(R)-Phenyl-ethyl-ammonium (R)-4-chloro-mandelate

Optical resolution of a racemic mixture of ()-4-chloro-mandelic acid (4-ClMA) was obtained using (R)-phenyl-ethyl-amine (R-PEA) as a resolving agent. A pair of diastereomeric salts (R-4-ClMA·R-PEA and S-4-ClMA·R- PEA) had significantly different solubilities and allowed optically pure crystals of the title complex, (R)-phenyl-ethyl-ammonium (R)-2-(4-chloro-phen- yl)-2-hydroxy-acetate, C8H12N⁺·C8H6ClO3 ^- or [(R)-C6H5C(H)CH3NH3][(R)-4-ClC6H4C(H)(OH)CO2], to be isolated. The crystal structure of the enanti-omeric S,S analogue has been published previously [Kinbara, Tagawa & Saigo (2001). Tetra-hedron Asymmetry, 12, 2927-2930]. In the title crystal structure, a two-dimensional network, perpendicular to the c axis, is formed via inter-molecular hydrogen bonds.