Bromite ion catalysis of the disproportionation of chlorine dioxide with nucleophile assistance of electron-transfer reactions between ClO(2) and BrO(2) in basic solution.

The rate of ClO(2) conversion to ClO(2)(-) and ClO(3)(-) is accelerated by BrO(2)(-), repressed by ClO(2)(-), and greatly assisted by many nucleophiles (Br(-) > PO(4)(3-) > HPO(4)(2-) > CO(3)(2-) > Cl(-) approximately OH(-) > CH(3)COO(-) approximately SO(4)(2-) approximately C(5)H(5)N >> H(2)O). The kinetics (at p[H(+)] = 9.3-12.9) show that the first step of the mechanism is an electron transfer between ClO(2) and BrO(2)(-) (k(1) = 36 M(-1) s(-1)) to give ClO(2)(-) and BrO(2). This highly reversible reaction (k(1)/k(-1) = 1 x 10(-6)) accounts for the observed inhibition by ClO(2)(-). The second step is an electron transfer between ClO(2) and BrO(2) to regenerate BrO(2)(-) and form ClO(3)(-). A novel aspect of the second step is the large kinetic contribution from nucleophiles (k(Nu)) that assist the electron transfer between ClO(2) and BrO(2). The k(Nu) (M(-2) s(-1)) values at 25.0 degrees C vary from 2.89 x 10(8) for Br(-) to 2.0 x 10(4) for H(2)O.