A combined experimental and computational thermodynamic study of fluorene-9-methanol and fluorene-9-carboxylic acid

Abstract

This work reports an experimental and computational thermodynamic study performed on two 9-fluorene derivatives: fluorene-9-methanol and fluorene-9-carboxylic acid. The standard (po=0.1MPa) molar enthalpies of formation in the crystalline phase of these compounds were derived from the standard molar energies of combustion, in oxygen, at T=298.15K, measured by static bomb combustion calorimetry. A static method, based on a capacitance diaphragm gauge, and a Knudsen effusion method were used to perform the vapour pressure study of the referred compounds, yielding accurate determination of the standard molar enthalpies and entropies of sublimation and vaporisation. For fluorene-9-carboxylic acid, the enthalpy of sublimation was also determined using Calvet microcalorimetry. The enthalpy of fusion of both compounds was derived indirectly from vapour pressure results and directly from DSC experiments. Combining the thermodynamic parameters of the compounds studied, the standard Gibbs energy of formation in crystalline and gaseous phases were derived as well as the standard molar enthalpy of formation in the gaseous phase. A theoretical study at the G3 and G4 levels has been carried out, and the calculated enthalpies of formation have been compared with the experimental values.