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 kinetics of oxidation of five amines viz., ethylenediamine (EDA), diethylenetriamine (DETA), triethylenetetramine (TETA), aminoethylpiperazine (AEP) and isophoronediamine (IPDA) by sodium N-chloro-p-toluenesulfonamide or chloramine-T (CAT) in the presence of HCl and Ru(III) chloride was studied at 303 K. The five reactions followed identical kinetics and the experimental rate law is ratez , where x, y and z are fractions. A variation of the ionic strength or dielectric constant of the medium and the addition of halide ions and ptoluenesulfonamide had no significant effect on the rate of the reaction. The solvent isotope effect has been studied in D 2 O medium. The activation parameters have been evaluated from the Arrhenius plots. Under comparable experimental conditions, the rate of oxidation of amines increases in the order: AEP > TETA > DETA > EDA > IPDA. An isokinetic relationship is observed with β = 377 K, indicating enthalpy as a controlling factor.Oxidation products were identified. CH 3 C 6 H 4 SO 2 + NH 2 Cl of the oxidant has been postulated as the reactive oxidizing species. Further, the kinetics of Ru(III)-catalysed oxidation of these amines have been compared with unanalyzed reactions (in the absence of Ru(III) catalyst) and found that the catalysed reactions are 2-3-fold faster. The catalytic constant (K C ) was also calculated for each amine at different temperatures from the plots of log K C against 1/T, values of activation parameters with respect to the catalyst have been evaluated. The observed results have also been explained by a plausible mechanism and the related rate law has been deduced.

The kinetics of the oxidation of two tricyclic antidepressants (TCA) namely, imipramine (IMP) and clomipramine (CLM) with sodium N-chloro-p-toluenesulfonamide or chloramine-T (CAT) in HClO4 medium was studied at 300 K. The two reactions followed identical kinetics with a first-order dependence of rate on [CAT]o and fractional order dependence on [TCA]o. The reaction is catalyzed by H+ ions with a fractional order dependence. The reaction was studied at different temperatures and activation parameters were evaluated. The reaction constants involved in the mechanism were computed. The solvent isotope effect was studied using D2O. Addition of p-toluenesulfonamide retards the reaction rate. The rate increased with decreasing dielectric constant of the medium. Variation of ionic strength of the medium and addition of halide ions (Cl- or Br-) showed no effect on the rate. The stoichiometry of the reaction was found to be 1:1 and the oxidation products were identified as imipramine-5-N-oxide and clomipramine-5-N-oxide. The rate of oxidation of IMP is faster than CLM. The observed results have been explained in terms of a mechanism and a relevant rate law has been deduced.

Cephalosporins areβ-lactam antibiotics, and the important drugs of this group are cephalexin, cefadroxil and cephradine. In the present research, the kinetics and mechanism of oxidation of cephalexin (CEX), cefadroxil (CFL), and cephradine (CPD) with chloramine-T (CAT) in alkaline medium were investigated at 301 K. All the three oxidation reactions follow identical kinetics with a first-order dependence each on [CAT]oand [substrate]o. The reaction is catalyzed by hydroxide ions, and the order is found to be fractional. The dielectric effect is negative. Proton inventory studies in H2O-D2O mixtures with CEX as a probe have been made. Activation parameters and reaction constants have been evaluated. Oxidation products were identified by mass spectral analysis. An isokinetic relation was observed withβ = 378 K, indicating that enthalpy factors control the rate. The rate increases in the following order: CPD > CFL > CEX. The proposed mechanism and the derived rate law are consistent with the observed kinetics.

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