Continuous Flow Enzymatic Kinetic Resolution and Enantiomer Separation using Ionic Liquid/Supercritical Carbon Dioxide Media

Abstract

AbstractThe combination of kinetic resolution in ionic liquids (IL) and selective extraction with supercritical carbon dioxide (scCO2) provides a new approach for the separation of enantiomers as exemplified by the lipase‐catalyzed esterification of chiral secondary alcohols. Excellent enantioselectivities are achieved upon conversion of alcohols 1a–e to the corresponding acetates 4a–e or laureates 5a–e using various modifications of the lipase from Candida antarctica (CaL‐B) in imidazolium‐based ionic liquids. The anion of the ionic liquid has a significant influence on the performance of the bio‐catalyst with bis(trifluoromethanesulfonamide) [BTA] giving the best results. The acetates 4a–e can be extracted from the reaction mixture preferentially over the alcohols 1a–e with scCO2 under certain conditions, but preparatively useful selectivities would require advanced multi‐step extraction procedures. In contrast, efficient separation is possible with relatively simple equipment if alcohols 1a–e are extracted preferentially from their corresponding laureates 5a–e. A “green” continuous process for the resolution of racemic alcohols without the use of organic solvents was devised on the basis of these findings.