Diffusion limitation in immobilized enzyme particles may decrease the performance of kinetic resolution processes. In this paper a standard reaction plus diffusion model approach, based on homogeneous enzyme distribution, is used to verify experimentally the influence of the particle diameter on the observed enantioselectivity. This is done for a commercial preparation of immobilized Candida antarctica lipase B in the kinetic resolution of racemic 2-butanol by esterification with vinyl butyrate in heptane. For immobilized enzyme particles with particle diameters ranging from 355-710 μm the apparent enantiomeric ratio is constant at E^app = 2.5, while for ground particles with a particle diameter of 1 μm the intrinsic enantiomeric ratio is E = 4.4. This clear example of the influence of diffusion limitation on the observed enantioselectivity can not be described quantitatively in a straightforward way, because the enzyme seems to be present as a layer in the carrier particles.

Lipase-catalyzed direct amidation of free carboxylic acids is possible with ammonia in organic solvents. For butyric acid as a model compound the reaction proceeds well despite precipitation of ammonium butyrate, provided that the added molar amounts of butyric acid and ammonia are in the same range. The addition of ammonium salts is a convenient way to ensure suitable ammonia concentrations. Using Candida antarctica lipase B as the biocatalyst, the amidation proceeds well for various carboxylic acids and is very enantioselective in the amidation of 4-methyloctanoic acid.