Enthalpies of Vaporization and Vapor Pressures of Some Deuterated Hydrocarbons. Liquid−Vapor Pressure Isotope Effects

Abstract

Liquid−vapor pressures as a function of temperature and enthalpies of vaporization of a series of both liquid and solid hydrocarbons and their perdeuterated analogues have been determined by correlation−gas chromatography. The applicability of this technique is first demonstrated by reproducing the vapor pressure isotope effect of cyclohexane-d12 and benzene-d6. Other hydrocarbons studied include the perdeuterated forms of hexane, toluene, heptane, the p- and o-xylenes, naphthalene, biphenyl, acenaphthene, phenanthrene, anthracene, hexamethylbenzene, p-terphenyl, perylene, and chrysene. Vapor pressures and vaporization enthalpies of unlabeled hexamethylbenzene and perylene are also reported. Inverse vapor pressure isotope effects of the liquid phase are observed for all the substances examined. Vaporization enthalpy differences between unlabeled and labeled hydrocarbons are small and generally slightly positive. Vapor pressure−temperature relationships are reported in the form of a third-order polynomial that appears to reproduce experimental liquid−vapor pressures from T = 298.15 K to the boiling temperature.