Phase Diagram of (R)- and (S)-4-Hydroxy-2-pyrrolidone Mixtures: A New Case of a Conglomerate-Forming System

The phase diagram of (R)- and (S)-4-hydroxy-2-pyrro(idone presents a conglomerate in the racemic mixture. The enthalpy of melting extrapolated by the Schröder-van Laar-Le Chatelier equation [change in enthalpy (ΔH) = 28410 J/mol; melting temperature (TA) = 429.9 K; solidus temperature (Ts) = 395.4 K] and the value determined by differential scanning calorimetry (ΔH = 28494 J/mol; TA = 429.6 K; Ts= 394.6 K) are in excellent agreement. The experimental entropy of the mixing of enantiomers is 5.69 J/mol ⋅ K. The conglomerate nature of the racemic mixture was confirmed by X-ray and IR spectroscopy. The presence of solvates was also observed.