Kinetic and Thermodynamic Studies of Uncatalysed and Hg(Ii)-Catalysed Solvolysis of a Chlorocobalt(Iii) Complex in Binary Aqueous Media

Abstract

The kinetics of solvolysis of trans — [Co(py)₄Cl₂]ClO₄ have been investigated in aquo-organic solvent media such as water + ethanol (0-60% v/v) and water -+ urea (0-40% w/w) in the temperature range 40-60°C. The first-order rate constant varies nonlinearly with the reciprocal of the relative permittivity ∊_r. The solvolysis of these types of complex involves a rate-determining dissociative step corresponding closely to 100% separation of Co³⁺ … Cl in the transition state. The Gibbs energy cycle relating the Gibbs energy of activation in water and in the mixtures to the Gibbs energies of transfer of individual ionic species between water and the mixtures ΔG°_t(Cl) can be applied. Moreover, more than one extrema in the enthalpies and entropies of activation are found with both binary aqueous solvent mixtures. The solvolysis of trans — [Co(py)₄Cl₂]ClO₄ has also been studied in the presence of Hg(II) and the ionic strength dependence of the reaction rate has been analysed.