Effect of fumarate on the kinetics and reaction mechanism of Cu⁺_aq with dioxygen

The kinetics of the reactions: Cu⁺_aq + O₂ ⇄ (CuO₂)⁺_aq and (CuO₂)⁺ + Cu⁺_aq →^H+ 2Cu²⁺_aq + H₂O₂ were studied applying the pulse radiolysis technique, Kk = (2.3 ± 0.4) × 10⁸ dm⁶ s^-1 mol^-2, in good agreement with the value calculated from literature data. The complex Cu^I(fum) (fum = fumarate) reacts considerably slower than Cu⁺_aq with dioxygen so that the rate law reflects only the reaction of Cu⁺_aq. A comparison of the results with those reported for the ligands L (water, CH₃CN, phenanthroline, bipyridine or fumarate) indicates that the ligand affects the stability constant of the Cu^IL·O₂ complex, and for fumarate also the subsequent reaction.