechanism and related rate law have been deliberated for the observed kinetics.

The ZnO-based ternary heterostructure ZnO/Eu2O3/NiO nanoparticles are synthesized using waste curd as fuel by a simple one-pot combustion method. The as-synthesized heterostructure is characterized by using various spectroscopic and microscopic techniques including X-ray diffraction, UV–vis, FTIR, SEM, and TEM analyses. The photocatalytic activity of the ternary nanocomposite was tested for the photodegradation of methylene blue (MB) under solar light irradiation. The results have revealed that the ternary ZnO/Eu2O3/NiO photocatalyst exhibits excellent performance toward the photocatalytic degradation of the studied dye. Optimization studies revealed that the synthesized heterostructure exhibited a pH-dependent photocatalytic activity, and better results are obtained for specific concentrations of dye and catalysts. Among the different light sources employed during the study, the catalyst was found to possess the best degradation efficiency in visible light.