Thermodynamics of mixtures with strong negative deviations from Raoult's law. XVIII: Excess molar enthalpies for the (1-alkanol + cyclohexylamine) systems at 298.15 K and modelling

Excess molar enthalpies, H-m(E), have been measured using a Tian-Calvet microcalorimeter for the systems CH3(CH2)(u-1)OH (u = 1,2,3,4,7,10) + cyclohexylamine at 298.15 K and 0.1 MPa. The H-m(E) values are large and negative, indicating the existence of strong interactions between unlike molecules, which is consistent with the also large and negative excess molar volumes, V-m(E) of these solutions, previously measured by us. The contribution from the equation of state term to H-m(E) has been evaluated for the 1-alkanol + cyclo hexylamine, or + 1-hexylamine, or + aniline mixtures, and the corresponding excess molar internal energies at constant volumes, U-m,V(E), determined. It is shown that such contribution is particularly important for the methanol + aniline system, in such way that the excess functions H-m(E) and U-m,V(E) have different sign at x(1) = 0.5. The DISQUAC and ERAS models have been applied to the cyclohexylamine systems, and the interaction parameters reported. DISQUAC improves ERAS results on H-m(E). The latter model describes correctly the V-m(E) curves. The variation of H-m(E) of CH3(CH2)(u-1)OH + cyclohexylamine, or + 1-hexylamine, or + aniline mixtures with u along a homologous series with a given amine, or with the amine in mixtures with a given 1-alkanol is discussed in terms of the different interactional contributions to H-m(E). (C) 2021 Elsevier Ltd.