Racemic mixtures of chiral compounds that crystallize as conglomerate mixtures may be optically resolved using the technique of direct preferential crystallization. The method is based on the selective deposition of enantiomers from supersaturated solution onto optically pure seed crystals provided for this purpose. The technique has inherent advantages in its avoidance of the chiral auxiliaries and additional process chemistry that are characteristic of other methods for producing optically pure drugs. While preferential crystallization has been applied successfully to produce several important chiral compounds, it would undoubtedly be more widely used were it not for the fact that selective crystallization can be a difficult process to control on the large scale. It is proposed to examine the feasibility and potential benefits of membrane-stabilized preferential crystallization for stereoisomer separations. In the novel process, selective membranes are used to confine individual enantiomers and seed in such away as to enhance the stability of crystallization and thereby to improve process reliability and efficiency.
