Insights into the Nature of Eutectic and Deep Eutectic Mixtures

Abstract

A stricter definition of a deep eutectic solvent (DES) is urgent, so that it may become a sound basis for further developments in this field. This communication aims at contributing to deepening the understanding of eutectic and deep eutectic mixtures concerning their definition, thermodynamic nature and modelling. The glut of literature on DES applications should be followed by a similar effort to address the fundamental questions on their nature. This hopefully would contribute to correct some widespread misconceptions, and help to establish a stringent definition of what a DES is. DES are eutectic mixtures for which the eutectic point temperature should be lower to that of an ideal liquid mixture. To identify and characterize them, their phase diagrams should be known, in order to compare the real temperature depression to that predicted if ideality is assumed, and to define composition ranges for which they are in the liquid state at operating temperatures. It is also shown that hydrogen bonding between the DES components should not be used to define or characterize a DES, since this would describe many ideal mixtures. The future of deep eutectic solvents is quite promising, and we expect that this work will contribute to the efficient design and selection of the best DES for a given application, and to model properties and phase equilibria without which the process design is impractical.

Using COSMO-RS to design choline chloride pharmaceutical eutectic solvents

“…5 illustrates these results. Although these results, in terms of absolute average deviations, do not seem to be much better than those obtained considering an ideal liquid mixture, even since as shown by us [2] many of these systems do not show a significant deviation to ideal behaviour, a simular representation presented in Fig. S4 shows that as the non ideality increases COSMO-RS is able to capture this for most systems with success.…”

“…Their liquid state at operation temperature arises from the mixing of two or more solid components (typically hydrogen bond acceptors and donors) presenting a eutectic temperature at or below the operation temperature. In this way, what is commonly named deep eutectic solvents are eutectic mixtures that are liquid at the operation temperature, where the prefix deep, although disputable [2], can be understood in two ways: to highlight the fact that these are eutectic mixtures that have large negative deviations from ideality, or to emphasize that the eutectic melting temperature is significantly lower than that of the original components [3].…”

“…Recently, however, Fernandez et al [17] were able to indirectly assess the melting temperature and enthalpy of choline chloride from solid-liquid equilibrium (SLE) data of a large number of systems. These properties were further appraised by Martins et al [2] Concerning the activity coefficients, the predictive model COSMO-RS, based on quantum chemistry, has been extensively used in the study of DES [18e29], but generally focusing in applications and/or specific systems and not in the analysis of phase diagrams, or in the prediction of eutectic points, as will be here explored.…”

High‐Molecular‐Weight Polyampholytes Synthesized via Daylight‐Induced, Initiator‐Free Radical Polymerization of Renewable Itaconic Acid

“…DOI: 10.1002/marc.201900611 mixtures [9] (LTTMs). Although they can contain relatively simple compounds such as choline chloride (CC), amides, carboxylic acids, sugars, and even water, their thermodynamic properties and molecular structure are subjects for intense debate [4] and investigations. [10,11] In every case, the importance of the mixtures for many fields of chemistry, including poly mers chemistry is indisputable.…”

“…Low-melting point binary or ternary mixtures based on small organic compounds or inorganic salts have attracted broad attention due to their possible use as a novel alternative to ionic liquids to be used use as media for chemical processes. [1][2][3][4][5][6] Due to the lack of strict definition, [4] the mixtures are commonly called deep eutectic solvents [1,7] (DESs), hydrophobic eutectic solvents, [6] natural deep eutectic solvents [3,8] (NADESs) or low-transition temperature viscous liquid is formed. The mixture shows no tendency to crystalize, presumably due to its high viscosity (13 000 mPa s at 21 °C, Table S1, Supporting Information).…”