Selective photooxidation of cyclohexene with molecular oxygen sensitized by palladium phthalocyaninesulfonate

Photooxidation of cyclohexene by molecular oxygen was studied in an organic aqueous solution under visible light irradiation, using the title complex PdPcS and its analogues AlPcS and ZnPcS as sensitizer. The reaction gave cyclohexene hydroperoxide as the major product, and 2-cyclohexen-1-one and 2-cyclohexen-1-ol as the minor products. However, the product yield and selectivity, as well as the catalyst stability, were all greatly dependent on the sensitizer, organic solvent, and water concentration present in the mixed solution. Among the three sensitizers examined, PdPcS was the best in terms of both photoactivity and stability. The selectivity of cyclohexene hydroperoxide as high as 99% was obtained with PdPcS in a mixed solvent of CH3CN and H2O (85:15, v/v). Quenching experiments with sodium azide and benzoquinone showed that singlet oxygen was involved as the main reactive species responsible for the sensitized oxidation of cyclohexene.

The sensitized oxidation of cyclohexene by the title complex under visible light irradiation in an aerated aqueous solution of acetonitrile gave cyclohexene hydroperoxide as the major product with a selectivity as high as 99%. But the product yield and selectivity, as well as the catalyst stability were greatly dependent on the properties of the solvent used. Figure optionsDownload as PowerPoint slide