Synthesis of glycidyl esters catalyzed by lipases in ionic liquids and supercritical carbon dioxide

Free and immobilized commercial lipases from Candida antarctica (CALA and CALB) and Mucor miehei (MML) were assayed as catalysts in the synthesis of glycidyl esters from rac-glycidol in non-aqueous conditions. Four different ionic liquids (ILs), based on dialkylimidazolium or quaternary ammonium cations associated with hexafluorophosphate or bis(trifluoromethane)sulfonyl amide anions, and supercritical carbon dioxide (40-50 degreesC and 100-150 bar) were used as reaction media. All lipases were able to catalyze glycidyl ester synthesis. Also, their activity was greatly enhanced (up 95-times) by both the use of ILs media in comparison with a classical organic solvent (toluene), and the increase in the alkyl chain length of the acyl donor ester. The activity and enantioselectivity exhibited by each lipase were practically independent of the assayed ILs. R-Glycidyl esters were preferentially obtained by both CALA and MML biocatalysts, while S-glycidyl ester synthesis was favoured by CALB, which showed the highest degree of activity in all cases. Continuous processes for glycidyl butyrate synthesis in supercritical carbon dioxide, catalyzed by each assayed lipase (free and immobilized) suspended in 1-ethyl-3-methylimidazolium bis[(trifluoromethyl) sulfonyl]amide, were also studied leading to excellent results. Supercritical CO2/IL biphasic systems slightly reduced the synthetic activity of lipases, while the enantioselectivity of the process remained unchanged. (C) 2004 Elsevier B.V. All rights reserved.