Thermodynamic study on six tricyclic nitrogen heterocyclic compounds by thermal analysis and effusion techniques

Highlights: • Melting characteristics of tricyclic N-hetero tricyclic compounds were measured by DSC. • Vapor pressures of solid and liquid compounds were measured by effusion and iso-TG. • Thermochemical data from solid and liquid phases were compared with literature. • Good agreement between experimental and literature data with only few exceptions. - Abstract: The molar sublimation and vaporization enthalpies of acridine, phenanthridine, 1,7-phenanthroline, 1,10-phenanthroline, 4,7-phenanthroline and phenazine were determined at the averages of their respective experimental temperature ranges (Δ_cr^gH⁰_m () and Δ_l^gH⁰_m (), respectively) from the temperature dependencies of vapor pressure determined using Knudsen Effusion Mass Loss (KEML), Torsion Effusion (TE) and Isothermal Thermogravimetry (ITG) above their solid and liquid phases. The fusion characteristics (melting temperatures and the molar standard enthalpies of fusion at their melting temperatures) measured by Differential Scanning Calorimetry (DSC) were compared with the available literature values. Solid and liquid vapor pressure data determined by KEML, TE and ITG techniques as well as Δ_cr^gH⁰_m () and Δ_l^gH⁰_m () values, adjusted at 298.15 K by using the values of C_p(cr) and C_p(l) calculated by a well-known group additivity method, were found to be fairly correlated and are consistent with the available literature data. Final Δ_cr^gH⁰_m(298.15 K) values were also provided as weighted averages of all the available data.