Racemic Structure and Optical Resolution by Preferential Crystallization of DL-Cysteine Salts of Substituted Benzenesulfonic Acids

Article abstract of DOI:10.1246/bcsj.60.3985

Infrared absorption spectrum, solubility, and thermodynamic analysis indicated that DL-cysteine salts of benzenesulfonic acid (DL-BA salt) and 4-ethylbenzenesulfonic acid (DL-4-EB salt) are conglomerates at room temperature, but DL-BA salt forms a racemic compound at the melting point.These DL-salts were optically resolved by the preferential crystallization.As for DL-4-EB salt, suitable conditions were estimated by the free energy of critical nucleation in supersaturated solutions.The successive preferential crystallization in ethanol at 20 deg C was found to give D- and L-4-EB salts with optical purity of 97-100percent in the resolution yield of 83-90percent.Purification and following treatment with triethylamine gave optically pure D- and L-Cys's.