THE THERMODYNAMIC PROPERTIES TO THE TEMPERATURE 700 K OF NAPHTHALENE AND OF 2,7-DIMETHYLNAPHTHALENE

Measurements leading to the calculation of the standard thermodynamic properties of the gases are reported for naphthalene (Chemical Abstracts registry number [91-20-3]) and 2,7-dimethylnaphthalene (registry number [582-16-1]). Experimental methods included adiabatic heat-capacity calorimetry, comparative ebulliometry, and differential-scanning calorimetry (d.s.c.). The critical temperature was determined experimentally for each compound, and the critical pressure and critical density were derived from fitting procedures. Vapor-pressure measurements reported in the literature were compared with the results obtained in this research. Enthalpies of vaporization and sublimation were derived from the experimental measurements and compared with literature results. New self-consistent equations for the variation of sublimation pressure with temperature for naphthalene and 2,7-dimethyl-naphthalene were derived. For each compound, literature values for entropies and enthalpies of the liquid phase and the energy of combustion were combined with the present results to derive standard entropies, enthalpies, and Gibbs free energies of formation for the gaseous phase for temperatures between 298.15 K and 700 K. The standard properties for naphthalene(g) were compared with values obtained using statistical mechanics with various fundamental vibrational-frequency assignments available in the literature. A scheme to estimate the standard thermodynamic functions for gaseous alkylnaphthalenes was updated. the size of the barrier to methyl-group rotation in 2,7-dimethylnaphthalene was shown to be of about the same size as that for toluene. Values for standard entropies for 2-methylnaphthalene(g) in the temperature range 300 K to 700 K were estimated. © 1993 Academic Press Ltd.