Racemic Structure of DL-α-Phenylglycine Sulfate

Abstract

The racemic structure of DL-a-phenylglycine (DL-Phg) sulfate has been studied. DL-Phg sulfate forms a racemic compound at temperatures in the vicinity of the melting point, and the value of free energy of formation of the racemic compound is negative. However, it is suggested that the racemic compound becomes unstable with a decrease in temperature, since the enthalpy is positive. In the solubility ternary phase diagrams in 30 wt% H₂SO₄, the solubility curves at 10 and 20°C showed characteristic patterns of racemic compounds, while those at 0 and 5°C patterns of conglomerates. DL-Phg sulfate crystallized from a 30 wt%H₂SO₄the solution at 0°C showed an infrared spectrum identical to that of D-Phg sulfate, but the spectrum was different from that of DL-Phg sulfate crystallized at 20°C. It was possible to resolve DL-Phg sulfate by preferential crystallization procedure in 30 wt% H₂SO₄ at 15°C. These results indicate that DL-Phg sulfate forms the racemic compound at temperatures higher than 10°C and is conglomerate at temperatures lower than 5°C.