Kinetics of the reaction of aquocobalt(III) ions with hydrazoic acid in perchlorate media

Abstract

The rapid reaction of Co^III with hydrazoic acid has been investigated at high initial ratios [HN₃]/[Co^III] using the stopped-flow technique. The rate is proportional to [Co^III][HN₃]² and is independent of acidity in the region 0·5–5·0M-HClO₄. This is contrasted with the slower reaction at low initial ratios [HN₃]/[Co^III]. This system is compared with other cation–HN₃ systems, and it is concluded that intermediate hydrazido-complexes are involved in the reaction. The kinetics of the Co^III+ HN₃ reaction and other redox reactions of Co^III are consistent with a hydrolysis equilibrium constant for Co^III_aq of K_hca. 10^–2–10^–3 mole l.^–1, and the kinetics of substitution reactions of Co^III_aq are not inconsistent with this value for K_h. The mechanism of the Co^III+ HN₃ reaction is discussed in terms of possible dimeric species of Co^III_aq.