Acetamidobenzoic acid isomers: Studying sublimation and fusion processes and their relation with crystal structures

• Thermodynamic characteristics of sublimation process were investigated for 2-, 3- and 4-acetamidobenzoic acids.
• Thermophysic parameters of melting processes were determined and enthalpies of vaporization were calculated for the isomers.
• Sublimation thermodynamic parameters were compared with crystal structures of the isomers.

Temperature dependencies of saturated vapor pressure for i-acetamidobenzoic acids (i = 2, 3 and 4) were obtained by flow inert gas-carrier transfer method. Thermodynamic parameters of sublimation were calculated for 2-acetamidobenzoic acid (2-AcAm-BA), 3-acetamidobenzoic acid (3-AcAm-BA) and 4-acetamidobenzoic acid (4-AcAm-BA) (2-AcAm-BA: ΔGsub298=54.4 kJ mol−1; ΔHsub298=116±1 kJ mol−1; ΔSsub298=205±4 J K−1 mol−1; 3-AcAm-BA: ΔGsub298=73.2 kJ mol−1; ΔHsub298=137±1 kJ mol−1; ΔSsub298=215±4 J K−1 mol−1; 4-AcAm-BA: ΔGsub298=72.3 kJ mol−1; ΔHsub298=138±1 kJ mol−1; ΔSsub298=221±8 J K−1 mol−1). Thermochemical parameters of fusion process for investigated substances were obtained, and vaporization enthalpies were estimated from fusion and sublimation enthalpies. The thermal data obtained in all experiments were used to find relationships between the thermal properties of these compounds and other benzoic acid derivatives and their structural properties. A correlation between enthalpy of sublimation and melting point was obtained. The influence of size and position of substituents on crystal lattice energy was discussed.

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