Application Of Mesoporous Silica In The Synthesis Of Chiral ?-phenylethanol By Asymmetric Transfer Hydrogenation

Inorganic mesoporous silica has regular spherical structure,slits pore structure and better stability,which is good to use as support and microcapsule reactor.Chiral a-phenylethanol can be widely applied in medicine,spices,organic synthesis etc.as the precursor and intermediate in the synthesis of many complex chiral compounds for its simple structures.Asymmetric Transfer Hydrogenation of acetophenone is one of the common methods to obtain the enantiomeric ally pure chiral a-phenylethanol.The mesoporous silica microspheres were synthesized by polymerization induced colloid aggregation?PICA?.By adding different additives to modification mesoporous silica microspheres,suitable support for catalytic reaction was selected.Chitosan chiral ligand and reactive metal were immobilized in mesoporous silica support to gain heterogeneous catalysts,which were used in asymmetric transfer hydrogenation.Capsulated rhodium catalyst,which was synthesized in the mesoporous silica microcapsule reactor through the "ship-in-a-bottle"method,was prepared for the asymmetric transfer hydrogenation of acetophenone.The structure of immobilized catalysts and microcapsule reactor was characterized through isothermal nitrogen adsorption/desorption.XRD,FT-IR and TEM.The mesoporous silica microsphere synthesized by polymerization-induced colloid aggregation modified by SDBS has good spherical dispersion,uniform grain size and stable structure.SiO₂ is great support immobilized active metal,at the same time,SiO₂ can be microcapsule reactor capsuled homogeneous catalyst.The characterization results of SiO₂-CS-M showed that the structure of the silica kept the microsphere structure after immobilization.But the structure of the microspheres broke after impregnation and support with large pore size and low surface area leaded to more agglomeration of reactive metal.And the result of reaction influenced by different reactive metal.SiO₂-CS-Pt and SiO₂-CS-Rh have good catalytic activity.The best reaction conditions of asymmetric transfer hydrogenation is reaction temperature 40?.reaction time 4h and 0.2mL acetophenone.The conversion of acetophenone on SiO₂-CS-Rh is 50.7%,and the ee of R-a-phenylethanol on SiO₂-CS-Pt is 44.6%.The homogeneous rhodium catalyst was capsulated in mesoporous silica microcapsule reactor through "ship-in-a-bottle".The characterization results show that there is no bond between catalyst and reactor.The bore diameter of microcapsule reactor decreased and there is no change in the mesoporous structure.The conversion of acetophenone is 52.4%,and the ee of R-?-phenylethanol is 95.5%under 60? reaction temperature and 6h reaction time.The result of mesoporous silica microcapsule reactor encapsulated with homogeneous rhodium catalyst has great catalytic performance and can be recycled with no apparent loss of activity,which is conformed to the requirements of green chemistry.