Thermodynamic Properties of 1,4-Benzoquinones in Gaseous and Condensed Phases: Experimental and Theoretical Studies

A complete study of thermodynamic properties of 1,4-benzoquinones in the condensed and gaseous phases was carried out using experimental techniques and theoretical approaches. Enthalpies of combustion and formation of 2-methyl-1,4-benzoquinone were evaluated using combustion calorimetry. The transpiration method was utilized to determine the temperature dependence of the vapor pressures of 1,4-benzoquinone and 2-methyl-1,4-benzoquinone for the sublimation and vaporization enthalpies calculation. The group additivity scheme was used independently for verification of sublimation enthalpy of 2-methyl-1,4-benzoquinone. For this procedure the enthalpy of solution of 2-methyl-1,4-benzoquinone in benzene was measured at 298.15 K. The experimental values obtained were combined with published data and organized to obtain a reliable set of the experimental enthalpies of formation and enthalpies of phase transition of compounds. The methods of quantum chemistry and statistical physics based on the “rigid rotator–anharmonic oscillator” model were used to calculate thermodynamic functions of 1,4-benzoquinones in the ideal gas state in the temperature range 273.15–1500 K. The strain enthalpy and the enthalpy of π-conjugation were also estimated