Kinetics of the reactions of iodide with different forms of the µ-amido-µ-peroxo-bis{bis(ethylenediamine)cobalt(III)} complex

Abstract

Three forms of the µ-amido-µ-peroxo-bis{bis(ethylenediamine)cobalt(III)} complex are known to be present in the equilibrium (i) at hydrogen-ion concentrations 0·0025–0·05M. The kinetics of the reduction of these different [graphic omitted] forms with iodide (stoicheiometry two moles of iodide to one of complex) have been investigated. The product is the µ-amido-µ-hydroxo-complex (en)₂Co·µ(NH₂,OH)·Co(en)₂⁴⁺. With B the reaction is too slow for a detailed study. The reaction of AH is rapid and has to be studied by the stopped-flow method. The rate law is Rate =k_AH[AH][I^–], and at 2°k_AH= 5·83 (±0·11) l. mole^–1 sec.^–1. The rate law for the reaction of BH with iodide (0·025–0·20M) is of the form Rate =k_BH[BH][I]²+k₂[BH]. At 1°=k_BH= 2·65 (±0·11) l.² mole^–2 sec.^–1 and from data at two temperatures ΔH_BH‡=ca. 20 kcal. mole^–1 and ΔS_BH‡=ca. 17 e.u. The second term in this rate law, k₂[BH], is for the pathway in which isomerization, BH → AH, is rate-determining.