Kinetics of oxidation of hydrogen azide (hydrazoic acid) by tris(2,2′-bipyridine)nickel(III) ions in aqueous perchlorate media: comparison with oxidation by aqua-cations

Abstract

E.s.r. measurements on solutions of Ni^II containing 2,2′-bipyridine (bipy) confirm that anodic oxidation produces Ni^III. The stoicheiometry and kinetics of oxidation of HN₃ by [Ni(bipy)₃]³⁺ have been investigated. Unlike the oxidations of H₂O₂ and Br^– by this cation, with HN₃ the rate varies with the concentration of HClO₄ at constant ionic strength. Under conditions where specific cation effects are eliminated, the rate is directly proportional to [H⁺]^–1, suggesting that the kinetically active entity of the hydrazoic acid is N₃^–. No removal of bipy from the Ni^III occurs before the slow oxidative step, even though an outer-sphere intermediate complex may be formed between [Ni(bipy)₃]³⁺ and N₃^–. This system is compared with the oxidations of HN₃ by aqua-cations and with the oxidations of other ligands by [Ni(bipy)₃]³⁺.