Vapour pressures and enthalpies of vaporization of a series of the alkylbiphenyls

Vapour pressure of 2-methyl-biphenyl, 3-methyl-biphenyl, 4,4′-di-methyl-biphenyl, 3-iso-propyl-biphenyl, 3-tert-butyl-biphenyl and 4,4′-di-tert-butyl-biphenyl were measured by the transpiration method. Vapour pressure of 3-iso-propyl-biphenyl, 3-tert-butyl-biphenyl and 4-tert-butyl-biphenyl measured by ebulliometry. Equations for temperature dependences of the saturated vapour pressures were derived. Molar standard enthalpies of vaporization at the reference temperature were calculated from temperature dependences of vapour pressures. Additionally, enthalpies of vaporization of 3-iso-propyl-biphenyl were directly measured in the temperature range from 323 to 373 K using an isothermal heat conducting Calvet microcalorimeter. The enthalpy of vaporization at the reference temperature 298 K of 3-iso-propyl-biphenyl was calculated from the experimental temperature dependence of vaporization enthalpy. The Ambrose–Walton equation was applied for correlation and prediction of vapour pressures and vaporization enthalpies of alkyl-substituted biphenyls.