Thermodynamics Research Center / ThermoML | Journal of Chemical and Engineering Data

ABSTRACT

A newly developed static apparatus, capable of measuring the vapor pressure in the temperature range 273 368 K and in the pressure range 0.1 1333 Pa, is presented. The apparatus was calibrated by measuring the vapor pressure of recommended reference materials, naphthalene, n-decane, and ferrocene, and thoroughly tested. Subsequently, new vapor pressure data for benzophenone were measured in the temperature range 293 365 K with the aim to establish revised thermophysical data for this compound. Although benzophenone is another material recommended as the reference material for sublimation pressure and enthalpy measurements, the published sublimation thermodynamic data show a significant spread, and the recommendation was made with reservations which involved a reported metastable crystalline phase. We clarify this point based on reviewing the literature reporting the phase behavior and crystallographic studies and an extensive study on the polymorphic behavior of benzophenone performed in the present work. These findings are put in context with the studies reporting thermodynamic properties in which the authors were not aware of polymorphic behavior of benzophenone. The experimental data on vapor pressure for benzophenone were supplemented by ideal-gas heat capacities calculated by combining statistical thermodynamics and density functional theory (DFT) calculations. Calculated ideal-gas heat capacities and critically assessed experimental data on vapor pressure, condensed phase heat capacities, and sublimation enthalpies were subsequently treated simultaneously to obtain a consistent description of vaporization and sublimation thermodynamic properties of benzophenone.