KINETICS OF OXIDATION OF TETRACYANONICKELATE(II) BY CHLORINE MONOXIDE, CHLORINE, AND HYPOCHLOROUS ACID AND KINETICS OF CHLORINE MONOXIDE FORMATION

Oxidation of NiII(CN)4 2− by aqueous chlorine proceeds by three parallel pathways via Cl2O, Cl2, and HOCl to yield trans-{formula-omited}. The values of the second-order rate constants (M−1 s−1; 25.0 °C; μ = 0.10 M) for oxidations by Cl2O, Cl2, and HOCl are 1.3 × 107, 3.2 × 105, and 0.5, respectively. The proposed mechanism involves the formation of a nickel(IV) intermediate by Cl+ transfer to nickel(II) in the rate-determining step. This is followed by a rapid electron transfer between the nickel(IV) intermediate and NiII(CN)4 2− to give the final nickel(III) product. When the Cl2O path predominates and higher concentrations of NiII(CN)4 2− are used, the formation of Cl2O (catalyzed by acetic acid) becomes rate limiting: d[Cl2O]/dt = (k2 + k5[HOAc])[HOCl]2 where k2 is 0.12 M−1 s−1 and k5 is 280 M−2 s−1. Under these conditions the direct HOCl oxidation of NiII(CN)4 2− also contributes to the appearance of nickel(III). © 1990, American Chemical Society. All rights reserved.