Water as Cosolvent: Nonviscous Deep Eutectic Solvents for Efficient Lipase-Catalyzed Esterifications

The use of deep eutectic solvent (DES)/water mixtures were explored for the selective enzymatic synthesis of alpha-monobenzoate glycerol (alpha-MBG) from glycerol and benzoic acid as substrates. Experiments were performed with four DES, three of them containing choline chloride (ChCl), combined with urea (URA), glycerol (GLY), and ethylene glycol (ETA) (in all cases ChCl/HBD 1:2 mol ratio), and another one formed with methylammonium chloride and glycerol (MA/GLY 1:3 mol ratio). The best conversions (99%) were achieved with immobilized lipase B from Candida antarctica (CAL-B) when ChCl/GLY was used as the solvent and the substrate at the same time. The use of water as a cosolvent (8% v/v) led to a significant decrease in the viscosity of the DES, and full conversions were then reached. Reusability studies of the biocatalyst revealed a 37% decrease in activity after the first batch, but the activity remained mostly constant for the rest of the cycles.