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

Abstract

Excess molar enthalpies, HEm have been measured using a Tian-Calvet microcalorimeter for the systems CH 3 (CH 2 ) u -1 OH ( u =1,2,3,4,7,10) + cyclohexylamine at 298.15 K and 0.1 MPa. The HEm 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, VEm of these solutions, previously measured by us. The contribution from the equation of state term to HEm has been evaluated for the 1-alkanol + cyclohexylamine, or + 1-hexylamine, or + aniline mixtures, and the corresponding excess molar internal energies at constant volumes, UEmv, determined. It is shown that such contribution is particularly important for the methanol + aniline system, in such way that the excess functions HEm and UEmv 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 HEm. The latter model describes correctly the VEm curves. The variation of HEm of CH 3 (CH 2 ) 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 HEm.