NONMETAL REDOX KINETICS - HYPOCHLORITE AND HYPOCHLOROUS ACID REACTIONS WITH CYANIDE

The rate expression for OCl- oxidation of CN- is -d[OCl-]/dt = (k1 + k2/[OH-])[CN-][OCl-], where k1 is 310 M-1 s-1 and k2 is 583 s-1 (25.0 °C, μ = 1.00 M). The observed inverse [OH-] dependence is due to the great reactivity of HOCl, which is 3.9 × 106 times more reactive than OCl- with CN-. The proposed mechanism with HOCl. is [formula omited] where k4 is 1.22 × 109 M-1 s-1, on the basis of pKa = 7.47 for HOCl at μ = 1.00 M, 25.0 °C. At high CN- concentration the HOCl reaction becomes so fast that proton-transfer reactions from H2O to OCl- and from HCN to OCl- [formula omited] contribute to the rate, where the values for and k-3 are 9 × 103 s-1 and 1.9 × 1010 M-1 s-1 and the values for k5 and k-5 are 2.2 × 107 M-1 s-1 and 6.6 × 108 M-1 s-1. Rate constants for Cl+ transfer from HOCl to nucleophiles decrease in value by 10 orders of magnitude with CN- ≥ SO32- > I- ≫ Br- ≫ Cl-, in accord with the decrease of anion nucleophilicity. © 1990, American Chemical Society. All rights reserved.