Sponge-like ionic liquids: a new platform for green biocatalytic chemical processes

Abstract

To build a green chemical industry it is necessary to develop integrated processes of selective transformation and separation capable of directly providing pure products, including the reuse of all the elements of the reaction system, e.g. catalysts, solvents, etc. In recent years, the unsurpassed selectivity of enzymes for chemical reactions, combined with the excellent solvent properties of ionic liquids (ILs), has provided an excellent setting for carrying out sustainable chemical transformations. However, implementation of this to industrial chemical processes needs the development of straightforward, cheap and/or sustainable approaches for pure product extraction, including the reuse of ILs. Hydrophobic ILs based on cations with long alkyl side-chains, e.g. octadecyldecyltrimethylammonium bis(trifluoromethylsulfonyl)imide, ([C₁₈tma][NTf₂]), are temperature switchable ionic liquid/solid phases that behave as sponge-like systems (Sponge-Like Ionic Liquids, SLILs). Based on this newly found property, SLILs have been used to develop straightforward and clean approaches for producing nearly pure synthetic liquid compounds of high added value (e.g. flavour esters, biodiesel, etc.) in two steps: a biocatalytic step that occurs as monophasic liquid systems, followed by a product separation step carried out by cooling/centrifugation/filtration of the solid reaction system. SLILs therefore might be considered a new green platform for easy preparation of pure products.