The development of a phasic system for the enzymic resoln. of racemic phenylalanine (I) up to benchtop pilot plant scale is described. The principle is based upon the hydrolysis of racemic Pr ester of I with immobilized a-chymotrypsin (II) in which only the L-isomer reacts to give enantiomerically pure L-I. By employing Me2CHCH2COMe and H2O as solvents, several problems inherent to the monophasic system (such as substrate autohydrolysis, dimerization, or pptn. at high pH or severe pH decreases at the activity optimum of the enzyme (5.5-6.5) due to low buffer capacity) are overcome, since the immiscible org. phase partially exts. the neutral form of the ester, thus shifting the buffer capacity to optimal reaction values. 100% Conversions are thereby obtained without the necessity of external pH control. Various data are presented for monophasic, biphasic, and triphasic (ie. with immobilized II) systems, including conversions, substrate partitions between the 2 solvents, and reaction kinetics. Although batch expts. with the 3-phase system were successful in a continuously stirred tank reactor, in continuous operation in a plug flow reactor conversion did not exceed 80%, probably a result of mass transfer limitation between both liq. phases. [on SciFinder (R)]