The Role of Polyfunctionality in the Formation of [Ch]Cl-Carboxylic Acid-Based Deep Eutectic Solvents

Abstract

Aiming at providing an extensive characterization of the solid–liquid equilibria (SLE) of deep eutectic solvents (DESs), the phase diagrams of nine eutectic mixtures composed of choline chloride ([Ch]Cl) and (poly)carboxylic acids, commonly reported in the literature as DESs, were measured experimentally. Contrarily to the behavior reported for eutectic mixtures composed of [Ch]Cl (hydrogen-bond acceptor, HBA) and monofunctional hydrogen-bond donors (HBD) such as fatty acids and fatty alcohols, which have recently been shown to be almost ideal mixtures, a significant decrease of the melting temperature, at the eutectic point, was observed for most of the systems studied. This melting temperature depression was attributed to a pronounced nonideality of the liquid phase induced by the strong hydrogen-bond interactions between the two mixture components. Perturbed-chain statistical associating fluid theory (PC-SAFT) was used to describe these interactions physically. PC-SAFT allowed accurately modeling the e...