Liquid-liquid equilibria for (2-hydroxy benzaldehyde + n-alkane) mixtures. Intermolecular and proximity effects in systems containing hydroxyl and aldehyde groups

TL;DR

This study investigates liquid-liquid equilibria and intermolecular interactions in mixtures of salicylaldehyde with alkanes and alcohols, revealing critical solution temperatures, interaction types, and thermodynamic behavior using experimental and modeling approaches.

Contribution

It provides new LLE data, analyzes intermolecular effects, and introduces a specific group in DISQUAC modeling for salicylaldehyde systems.

Findings

All systems exhibit an upper critical solution temperature increasing with alkane chain length.

Interactions in alcohol mixtures are mainly dipolar, with large positive excess enthalpies.

DISQUAC accurately models thermodynamic properties, incorporating a new group for salicylaldehyde.

Abstract

The liquid-liquid equilibrium (LLE) curves have been determined for the 2-hydroxyl-benzaldehyde (salicylaldehyde, SAC) + CH$_3$(CH$_2$)$_n$CH$_3$ mixtures ($n$ = 5,6,7,8,9). The equilibrium temperatures were determined observing, by means of a laser scattering technique, the turbidity produced on cooling when a second phase takes place. All the systems show an upper critical solution temperature, which linearly increases with $n$. Intermolecular effects have been investigated in alkanol + benzaldehyde systems using data from the literature. Interactions in 1-alkanol mixtures are mainly of dipolar type. The corresponding excess molar enthalpies, $H_{\text{m}}^{\text{E}}$, are large and positive, which reveals that interactions between like molecules are dominant. Interactions between unlike molecules are stronger for the methanol-containing system. For the other mixtures, the enthalpy of the (1-alkanol)-benzaldehyde interactions remains more or less constant. At 298.15 K and equimolar composition, the replacement of a linear polar solvent by the isomeric aromatic one leads to increased $H_{\text{m}}^{\text{E}}$ values in systems with a given 1-alkanol. The phenol + benzaldehyde system shows strongly negative deviations from the Raoult's law. Proximity effects have been examined in SAC + hydrocarbon mixtures. Alkane-containing systems are essentially characterized by dipolar interactions, while dispersive interactions are prevalent in the solution with benzene. All the mixtures have been treated in terms of DISQUAC. The interaction parameters for the OH/CHO contacts and for the SAC/aromatic and SAC/alkane contacts have been reported. DISQUAC provides a correct description of the thermodynamic properties considered. In the case of SAC systems, this is done by defining a new specific group HO-C-C-CHO for salicylaldehyde.