Study of fast coupled reactions. The kinetics of formation of copper and zinc murexide

Abstract

The temperature-jump relaxation method has been used to study the rates of formation of the Cu²⁺ and Zn²⁺ murexide complexes in aqueous solution. Using the reaction scheme: [graphic omitted] where the formation of the encounter complex is considered as a pre-equilibrium stage and the elimination of water the rate-determining step, the following rate constants have been obtained: Cu²⁺/murexide, k₂=(k₁₂/k₂₁)k₂₃= 7 × 10⁷ l. mole^–1 sec^–1, k₃₂= 6.7 × 10³ sec^–1, Zn²⁺/murexide, k₂= 8 × 10⁶ l. mole^–1 sec^–1, k₃₂= 2 × 10⁴ sec^–1. These rate constants have been used to calculate the relaxation times of the coupled system, i.e., the mixture of zinc and copper murexide complexes. In all cases studied the experimentally observed relaxation times are in good agreement with those calculated.