Oxidative coupling of 2,6-dimethylphenol catalyzed by copper(II) complexes in aqueous solution

摘要

The oxidative coupling reaction of 2,6-dimethylphenol (DMP) with H _2O_2 catalyzed by four copper(II) complexes was investigated in Tris-HNO_3 buffer solution at 25°C. The kinetics of formation of diphenoquinone (DPQ, 4-(3,5-dimethyl-4-oxo-2,5- cyclohexadienylidene)-2,6-dimethyl-2,5-cyclohexadienone) from DMP was studied in detail. The kinetic parameters k_2 and K_m were obtained in the pH range of 6.0-9.0. The copper(II) complexes exhibited the optimal catalytic activity at around pH 7.0. The pH effect was reasonably explicated by the catalytic kinetic model suggested in this work. The catalytic mechanism was discussed. The deprotonized associated radical LCu~I(OH ~-)-~?OOH was suggested as the possible predominant species to oxidize DMP. The CAC and CAO coupling products were analyzed and the ratio of poly (2,6-dimethyl-1,4-phenylene ether) (PPE) to DPQ was also evaluated. Both in weak acidic (pH < 6.5) and in alkaline aqueous solution (pH > 8) were suitable to the CAO coupling reaction in our catalytic systems.