Abstract
The kinetics of oxidation of N,N'-ethylenebis(isonitrosoacetyleacetoneimine) copperII) complex, (CuL)-L-II, by N-bromosuccinimide (SBr) in weakly aqueous acidic solutions was studied under pseudo-first-order conditions. Plots of ln(A(infinity) - A(t)) versus time where A(t) and A(infinity) 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 HgII) ions, plots of ln(A(infinity) - A(t)) 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).
k(obs) = k(o) + k(1)[H+] (1)
The depen dence of both k(o) and 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 [(CuL)-L-II](t) and K-1 represent the total copper(II) complex concentration and the pre-equilibrium formation constant, respectively.
d[(CuL+)-L-III]/dt = {(k(o) + k(1)[H+])[SBr][(CuL)-L-II](t)}/(1 + K-1[SBr]) (2)