The kinetic study on lipase-catalyzed transesterification of α-cyano-3-phenoxybenzyl alcohol in organic media

Optically active form of α-cyano-3-phenoxybenzyl alcohol (CPBA), building block of pyrethroid insecticides, was synthesized as its acetate by the combination of anion-exchange resin-catalyzed transcyanation between m-phenoxybenzaldehyde and acetone cyanohydrin, and lipase-catalyzed enantioselective transesterification of the resulting cyanohydrin with vinyl acetate. Through a screening of enzymes, Alcaligenes sp. lipase showed the highest activity and the conversion exceeded 50%. Effects of solvents and temperatures on this reaction were studied. Among four kinds of solvent, diisopropyl ether was a best choice. The optimal temperature was 50 °C. Although the external diffusion limitation could be excluded by raising the rotational speed, internal diffusion could not be ignored, since the enzyme was an immobilized one on the particles with a considerably large diameter. The e.e. values of CPBA ester were measured by polarimeter and NMR.