Evaluation of some 5-pyrazolone-based copper(II) complexes as catalysts for the oxidation of trans-stilbene

The catalytic properties of the azo- and bisazo-5-pyrazolone-based three copper(II) complexes have been studied. Heating under reflux with or without ultrasonic irradiation was applied for the different equivalent amounts of three copper(II) catalysts (0.6 and 1.0 mol %) in ethyl acetate. It has been shown that all pyrazolone-based copper(II) complexes are active for catalytic oxidation of trans-stilbene in the presence of tert-butyl hydroperoxide as the oxidant, providing high selectivity and good conversion values. Heating was applied to the different solvents: chloroform, tetrahydrofuran, N,N-dimethylformamide, and dioxane. All catalysts can be safely used near to the boiling point of the oxidant without decomposition and the efficacy of ethyl acetate under conventional heating and heating-ultrasonic conditions has been determined. Heating-ultrasonic conditions and 1.0 mol % of catalysts gave higher conversion than conventional heating and 0.6 mol % of catalysts. A mechanism is proposed for the catalytic oxidation of trans-stilbene with tert-butyl hydroperoxide.