Oxidative Coupling of Phenols Catalyzed by Copper Chloride Coordinated to Aminated Polystyrene:A Possible Model Reaction for Dioxygen Reduction by Laccase and Tyrosinase

The influence of ZnCl2 on the reaction rate of the oxidative coupling of 2,6-disubstituted phenols, catalyzed by Cu-polyamine complexes has been investigated. It is shown that the role of free CuCl2, previously shown to be essential for catalytic activity, can be taken over by ZnCl2. Furthermore, the influence of the dioxygen pressure on the reaction has been investigated. The reaction rate at high phenol concentrations appears to be dependent on the dioxygen concentration, the type of phenol and the degree of substitution of dimethylaminomethylated polystyrene. Therefore it can be concluded that the reaction is not controlled by diffusion of dioxygen into the liquid reaction medium. The results are discussed in terms of mechanisms published by other authors in which dimeric copper species act as catalytic centers. A mechanism for the reduction of dioxygen by the copper complexes is suggested and its relation to the Type-3 Cu of laccase and the Cu-pair of tyrosinase is discussed