Kinetic Study of the Oxidation of Catechol by Aqueous Copper(II)

The kinetics of the oxidation of catechol by aqueous copper(II) have been studied as a function of reactant concentrations at pH 6.4−7.2. To follow the reaction, a spectrophotometric method has been developed that circumvents the problem of precipitation of decomposition products of the initial o-quinone oxidation product. The rate law shows that the reactive species is the monocatecholate complex of CuII, and that this species undergoes rate-limiting intramolecular electron transfer with k = 1.9 × 10-5 s-1 (22 ± 1 °C, μ = 0.125 M NaClO4). The results have allowed a reanalysis of previous work on the autoxidation in the aqueous CuII−catechol−dioxygen system, and comparisons to mechanisms of copper(II) oxidases.