Dynamic Kinetic Resolution of Sec-Alcohols in Ionic Liquids/Supercritical Carbon Dioxide Biphasic Systems

Supercritical fluids and ionic liquids are neoteric solvents that can be used as non-conventional reaction media for enzymatic catalysis under optimised conditions. These solvents exhibit many different physical and chemical properties, but have two cross-points: they are not-miscible and can be easily separated from substrates and products, and they can be reused. As supercritical carbon dioxide (scCO2) can dissolve in the ionic liquid (IL) phase (up to 0.7 mole fraction), a new concept of biphasic bioreactors for Fine Chemicals syntheses may be developed by using both enzyme and chemical catalysts "immobilized" into the IL phase, and substrates transported by the scCO2 phase. The system was tested for the continuous chemoenzymatic dynamic kinetic resolution (DKR) of rac-1-phenylethanol in IL/scCO2 by using simultaneously immobilized lipase (Novozym 435) and acid zeolites catalysts at 50°C and 100 bars, providing good yields (up 98.0 %) for R-phenylethyl propionate ester with excellent enantioselectivity (up to 97.3 %), and without any activity loss after 14 days of operation.