A Continuous Reactor for the (Chemo)enzymatic Dynamic Kinetic Resolution of Rac-1-Phenylethanol in Ionic Liquid/Supercritical Carbon Dioxide Biphasic Systems

Enzymatic transformations in ionic liquids (ILs)/supercritical carbon dioxide (scCO2) biphasic systems, whereby enzyme molecules are ``immobilized" in the IL phase and substrates/products are transported by the scCO2 phase, are described as a way for carrying out clean synthetic chemical processes to produce pure products. As a model system to study, the ionic liquid butyltrimethyl ammonium (bis(trifluoromethane)sulfonyl imine) ([btma][NTf2]) was assayed for Candida antarctica lipase B (CALB)-catalyzed the kinetic resolution of rac-1-phenylethanol. The suitability of this IL was established from both the activity and stability of the enzyme. A continuous dynamic kinetic resolution (DKR) process in [btma][NTf2])/scCO2 biphasic system was carried out by using simultaneously both immobilized Candida antarctica lipase B in silica gel and silica modified with benzenosulfonic acid groups (SCX) catalysts at 50 ºC and 10 MPa, providing a good yield (78 %) for (R)-1-phenylethyl propionate product with excellent enantioselectivity (ee = 92 %) in continuous operation.