Abstract
Oxidation of [Ni(cyclam)]2+, cyclam= 1,4,8,11-tetraazacyclotetradecane, accelerated by sulfur dioxide, was studied spectrophotometrically by following the formation of [Ni(cyclam)]3+ under the conditions: [Ni(cyclam)]2+ = 6.0 × 10-3M; initial [Ni(cyclam)]3+= 8.0 × KT6 M: [cyclam] = 6.0 × 10-3M; [SO2] = (1.0–5.0) × 10-4M and 1.0 M perchloric acid in oxygen saturated solutions at 25.0°C and ionic strength = 1.0 M. The oxidation reaction exhibits auto-catalytic behavior in which the induction period depends on the initial Ni(III) concentration. A kinetic study of the reduction of Ni(III) by SO2 under anaerobic conditions, and the oxidation of Ni(II), showed that the rate-determining step involves reduction of Ni(IIl) by SO2 to produce the SO3- radical, which rapidly reacts with dissolved oxygen to produce SO5 -and rapidly oxidizes Ni(II). The results clearly show a redox cycling process which depends on the balance of SO2 and oxygen concentrations in solution.
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