Inner sphere oxidation of N,N′-ethylenebis(isonitrosoacetyleacetoneimine)copper(II) by N-bromosuccinimide in aqueous weakly acidic solutions

Abstract

The kinetics of oxidation of N,N'-ethylenebis(isonitrosoacetyleacetoneimine) copper(II) complex, CuL, by N-bromosuccinimide (SBr) in weakly aqueous acidic solutions was studied under pseudo-first-order conditions. Plots of In (AA) versus time where A and A are absorbance values of the Cu(III) product at time t and infinity, respectively, showed marked deviations from linearity. The curves showed an acceleration of reaction rate consistent with an autocatalytic behavior. In the presence of Hg(II) ions, plots of In(Aco 00 - A) versus time are linear up to >85% of reaction. The value of the observed rate constant, k obs, increases with decreasing pH. At constant reaction conditions, the dependence of the observed rate constants, k obs, is described by Eq. (1). kobs = ko + k1 [H+] The dependence of both kand k 1 on [SBr] is not linear. The mechanism of the title reaction is consistent with an inner sphere mechanism in which a pre-equilibrium step precedes the electron transfer step. The overall rate law is represented by Eq. (2) where [CuIL]t and K 1 represent the total copper(II) complex concentration and the pre- equilibrium formation constant, respectively. d [CuL+]/dt = {(ko+k₁ [H+]) [SBr] [CuL]}/(1 + K₁ [SBr])