Studies of the Anodic Oxidation of the Cyanide Ion in the Presence of the Copper Ion. IV. The Kinetics and Mechanism of the Decomposition of the Intermediate Tetracyanocuprate(II) Ion

Article abstract of DOI:10.1246/bcsj.53.2437

The kinetics and mechanism of the decomposition of the tetracyanocuprate(II) ion (Cu^II(CN)4^2-) have been investigated by ESR measurements.Aqueous solutions of potassium cyanide with a small amount of copper(I) cyanide were electrolyzed in a cell the platinum anode of which was set in the resonant cavity of an ESR spectrometer.Since Cu^II(CN)4^2-, which is formed as an intermediate, gives a definite ESR spectrum, its concentration in the anode compartment is estimated from the intensity of the first-derivative spectrum at a fixed magnetic field.From the decay curves of the ESR intensity after the steady-state electrolysis currents have been switched off, a rate equation for the decomposition of Cu^II(CN)4^2- is derived; v = k₀II(CN)4^2->²/->², where k₀ is calculated to be 74 mol*dm^-3*s^-1 at 25 deg C.This rate equation is also confirmed by ESR measurements during steady-state electrolysis, where the value of k₀ = 60 mol*dm^-3*s^-1 is obtained.On the basis of the kinetics, two possible mechanisms are proposed: the formation of Cu^II(CN)3^-, followed by the rate-determining bimolecular reaction of Cu^II(CN)3^- to give 2Cu^I(CN)2^- + (CN)2 (Mechanism A), and the formation of a binuclear complex, Cu^II2(CN)6^2-, followed by the rate-determining decomposition of Cu^II2(CN)6^2- to give 2Cu^I(CN)2^- + (CN)2 (Mechanism B).The kinetics and the mechanism are compared with those of the chemical reaction between the copper(II) ion and the cyanide ion.