Development of environmentally friendly lipase-catalysed kinetic resolution of (R,S)-1-phenylethyl acetate using aqueous natural deep eutectic solvents

Abstract

Over the past decade, natural deep eutectic solvents (NADES) have become promising green solvent from both environmental and technological perspectives. The number of structural combinations encompassed by NADES is tremendous; thus, NADES with unique physicochemical properties can be designed for a particular purpose, such as for efficient biocatalytic processes. The aim of this work was to prepare several NADES based on renewable sources (biomass energy) and to apply these solvents in the industrially interesting process of lipase-catalysed (R)-1-phenylethanol synthesis. Based on experimental data on lipase behaviour in the tested NADES, choline chloride:glycerol (ChGly) was selected as the most promising solvent for the given reaction. The resulting (R)-1-phenylethanol was also successfully isolated and purified from the reaction mixture using liquid-liquid extraction with ethyl acetate, whilst ChGly was recycled and reused. (R)-1-phenylethanol and unreacted (S)-1-phenylethyl acetate were purified on silica gel columns with yields of 81.91 %. The biocatalyst was also successfully recycled and reused in 4 cycles. Based on laboratory-scale optimum conditions, (R)-1-phenylethanol synthesis performed in a 500 mL batch reactor achieved reaction conversions comparable to those obtained with millilitre-scale biocatalytic reactions. The downstream process was also performed on a preparative scale with a yield of 49.48 %.