TITLE:
Kinetic and Mechanistic Study of Oxidation of Piperazines by Bromamine-T in Acidic Medium
AUTHORS:
Chandrashekar, B. M. Venkatesha, S. Ananda, Netkal M. Made Gowda
KEYWORDS:
Piperazines; Oxidation Kinetics; Mechanism; Bromamine-T; Buffer
JOURNAL NAME:
Modern Research in Catalysis,
Vol.2 No.4,
October
30,
2013
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.