Reactions of co-ordinated nitriles. Part II. Nickel(II)- and cobalt(II)-promoted hydrolysis of 2-cyano-8-hydroxyquinoline

Abstract

Base hydrolysis of 2-cyano-8-hydroxyquinoline to the corresponding carboxamide has been studied spectrophotometrically; k_OH= 4·85 × 10^–3 l mol^–1 s^–1 at 45 °C and I= 1·0M. The hydrolysis is strongly promoted by nickel(II), cobalt(II), and copper(II). Thus the 1 : 1 complex of nickel(II) and 2-cyano-8-hydroxyquinoline undergoes base hydrolysis 2 × 10⁵ times faster than the uncomplexed substrate at 45 °C. Activation parameters for the uncatalysed base hydrolysis are ΔH‡= 13·4 ± 0·5 kcal mol^–1 and ΔS‡=–27 cal K^–1 mol^–1; corresponding values for the metal-promoted reactions are ΔH‡= 14·2 ± 0·5 kcal mol^–1, ΔS‡=–0·8 cal K^–1 mol^–1[nickel(II)] and ΔH‡= 14·3 ± 0·1 kcal mol^–1, ΔS‡=–3 cal K^–1 mol^–1[cobalt(II)]. The substantial rate acceleration is due to an entropy effect alone and possible mechanisms for the reaction are considered.