Chiral Heterogeneous Catalyst of Pd-chitosan Supported on SiO_2 for Transfer Hydrogenation of Acetophenone

The natural biopolymer of chitosan was supported on the surface of silicon dioxide, and then palladium was coordinated on it, to prepare the palladium-chitosan-silica complex (Pd-CS-SiO_2)chiral heterogeneous catalyst. The asymmetric transfer hydrogenation of acetophenone to R(S)-1-phenyl ethanol in atmosphere with 2-propanol as H-donor and solvent was studied as a model reaction. The effects of the Pd loading, reaction temperature, reaction time, and promoter of base on the performance of the catalyst were investigated. The results indicate that the Pd-CS-SiO_2 catalyst has a good catalytic activity and selectivity to the product for the asymmetric hydrogen transfer reduction of acetophenone. The addition of NaOH can increase the reaction rate and conversion of acetophenone significantly. The conversion of acetophenone increases with an increase of the Pd loading, but the enantiomeric excesses of 1-phenyl ethanol is higher at lower Pd loading. After reaction at 80 ℃ for 24 h, the conversion of acetophenone is 100% with 98% selectivity to 1-phenyl ethanol. At 30 ℃, the enantiomeric excess of R-1-phenyl ethanol reaches to 13.7%.