Racemic compound formation–conglomerate formation. Part. 1. Structural and thermoanalytical study of hydrogen malonate, hydrogen phthalate and hydrogen succinate of α-phenylethylamine

Abstract

The crystal structure of (R,S)-α-phenylethylammonium hydrogen phthalate (RACPHP)[P2₁/a; a= 8.503(3), b= 16.748(5), c= 10.544(3)Å, β= 104.48(2)°; Z= 4; R= 0.058 based on 2412 observed reflections] and (R,S)-α-phenylethylammonium hydrogen malonate (RACPHM)[P; a= 8.768(1), b= 9.014(1), c= 7.485(1)Å, α= 104.31(1), β= 96.95(1), γ= 91.68(1)°; 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)-α-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.