PHASE-DIAGRAM OF (R)-4-HYDROXY-2-PYRROLIDONE 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-pyrrolidone presents a conglomerate in the racemic mixture. The enthalpy of melting extrapolated by the Schroder-van Laar-Le Chatelier equation [change in enthalpy (DELTAH) = 28410 J/mol; melting temperature (T(A)) = 429.9 K; solidus temperature (T(s)) = 395.4 K] and the value determined by differential scanning calorimetry (DELTAH = 28494 J/mol; T(A) = 429.6 K; T(s) = 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.