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The eutectic point in choline chloride and ethylene glycol mixtures.

ABSTRACT: The choline chloride (ChCl) and ethylene glycol (EG) mixture has become established as a paradigmatic deep eutectic solvent (DES). Here, we present measurements of the phase behaviour of this mixture over a wide composition range, and provide an extended phase diagram. The eutectic point was found to lie at -28 ± 1 °C and 0.01 < x_ChCl < 0.02, sharply contrasting with the previously expected eutectic composition. Our observations confirm that the eutectic temperature is not 'deep' compared to the ideal solution theory prediction. We also observe a cold-crystallisation at T = -65 °C which may have been formerly misinterpreted as the eutectic point.

SUBMITTER: Hayler HJ

PROVIDER: S-EPMC9665103 | biostudies-literature | 2022 Nov

REPOSITORIES: biostudies-literature

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The eutectic point in choline chloride and ethylene glycol mixtures.

Hayler Hannah J HJ Perkin Susan S

Chemical communications (Cambridge, England) 20221115 91

The choline chloride (ChCl) and ethylene glycol (EG) mixture has become established as a paradigmatic deep eutectic solvent (DES). Here, we present measurements of the phase behaviour of this mixture over a wide composition range, and provide an extended phase diagram. The eutectic point was found to lie at -28 ± 1 °C and 0.01 < <i>x</i><sub>ChCl</sub> < 0.02, sharply contrasting with the previously expected eutectic composition. Our observations confirm that the eutectic temperature is not 'dee ...[more]

PMID: 36314432

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Project description:The addition of molecular liquid cosolvents to choline chloride (ChCl)-based deep eutectic solvents (DESs) is increasingly investigated for reducing the inherently high bulk viscosities of the latter, which represent a major obstacle for potential industrial applications. The molar enthalpy of mixing, often referred to as excess molar enthalpy H E-a property reflecting changes in intermolecular interactions upon mixing-of the well-known ChCl/ethylene glycol (1:2 molar ratio) DES mixed with either water or methanol was recently found to be of opposite sign at 308.15 K: Mixing of the DES with water is strongly exothermic, while methanol mixtures are endothermic over the entire mixture composition range. Knowledge of molecular-level liquid structural changes in the DES following cosolvent addition is expected to be important when selecting such "pseudo-binary" mixtures for specific applications, e.g., solvents. With the aim of understanding the reason for the different behavior of selected DES/water or methanol mixtures, we performed classical MD computer simulations to study the changes in intermolecular interactions thought to be responsible for the observed H E sign difference. Excess molar enthalpies computed from our simulations reproduce, for the first time, the experimental sign difference and composition dependence of the property. We performed a structural analysis of simulation configurations, revealing an intriguing difference in the interaction modes of the two cosolvents with the DES chloride anion: water molecules insert between neighboring chloride anions, forming ionic hydrogen-bonded bridges that draw the anions closer, whereas dilution of the DES with methanol results in increased interionic separation. Moreover, the simulated DES/water mixtures were found to contain extended hydrogen-bonded structures containing water-bridged chloride pair arrangements, the presence of which may have important implications for solvent applications.

Dataset Information

The eutectic point in choline chloride and ethylene glycol mixtures.

Publications

The eutectic point in choline chloride and ethylene glycol mixtures.

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