Enzymatic reactions often show excellent selectivity, and, in the case of chiral synthesis, excellent enantioselectivity. The natural solvent of enzymatic reactions is water. However, some reactions run very slowly in watery media. The reasons are mainly mass transfer limitations, are derived from reaction kinetics, or solvent-induced direction change of the reaction. Generally, acylation/ester formation reactions are catalyzed by lipases better in nonpolar solvents while hydrolysis is preferred in water. Although a large number of enzymatic reactions perform fast and selectively in organic solvents (or somewhat lower but even selectively at neat conditions), the separation of the solvent, remaining substrate and product is problemtic and limits the industrial applicability of these methods.
Some enzymes, mainly lipases, are active in supercritical carbon dioxide (scCO2). Enzymatic reactions in scCO2 , the most widely studied reactions are lipase catalysed acylation reactions, do not only have a well-known temperature optimum, but the enzyme activity is also dependent on the applied pressure . Obiviously, increasing the molar ratio of the acetate donor also enhances the reaction rate. In most cases vinyl acetate, isopropenil acetate or butyl acetate are applied.
In the recent years we investigated enzyme catalysed kinetic resolutions in batch, circulated and continuous supercritical reactors, and a systematic development approach was also suggested. The reactions studied were mainly acylation reactions, but also a lactame ring opening reaction was investigated and coupled with extraction based product-substrate separation.
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