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We investigated the enantiomeric enrichment of enantiomeric mixtures of alpha-phenylethylamine by achiral dicarboxylic acids. As achiral agents oxalic, malonic, fumaric, and phthalic acids were used. The results of the enantiomeric enrichment via partial salt formation followed by distillation were compared with enantiomer separation via crystallization of the neutral salt. Without the presence of a solid phase, enantiomeric separation is impossible. Our results show that the properties of the solid phase determine the separation. It is also confirmed by our observation that the eutectic points, which are observed on the 3-phase solubility diagrams of the solid neutral salts, can be found at the same initial enantiomeric composition as the point of intersection of distillate and residue of the distillation curves and the point of intersection of precipitated salt and mother liquor of the crystallization curves. Copyright 2000 Wiley-Liss, Inc.

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Acidic salts of eight achiral dicarboxylic acids with a-phenylethylamine are prepared and investigated by IR and density measurements, and X-ray crystallography to distinguish between racemic compound and conglomerate formation. It was found that conglomerate formation takes place when the protonated and deprotonated carboxylic groups form hydrogen bonded chains rather than forming cyclic intramolecular hydrogen bonds. Racemic compound formation, and indeed intramolecular H-bond formation, seems to be preferred when the two carboxylates are constrained in the same plane close to each other by a double bond, or they are ortho-substituents of a planar ring. The rules found for conglomerate formation of acidic salts of a-phenylethylamine are compared with Saigo's rules for conglomerate formation. The crystal structure of the conglomerate forming (R)-a-phenylethylammonium hydrogen itaconate is (OARPHI) also presented and the optical resolution by preferential crystallization is described. The hydrogen bonding network of OARPHI [ N l = C(7)C;(6), N, = R:(8)Rg(22)] is very similar to the hydrogen bonding network of the other conglomerate forming salt of this series: a-phenylethylammonium hydrogen succinate [ Nl = C(7) C;(9), N, = R:(8)R:( 13)].