Can cholinium chloride form eutectic solvents with organic chloride-based salts?

Abstract

The high melting point of a large number of organic salts with potential ionic liquid-like properties, hinders their applicability as solvents. Considering the success of cholinium chloride on lowering the melting temperature of several substances and its success on forming deep eutectic solvents, this work studies its mixing with organic chlorides to lower their melting points producing eutectic ionic liquids. The solid-liquid phase diagrams for binary mixtures composed of cholinium chloride and ten organic halides were experimentally measured. Surprisingly, cholinium chloride presented, for all these systems, significant positive deviations from ideal liquid behaviour that restricted its ability to lower the melting points of these mixtures. Only for mixtures with ammonium chloride, tetramethylammonium chloride, bis(2-hydroxyethyl)dimethylammonium chloride or cholinium bromide was cholinium chloride able to significantly lower the melting point of the mixture, but without reaching values close to room temperature (298 K). For a better understanding of the results obtained, the solid-liquid phase diagrams of four alkylammonium chloride-based mixtures were experimentally assessed and used to show that these compounds are better than cholinium chloride at inducing negative deviations from ideality, leading to greater melting point depressions.

The Role of Charge Transfer in the Formation of Type I Deep Eutectic Solvent-Analogous Ionic Liquid Mixtures

“…Figure 2 plots the melting curves and activity coefficients of [N 1,1,1,1 ]Cl in the chloride-based systems reported in Figure 1 and in the systems composed of [N 1,1,1,1 ]Cl and [N Bz,1,1,1 ]Cl, [NH 4 ]Cl, [N 2,2,2,2 ]Cl, or [N 3,3,3,3 ]Cl, which were previously published [21]. For visual simplicity, symmetric alkylammonium and benzyl alkylammonium systems are reported in separate diagrams.…”

“…Recently [21], whilst studying the capability of cholinium chloride to lower the melting point of organic chloride-based salts, we discovered that tetramethylammonium chloride presented severe deviations from thermodynamic ideality when mixed with tetraethylammonium chloride and tetrapropylammonium chloride. Based on the current prevailing understanding of dominating forces in eutectic solvents, such behaviour is unexpected, since these compounds are structurally very similar and are usually not regarded as strong hydrogen bond acceptors.…”

What a difference a methyl group makes – probing choline–urea molecular interactions through urea structure modification

“…A similar behaviour was observed by us in previous work, where cholinium chloride presented positive deviations from ideality when mixed with salts not able to act as hydrogen bond donors. 7 Raman spectroscopy provides further confirmation that the chloride anion prefers to interact with urea's N-H moieties and that the interaction becomes less favourable as the N-H are blocked by methylation. The strength of the N-HÁ Á Áchloride interactions can be inferred from the frequency of the NH stretching modes as depicted in Fig.…”

“…[1][2][3][4][5] They are usually defined as a mixture of a hydrogen bond acceptor (HBA) and a hydrogen bond donor (HBD) that form strong hydrogen bonds, 4 leading to melting temperatures substantially lower than those predicted by assuming an ideal liquid mixture 6 or those presented by the individual pure components. 5 Cholinium chloride (ChCl) is one of the most recurring substances used to prepare DES and a large set of experimental solid-liquid equilibrium data on mixtures containing ChCl is already available in the literature, [7][8][9][10][11] with most of the DES prepared presenting low toxicity and being readily biodegradable. 12,13 Even though the deep eutectic solvent composed of urea and cholinium chloride was identified as a green solvent in 2003, 14 its structure and molecular interactions, along with macroscopic phenomena such as solid-liquid equilibria (SLE), still hold some mysteries.…”

Using COSMO-RS to design choline chloride pharmaceutical eutectic solvents

“…Instead, only the data closer to the eutectic point were regressed. The systems choline chloride/octadecanoic acid [54] and choline chloride/ [N 2222 ]Cl [55]are displayed in Fig. 3 to exemplify both situations.…”