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The structures of the diastereomeric salts of (R)-(ϩ)-and (S)-(Ϫ)-3-(p-chlorophenyl)glutaramic acid with (S)-(Ϫ)-phenylethylamine have been determined by X-ray crystallography. Solubility and melting behaviours of the salts were analysed and correlated with their structural properties in the solid state. The (R)-(ϩ)-3-(p-chlorophenyl)glutaramic acid was converted to (R)-(Ϫ)-baclofen via a Hofmann degradation (57% yield, 99.8% ee, enantiomeric excess).

Co-crystal formation is of significant current interest, especially in the context of pharmaceutical development. 1 The reaction between the antibacterial sulfadimidine [4-amino-N-(4,6-dimethyl-2-pyrimidinyl)benzenesulfonamide] and a series of benzoic acid derivatives, both in the solid-state and in solution, yielded 1:1 co-crystals whose properties and solid-state reactions have recently been reviewed. 2 The title structure 1 (Fig. 1) is a representative member of this series, typified by the formation of the R(8) hydrogen bonded motif between the cocrystallizing partners. An earlier attempt to correlate the N-H·O and O-H·N distances comprising this specific R 2 2 (8) system with pKa differences between the co-crystal partners was partially successful, but was based on the X-ray structures of a series of analogs that contained only one co-crystal molecule in the asymmetric unit. 3 An examination of the title structure, however, with two molecules of the co-crystal in the asymmetric unit, allows possible effects of the crystal packing on the variability of the hydrogen bonded parameters to be distinguished.Colorless crystals of 1 were grown by the slow evaporation of an acetonitrile solution containing an equimolar mixture of sulfadimidine and p-chlorobenzoic acid. As proven by PXRD analysis, the identical phase could also be obtained by solidstate co-grinding of the components in a ball-mill for 10 min. Although sulfadimidine and p-chlorobenzoic acid yielded DSC fusion endotherms peaking at 197 and 243˚C, respectively, 1 melted at 207˚C. Co-crystal formation was also confirmed by shifts of the N-H infrared stretching bands of pure sulfadimidine (3436, 3337, 3236 cm -1 ) to significantly higher frequencies in the product (3469, 3376, 3256 cm -1 ). Intensity data were measured from a crystal of size 0.38 ¥ 0.38 ¥ 0.40 mm at room temperature (294 ± 2 K), and were corrected for Lp and absorption effects. With Z = 8, the space group P21/c requires the asymmetric unit to comprise two cocrystal units. The structure was solved by direct methods and refined by full-matrix least-squares on F 2 using SHELXL 97. All hydrogen atoms were located unequivocally in difference

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