RACEMIC COMPOUND FORMATION CONGLOMERATE FORMATION .1. STRUCTURAL AND THERMOANALYTICAL STUDY OF HYDROGEN MALONATE, HYDROGEN PHTHALATE AND HYDROGEN SUCCINATE OF ALPHA-PHENYLETHYLAMINE

The crystal structure of (R.S)-alpha-phenylethylammonium hydrogen phthalate (RACPHP) [P2(1)/a; a = 8.503(3), b = 16.748(5), c = 10.544(3) angstrom, beta = 104.48(2)-degrees; Z = 4; R = 0.058 based on 2412 observed reflections] and (R,S)-alpha-phenylethylammonium hydrogen malonate (RACPHM) [P1BAR; a = 8.768(l), b = 9.014(l), c = 7.485(l) angstrom, a = 104.31(l), beta = 96.95(l), gamma = 91.68(l)-degrees; Z = 2; R = 0.069 based on 2061 observed reflections] were determined and compared with each other and with the known crystal structure of the (R)-alpha-phenylethylammonium hydrogen succinate (KACBEV). The structural and thermoanalytical investigations of the salts proved that the hydrogen phthalate and hydrogen malonate anions form racemic compounds while the hydrogen succinate anion forms a conglomerate, the latter being the only one which could be resolved by preferential crystallization. The comparison of the structures revealed that the hydrogen bonding network of RACPHP [S(7)C22(9)R44(18)R88(30)C44(12)] and RACPHM [S(6)C22(8)R44(12)R44(16)] are very similar (represented by graph theory), while KACBEV [C11(7)C22(9)R33(8)R33(13)] is different. Intramolecular hydrogen bonds through acidic hydrogens are formed only between the carboxylic groups of the racemic compounds.