Enhancement of activity and selectivity in lipase-catalyzed transesterification in ionic liquids by the use of additives

BACKGROUND: Seven ionic liquids (ILs) based on 1-alkyl-3-methylimidazolium cation in combination with hexafluorophosphate and bis{(trifluoromethyl)sulfonyl}imide anions were tested as reaction media for lipase-catalyzed transesterification in low water conditions. With the aim of improving the activity and/or selectivity of the lipase, various treatments were applied to ionic liquid media such as equilibration with aqueous solutions of salts, NaHCO3 or Na2CO3, or the addition of a catalytic amount of a non-reactive organic base to the reaction mixture, triethylamine. RESULTS: The treated ionic liquids were shown to be excellent media for lipase-catalyzed ester synthesis by transesterification compared with conventional organic solvents, such as n-hexane. All treatments were found to enhance the synthetic activity of the enzyme, the best results being achieved with the addition of triethylamine. The addition of a catalytic amount of this base to the ILs resulted in a significant increase in both the synthetic activity and selectivity values. For instance, the synthetic activity in [emim+][TfN2-] was enhanced more than 12 times and the selectivity increased from 86% to 95% when triethylamine was used. CONCLUSION: These treatments could be easy-to-use approaches to improve the efficiency of enzymatic reactions in ionic liquids when the reaction does not proceed smoothly. (c) 2007 Society of Chemical Industry.