Background: Biocatalysis has many attractive features in the context of green chemistry, due to the high efficiency of chemical transformations and the renewable character of the enzymes used. Since the beginning of this century, ILs have emerged as exceptionally interesting non-aqueous reaction media for biotransformations because of their unique solvent properties, headed by their negligible vapour pressure and their exceptional ability to maintain enzymes in active and stable conformations. However, the goal of green chemistry is much more than simply replacing hazardous solvents with environmentally benign ones, and it is necessary to devise new clean methodologies that will fulfil the sustainable requirements for efficient transformations of substrates, product recovery and the reuse of all the elements of the reaction system.
Results: The use biocatalyst in IL/scCO2 biphasic systems was the first approach forward to develop integral green chemical processes in non-aqueous environments. The combination of these sustainable tools provides synergies in both biocatalyst performance (i.e. improved activity and enantioselectivity, enhanced stability, etc.), and the genuine separation technologies of nearly pure products. Sponge-Like Ionic Liquids (SLILs) were recently reported as a new platform for green biocatalytic chemical processes using straightforward technologies. These SLILs are a new class of hydrophobic ILs based on cations with long alkyl side-chains (e.g. 1-octadecyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, ([C18mim][NTf2], etc.), which behaves as a sponge-like system by switching from liquid to solid phase as the temperature changes. Thus, such ILs are able to dissolve (“soak up”) hydrophobic compounds as a liquid phase, and products can then be “wrung out” by centrifugation of the resulting solid phase after cooling. Based on this property, clean biocatalytic processes for the production of nearly pure compounds of high added value (e.g. geranyl acetate, anisyl acetate, biodiesel, monolaurin, etc.) can be easily designed by the coupling of both biotransformation and separation steps, in a sustainable approach of high potential for practical applications at industrial level.
Conclusions: The use of biocatalytic approaches in green non-conventional reaction media holds much promise for the development of a sustainable chemical manufacturing industry. The combination of enzymes with multiphase neoteric systems (SLILs, ILs and/or scCO2) should be explored in the near future, as a clear strategy for developing integral new green multi-catalytic synthetic processes of industrial interest (e.g. pharmaceutical drugs).