Clean enzymatic production of flavor esters in Spongelike Ionic Liquids

The biocatalytic synthesis of 16 flavor esters was carried out by the direct esterification of aliphatic acids (e.g., acetic, propionic, etc.) with an alcohol (e.g., cinnamyl alcohol, benzyl alcohol, anisyl alcohol, rac-1-phenylethanol, or rac-sulcatol) using hydrophobic ionic liquids (ILs) based on ammonium or imidazolium cations containing a long alkyl side chain (e.g., hexadecyltrimethylammonium bistriflimide, [C16tma][NTf2]) as the reaction medium. As temperature-switchable liquid/solid phases, these ILs behave as spongelike systems (so-called spongelike ionic liquids (SLILs)), which act as excellent monophasic reaction media for the lipase-catalyzed synthesis of flavor esters. Under appropriate selected reaction conditions (e.g., enzyme, substrate molar ratio, nature of the SLIL, etc.), product yields near 100% were obtained for all of the synthesized flavor esters. Because of the unique spongelike properties of these ILs, a separation protocol based on the centrifugation of the solid IL/flavor ester...