Abstract: | The mechanism of the interaction of Cu+-α,α-dipyridyl complex (Cu+L2) with O2 in both neutral and acid media was studied by the stopped-flow method. The dependence of the mechanism on the acidity of the medium was established. In an acid medium H+ participated in a direct O2 reduction to HO2 by interaction with an oxygen adduct L2Cu+O2 formed without displacement of ligand molecules. In a neutral medium the reaction rate was limited by inner sphere charge transfer from Cu+ to O2 to form an oxygen “charge transfer” complex L2CuO+2. The latter interacted either with the second ion Cu+L2 or with the free ligand, or else it dissociated, reversibly or irreversibly, to form a radical anion O?2. The bimolecular rate constants of the oxygen “adduct” and “charge transfer” complex formation appeared to be kbi = (1.0 ± 0.1) × 105 and (1.5 ± 0.2) × 104M?1?sec?1, respectively. The effective termolecular rate constants of O2 reduction to HO2 in an acid medium (with contribution from H+) and to O?2 in a neutral medium (with contribution from α,α-dipyridyl) were kter = 2.7 × 108 and 107M?2?sec?1. The rate constants of the elementary steps were estimated. The auto-oxidation mechanism of the aquoion and complexes of Cu+ is discussed in terms of the results obtained. |