Metal-catalysed ionization of a cyclic 1,3-diketone. The effects of nickel(II) and copper(II) on the lonization of 2-acetylcyclohexanone

Abstract

The kinetics and mechanisms of the reactions of nickel(II) and copper(II) with 2-acetylcyclohexanone to form metal–enolate complexes have been investigated in methanol–water solution (70 : 30 v/v) at 25 °C and ionic strength 0.5 mol dm^–3. A mechanism is proposed which accounts satisfactorily for the kinetic data. Nickel(II) reacts exclusively with the enol tautomer of the ligand with a rate constant of 0.114 dm³ mol^–1 s^–1 Copper(II) reacts with both the keto and enol tautomers of the ligand with rate constants of 0.929 and 1.27 × 10³ dm³ mol^–1 s^–1, respectively. The catalytic effect of both Ni²⁺ and Cu²⁺ on the ionization rate constants of the keto and enol tautomers of the ligand have been calculated.