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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

1980; Oxford University Press; Volume: 53; Issue: 9 Linguagem: Inglês

10.1246/bcsj.53.2437

1348-0634

Seiji Yoshimura, Akira Katagiri, Yasuo Deguchi, Shiro Yoshizawa,

Inorganic and Organometallic Chemistry

Abstract The kinetics and mechanism of the decomposition of the tetracyanocuprate(II) ion (CuII(CN)42−) 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 CuII(CN)42−, 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 CuII(CN)42− is derived; v=k0[CuII(CN)42−]2⁄[CN−]2, where k0 is calculated to be 74 mol·dm−3·s−1 at 25 °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 CuII(CN)3−, followed by the rate-determining bimo-lecular reaction of CuII(CN)3− to give 2CuI(CN)2−+(CN)2 (Mechanism A), and the formation of a binuclear complex, CuII2(CN)62−, followed by the rate-determining decomposition of CuII2(CN)62− to give 2CuI(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.