Synthesis of Macroporous Hollow Silica Using Zeolites as Cores and Their Application as Spports for Enantioselective Reaction

초록

Recent research trend in catalysis is to develop methodology to allow the recovery and reuse of the catalyst, because of expensive cost of some catalysts. One such method is to synthesize the macroporous materials with large pore size and uniform pore size distribution. Then homogeneous catalysts are immobilized in the macroporous inorganic supports that making it possible to perform the reaction heterogeneously.4-5 In this regard, this study focuses on the development of new chiral metal complexes and the application as catalysts in asymmetric reactions. It acts as highly enantioselective catalyst for the asymmetric hydrolysis of terminal epoxides.1-3 In this report, the method of reusable chiral salen-metal complexes catalyst is explained. It is using a NaY zeolite as a template core. After removal of he NaY cores by hydrochloric acid, chiral Co(III) salen complexes were immobilized in the vacant cores through encapsulation treatment. In addition, the new method to fabricate the hollow type inorganic support is by using microporous zeolites, such as LTA, FAU and ANA. In this work the metal containing chiral salenes were incorporated into the macropores of hollow zeolites. Typically, zeolites were coated by TEOS/C18 silanes through hydrolysis in basic aqueous solution. After calcination, to remove C18 silanes, the chiral salenes were impregnated, and the additional silica layer were coated to entrap those complexes. The activities of heterogeneous chiral salen catalysts were examined in the hydrolytic kinetic resolution (HKR) of epichlorohydrin (ECH). The conversion and ee% values were determined by capillary GC equipped with chiral columns. (CHIRALDEX [G-TA, 20 m × 0.32 mm i.d., Astech, USA). The macroporous hollow silica could be fabricated so easily by sacrificial method using NaA, and the samples obtained in this work was efficient support for immobilization of chiral Co(III) salen complexes.