Kinetics and enantioselectivity of lipase-catalyzed reactions in SCCO2

The use of enzymes acting as catalysts in nonaqueous media has been frequently described in the scientific literature. As a matter of fact many organic media exhibit advantages as stabilization of enzyme, dissolution of hydrophobic compounds and the possibility of shifting thermodinamic equilibrium towards the synthesis of esters and amides. Very recently attention has also been devoted to the utilization of different fluids in supercritical conditions. Supercritical fluids exhibit properites similar to organic solvents with additional capacities of enhancing transport phenomena and facilitating post reactional separation which makes them more attractive. The present communication reports the results and some general observations on parameters which enhance the reactivity and the enantiomeric eccess in lipase catalysed reactions in supercritical CO2. We examined the lipase catalysed synthesis of some esters from secondary alcohols and acetic anhydride, as a function of pressure, temperature, substrates concentration, and we compared the performance of the enzyme with the corresponding reactins in aliphatic and aromatic solvents.