A kinetic study of the reaction between diaquooxalato(ethylenediamine) chromium(III) ion and concentrated hydrochloric acid

Abstract

This study of the reaction between diaquooxalato(ethylenediamine)chromium(III) ion and concentrated hydrochloric acid has shown that the product has the same spectrum as that of trans diaquodichloro(ethylenediamine)chromium(III) ion in concentrated hydrochloric acid. The kinetics indicate that the reaction takes place in two stages and that the rate law is, rate = ka HCl 2 where a HCl = activity of concentrated solutions of hydrochloric acid for both steps. This is interpreted as arising from a mechanism involving a pre-equilibrium followed by chloride insertion and a further equilibrium in which water in the Cr en Cl 2(H 2O) 2 + formed is replaced by chloride. The activation parameters were, for the first reaction ΔH‡ = 62.6 ± 10.6 kJ mol −1, ΔS† = −137.9 ± 0.6 JK −1 mol −1 and for the second reaction ΔH‡ = 94.1 ± 4.9 kJ mol −1 andΔS‡ = −68.0 ± 0.6 JK −1 mol −1.