The thermodynamic stability of the three isomers of methoxybenzamide: An experimental and computational study

• Vapour pressures of the crystalline methoxybenzamides were measured.
• Enthalpies and entropies of sublimation and combustion were determined.
• Temperature and enthalpy of fusion were determined using DSC.
• Enthalpies and standard Gibbs free energies of formation and isomerization are presented.
• Gas-phase enthalpies of formation were estimated at the G3 and G4 levels.

Thermodynamic properties of ortho, meta and para methoxybenzamides were determined using the Knudsen effusion method and calorimetric experiments as well as computational approaches. The vapour pressure of the crystalline phase of the three isomers was measured and values of the standard (po = 0.1 MPa) molar enthalpy, Gibbs energy and entropy of sublimation, at T = 298.15 K, were derived. Static bomb combustion calorimetry was used to measure the standard molar enthalpies of combustion from which the standard molar enthalpies of formation in the crystalline state, at T = 298.15 K, were derived. Together with the standard molar enthalpies of sublimation, these results yielded the standard molar enthalpies of formation in gaseous phase of the three isomers. The standard Gibbs energies of formation in crystalline and gaseous phases were also derived and used to differentiate the thermodynamic stability of the three isomers. Moreover, differential scanning calorimetry analysis enabled determination of the temperature and molar enthalpies of fusion of the studied compounds. Gas-phase enthalpies of formation of the three compounds were estimated computationally at the G3 and G4 levels of theory and compared with the experimental results.