L.L. Pashchenko

Thermodynamics of vaporization of some cyclic perfluorocarbons

The temperature dependence of the saturation vapor pressure of perfluoro-meta-dimethylcyclohexane, (CF3)2C6F10, has been determined by the ebulliometric method in the moderate pressure range from 8.4 to 101.6 kPa. Enthalpies of vaporization have been obtained calorimetrically for perfluorobicyclo(4,4,0)dec(1,6)ene, C10F16, and (CF3)2C6F10 at T = 298.15 K. Densities of C10F16 have been measured in the small temperature range from 293 to 338 K. Critical parameters have been estimated from vapor pressure data and densities for the substances under study and for some mono- and bicyclo-perfluorocarbons investigated earlier. A second-order group additivity method has been applied to predict the vaporization enthalpies of some cyclic perfluorocarbons.

The enthalpies of vaporization of some hydrocarbons with three-membered rings

The enthalpies of vaporization of four compounds with three-membered rings (bicyclopropyl, 1,2-bicyclopropylacetylene, 1-cyclopropylpentadiine-1,3, and 1,2,2-trimethylcyclopropene) were determined calorimetrically. The temperature dependence of saturated vapor pressure of 1,2,2-trimethylcyclopropene was studied by ebulliometry, and the results were approximated by the equation lnp = A + B/T. The enthalpy of vaporization, normal boiling temperature, critical parameter, and similarity criterion according to the law of corresponding states in the variant suggested by Filippov were calculated. The calculated corrections to the enthalpy of vaporization (kJ/mol) for the cyclopropene ring containing methyl substituents are discussed in comparison with the data on related compounds.

Standard enthalpies of formation of 4-methylbiphenyl and 4,4′-dimethylbiphenyl

The energies of combustion of 4-methylbiphenyl and 4,4′-dimethylbiphenyl in the crystal state were measured in a precision calorimeter equipped with a self-sealing bomb at 298.15 K. The enthalpies of vaporization of these substances were measured in an isothermal heat-conducting Calvet microcalorimeter. Standard enthalpies of formation were calculated for 4-methylbiphenyl and 4,4′-dimethylbiphenyl in the crystal, liquid, and gas states.