Kinetic studies on promazine oxidation by FeIII/CuII in acidic aqueous bromide solutions. Spectroscopic and kinetic non-additivity as evidence for the CuII–Br–FeIII-type heterobimetallic complex formation

摘要

The formation of CuII–Br–FeIII-type heterobimetallic complexes was observed spectrophotometrically, given the non-additivity of the spectra from the copper(II) and iron(III) complexes. The kinetics of the oxidation of promazine radical (ptz+?) to promazine 5-oxide, by iron(III) bromides, copper(II) bromides, and a mixture of these complexes in acidic aqueous solutions, have been studied using UV–Vis spectroscopy at I = 1.0 M (H+, Cu2+, Fe3+, Br?) and T = 318 K. Copper(II) inhibits the oxidation of the promazine radical to promazine sulfoxide using iron(III) complexes. A rate retardation effect, characterized by the dependence of the pseudo second-order rate constant (k II) on the copper(II) concentration k II = a/(1 + b[CuII]), can be rationalized as a result of CuII–Br–FeIII-type heterobimetallic complex formation.