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

TL;DR

This study measures excess molar enthalpies of specific alcohol-amine mixtures at 298.15 K, analyzes their strong negative deviations from ideality, and applies models to better understand molecular interactions and thermodynamic behavior.

Contribution

It provides new experimental data on excess molar enthalpies for 1-alkanol + cyclohexylamine systems and evaluates the effectiveness of DISQUAC and ERAS models in describing these mixtures.

Findings

Excess molar enthalpies are large and negative, indicating strong interactions.

The contribution from the equation of state is significant, especially for methanol + aniline.

DISQUAC model improves upon ERAS in predicting enthalpy, while ERAS accurately describes volume deviations.

Abstract

Excess molar enthalpies, $H_{\text{m}}^{\text{E}}$, 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 $H_{\text{m}}^{\text{E}}$ 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, $V_{\text{m}}^{\text{E}}$, of these solutions, previously measured by us. The contribution from the equation of state term to $H_{\text{m}}^{\text{E}}$ has been evaluated for the 1-alkanol + cyclohexylamine, or + 1-hexylamine, or + aniline mixtures, and the corresponding excess molar internal energies at constant volume, $U_{\text{m,}V}^{\text{E}}$, have been determined. It is shown that such contribution is particularly important for the methanol + aniline system, in such a way that the excess functions $H_{\text{m}}^{\text{E}}$ and $U_{\text{m,}V}^{\text{E}}$ have different sign at $x_1$ = 0.5. The DISQUAC and ERAS models have been applied to the cyclohexylamine systems, and the interaction parameters have been reported. DISQUAC improves ERAS results on $H_{\text{m}}^{\text{E}}$. The latter model describes correctly the $V_{\text{m}}^{\text{E}}$ curves. The variation of 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 $H_{\text{m}}^{\text{E}}$.