Enthalpy of sublimation/vaporization of trans-cyclohexyl-1,4-diamine and cis-cyclohexyl-1,2-diamine

Abstract

The molar enthalpy of sublimation, Δ cr g H m ∘ , of trans-cyclohexyl-1,4-diamine and the molar enthalpy of vaporization, Δ l g H m ∘ , of cis-cyclohexyl-1,2-diamine, at the temperature 298.15 K, were determined by calorimetry. Δ cr g H m ∘ ( T = 298.15 K ) = ( 105.0 ± 0.8 ) kJ · mol - 1 was obtained for the trans-isomer and Δ l g H m ∘ ( T = 298.15 K ) = ( 62.2 ± 1.0 ) kJ · mol - 1 for the cis form. The molar enthalpy of fusion of the first compound, at T = 342.1 K, was determined by differential scanning calorimetry. The molar enthalpy of vaporization of the 1,4-isomer was estimated by combining the value of the enthalpy of sublimation with that of the enthalpy of fusion. The values obtained for molar standard enthalpy of vaporization and those available for the enthalpy of the diamines in the gas state were used to calculate the difference between the enthalpies of both compounds in the liquid state.