Molecular Recognition in the Formation of Conglomerate Crystal. 2. The Role of Arenesulfonic Acid in the Conglomerate Crystals of Amino Acid Salts

The structures of conglomerate crystals, p-chlorobenzenesulfonic acid salt of L-alanine, p-toluenesulfonic acid salt of L-serine, and benzenesulfonic acid salt of L-leucine, were determined by X-ray analysis. The crystals are built up of repeating units consisting of two amine components and two acid components to form a helical column by hydrogen bonds. The arrangements of the arenesulfonic acids are found to be similar to each other in these systems. Moreover, the arrangements have similarity to those of cinnamic acid in the crystals of cinnamic acid salts of (R)-1-phenylethylamine and of (R)-1-(4-isopropylphenyl)ethylamine, which are also conglomerates. These results suggest that our proposed criteria for the choice of an achiral derivatizing agent in the transformation of a racemic compound into a conglomerate crystal is appropriate.