Abstract
Oxidations of piperazine, 1-methylpiperazine and 1-ethylpiperazine by bromamine-T (BAT) in buffered acidic medium have been kinetically studied at 303 K. The reaction shows a first-order dependence of the rate each on [BAT]0 and [piperazine]0, and an inverse fractional-order dependence on [H+]. The additions of halide ions and the reduction product of BAT, p-toluenesulfonamide, have no effect on the reaction rate. The variation of ionic strength of the solvent medium has no influence on the rate. Activation parameters have been evaluated from the Arrhenius and Eyring plots. A common mechanism consistent with the kinetic data has been proposed for all piperazines. The protonation constants of substrates have been evaluated. The Hammett linear free-energy relationship has been observed for the reaction with ρ = ?0.5 indicating that the electron-donating groups enhance the reaction rate by stabilizing the transition state. An isokinetic relationship observed shows β = 368 K indicating the dominance of enthalpy factors on the reaction rate.
Highlights
Piperazine is a heterocyclic nitrogenous compound [1] that has chemical similarity with piperidine as it has two opposing nitrogen atoms in the ring
The literature survey shows that the kinetic investigations of reactions of piperazines with iron (II) and cobalt (III) have been reported by Aravindakshan et al [9]
The oxidation kinetics of piperazines adds much to the knowledge of redox chemistry. These facts prompted us to undertake the study of kinetics of oxidation of piperazines by BAT in acidic buffer medium with a view to elucidate the reaction mechanism
Summary
Piperazine is a heterocyclic nitrogenous compound [1] that has chemical similarity with piperidine as it has two opposing nitrogen atoms in the ring. In animals, including man, piperazine and its salts are known to be highly effective as anthelmintics [2]. It is used in the treatment of gout and is an excellent solvent for uric acid [2,3]. Meager information exists in the literature on BAT-piperazines reactions [12,13,14,15]. The oxidation kinetics of piperazines adds much to the knowledge of redox chemistry. These facts prompted us to undertake the study of kinetics of oxidation of piperazines by BAT in acidic buffer medium with a view to elucidate the reaction mechanism
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