Abstract
We review two methods of optical resolution using the crystal size difference between D- and L-crystals. As a first optical resolution technique, seeded cooling crystallization was performed with the L-Asn seeds of large size and the D-Asn seeds of small size. This method was experimentally proved as a useful method. The product crystals had a bi-modal distribution. The large crystals were L-Asn of 100 % purity and the small crystals were D-Asn of 100 % purity. As a second optical resolution technique, a "tailor-made" additive was used as a separation agent. As a model chiral compound, the conglomerate of asparagine was examined. By a batch cooling operation, the primary nucleation of L-Asn was delayed significantly by adding L-Cysteine at 5 mol %, while that of the other enantiomer, D-Asn, remained almost unchanged. The distribution of the product crystals was found to be bi-modal. The large crystals were D-Asn with 100 % optical purity.
