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 Cu(II), and that this species undergoes rate-limiting intramolecular electron transfer with k = 1.9 x 10(-5) s(-1) (22 +/- 1 degrees C, mu = 0.125 M NaClO(4)). The results have allowed a reanalysis of previous work on the autoxidation in the aqueous Cu(II)-catechol-dioxygen system, and comparisons to mechanisms of copper(II) oxidases.