An examination of the thermodynamics of fusion, vaporization, and sublimation of (R,S)- and (R)-flurbiprofen by correlation gas chromatography

The vaporization, fusion, and sublimation enthalpies of (R,S)- and (R)-flurbiprofen at T = 298.15 K are reported and compared with literature values when available. Correlation gas chromatography experiments were first performed to identify appropriate standards that could be used for materials containing a single fluorine substituent. Subsequent correlations resulted in a vaporization enthalpy for (R,S)-flurbiprofen and (R)-flurbiprofen, ?Hvap(298.15 K), of (127.5 +/- 5.5) and (127.4 +/- 4.7) kJ mol, respectively. Fusion enthalpies, ?Hfus(387 K), of (28.2 +/- and, ?Hfus(381 K), (22.8 +/- kJ mol-1 were also measured by differential scanning calorimetry for the racemic and chiral forms of flurbiprofen. Adjusted to T = 298.15 K and combined with the vaporization enthalpy resulted in sublimation enthalpies, ?Hsub(298.15 K), of (155.6 +/- 5.8) and (145.1 +/- 5.7) kJ mol-1 for (R,S)- and (R)-flurbiprofen, respectively. The fusion enthalpy measured for the racemic form was in excellent agreement with the literature value, while the sublimation enthalpy varies substantially from previous work. Two weak solidsolid phase transitions were also observed for (R)-flurbiprofen at T = 353.9 K (0.30 +/- 0.1) and 363.2 K (0.21 +/- 0.03) kJ center dot mol(-1). (C) 2012 Wiley Periodicals, Inc. and the American Pharmacists Association J Pharm Sci 101:20452054, 2012