Adalagere Somashekar Manjunatha

Oxidative conversion of anilines to azobenzenes with alkaline chloramine-T

Anilines are widely used in the manufacture of dyes, medicinals, plastics and perfumes. Anilines are readily oxidized to give products depending on reaction conditions. Conversion of anilines to azobenzene is important in organic synthesis. In the course of this research, optimum conditions for the facile oxidative conversion of anilines to azobenzenes have been established in very good yields. The kinetics of oxidation of aniline, p-methoxyaniline, p-methylaniline, p-carboxylicaniline and p-nitroaniline by chloramine-T (CAT) in NaOH medium shows identical kinetics with a first-order dependence of rate on [CAT]o, fractional-order on [Aniline]o, and an inverse-fractional order on [OH-]. Activation parameters and decomposition constants have been determined. Oxidation products were characterized by NMR spectral studies. Isokinetic temperature is 415 K indicating enthalpy as a controlling factor. The rates increased in the order: p-methoxyaniline>p-methylaniline>aniline>p-carboxylicani- line>p-nitroaniline. A Hammett linear free energy relationship is observed for the reaction with ρ=-0.52. Reaction scheme and kinetic rate law were deduced. We have developed a simple and efficient protocol for the synthesis of azobenzenes by anilines in good yields and hence we believe that this methodology will be a valuable addition to the existing methods.

Oxidative Cleavage of β-Lactam Ring of Cephalosporins with Chloramine-T in Alkaline Medium: A Kinetic, Mechanistic, and Reactivity Study

Cephalosporins are β-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]o and [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 with β = 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.