An electrochemical investigation of the interaction between the superoxide ion and cations of group 2a in aqueous solutions

The reduction of molecular oxygen in aqueous solutions containing triphenylphosphine oxide and a cation of Group 2a at a dropping mercury electrode has been studied by polarography and cyclic voltammetry. It was found that the superoxide ion, generated by monoelectronic reduction of molecular oxygen, gave rise, in the presence of a Group 2a cation, to a new wave whose E 1 2 value shifts towards less negative potential values at increasing cation concentrations. This effect was the most pronounced with Ca2+. Analysis of the reduction wave supports the hypothesis of the generation, at the electrode-solution interface, of a complex involving the superoxide and the metal cations in the stoichiometric ratio 1:1. The overall electrochemical process can be characterized by two irreversible charge transfers and, in the vicinity of the electrode-solution interface, by two concomitant parallel chemical reactions (sponta- neous dismutation of the superoxide ion and interaction between the superoxide and the Group 2a cations). © 1988.