Impact of water on the melting temperature of urea + choline chloride deep eutectic solvent

Xiao, Meng; Ballerat‐Busserolles, Karine; Husson, Pascale; Andanson, Jean‐Michel

doi:10.1039/c5nj02677f

Cited by 156 publications

(143 citation statements)

References 20 publications

(39 reference statements)

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“…The presence of several exothermic transitions indicates the existence of different crystal structures at different temperatures [41]. So-called cold crystallization (when a low-temperature metastable state turns into a stable crystalline state, which only happens during heating) is highly dependent on the heating rate [41,42]. Such effects have also been described previously for pyrrolidinium [43], imidazolium [41], and pyridinium [13] ILs, and for binary IL mixtures [44].…”

Section: [Ch][lac]supporting

confidence: 59%

Influence of Carboxylate Anions on Phase Behavior of Choline Ionic Liquid Mixtures

et al. 2020

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Mixing ionic liquids is a suitable strategy to tailor properties, e.g., to reduce melting points. The present study aims to widen the application range of low-toxic choline-based ionic liquids by studying eight binary phase diagrams of six different choline carboxylates. Five of them show eutectic points with melting points dropping by 13 to 45 • C. The eutectic mixtures of choline acetate and choline 2-methylbutarate were found to melt at 45 • C, which represents a remarkable melting point depression compared to the pure compounds with melting points of 81 (choline acetate) and 90 • C (choline 2-methylbutarate), respectively. Besides melting points, the thermal stabilities of the choline salt mixtures were investigated to define the thermal operation range for potential practical applications of these mixtures. Typical decomposition temperatures were found between 165 and 207 • C, with choline lactate exhibiting the highest thermal stability.Advantages of DESs compared to pure ILs include easy preparation and therefore low production costs, increased biocompatibility in case of certain components, and bigger variety for customization concerning acidity, hydrophobicity, or polarity. DES systems have demonstrated their practical use in several applications, such as interfacial polymerizations [7], electrochemistry [8], and organic reactions [9].So far, the published research describing IL mixtures has mainly focused on imidazolium [10,11], pyrrolidinium [12], and pyridinium [13] ILs. In these works, significant melting point suppression effects were found for the respective eutectic mixtures. However, imidazolium, pyrrolidinium, and pyridinium ILs and their mixtures face some limitations when it comes to large-scale applications in contact with microorganisms or living matter [14]. Challenges include toxicity aspects and the cost for the organic cation synthesis. This is why a more detailed investigation of choline salts is highly interesting. Based on the available literature, choline salts are characterized by their low toxicity for different cell-lines [15,16], bacteria [17], and other organisms [18]. Moreover, choline salts are industrially available on a large scale.The most widely studied choline salt used in eutectic mixtures is choline chloride [19][20][21][22][23][24][25][26]. One of the first reported DESs was a mixture of choline chloride (liquefaction temperature 302 • C), and urea (melting point 134 • C) that resulted in a 2:1 molar mixture with a remarkable melting point suppression to 12 • C [4]. The typical strategy was to combine choline ILs with molecular compounds such as carboxylic acids, alcohols, and urea derivates [27], and such choline-based DESs have been used in various applications, e.g., as drug solubilization vehicles [28][29][30]. Note, however, that by mixing a choline IL with molecular substances, some of the very attractive IL properties, e.g., non-volatility, non-flammability, and high ionic conductivity can get lost to a large extent. This is why the mixing of two choline ILs is ...

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Section: [Ch][lac]supporting

confidence: 59%

Influence of Carboxylate Anions on Phase Behavior of Choline Ionic Liquid Mixtures

et al. 2020

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“…DESs are made of coordinating, hydrogen‐bonding ions and molecules, making them strongly water‐miscible and hygroscopic. Latent absorbed water is unavoidable, and impacts upon the physicochemical properties of DESs, such as the melting point, with inadequate characterization leading to poor reproducibility . A relatively new approach leverages the favorable physicochemical properties of DES/water mixtures, such as lowered viscosity .…”

Section: Figurementioning

confidence: 99%

“…High N coord values indicate important structural features in the disordered liquid. A discontinuity is observed at 1 w , a concentration chosen to reflect the latent absorbed water in DES . All DES interactions are weakened upon addition of 1 molar equivalent of water, except for the strengthened choline–urea hydrogen‐bonding interaction (OH⋅⋅⋅NH 2 ), which is reflected in the coordination numbers shown in the Supporting Information.…”

Section: Figurementioning

confidence: 99%

The Effect of Water upon Deep Eutectic Solvent Nanostructure: An Unusual Transition from Ionic Mixture to Aqueous Solution

2017

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The nanostructure of as eries of choline chloride/ urea/water deep eutectic solvent mixtures was characterized across aw ide hydration range by neutron total scattering and empirical potential structure refinement (EPSR). As the structure is significantly altered, even at lowh ydration levels, reporting the DES water content is important. However,t he DES nanostructure is retained to ar emarkably high level of water (ca. 42 wt %H 2 O) because of solvophobic sequestration of water into nanostructured domains around cholinium cations.A t5 1wt%/83 mol %H 2 O, this segregation becomes unfavorable,a nd the DES structure is disrupted;i nstead, water-water and DES-water interactions dominate.A ta nd abovet his hydration level, the DES-water mixture is best described as an aqueous solution of DES components.Deep eutectic solvents (DESs) are ac ompositionally diverse range (> 10 6 )oflow-transition-temperature mixtures, and represent as et of intrinsically "designer solvents", prepared by mixing hydrogen-bonding salts and neutral species in the eutectic molar ratio.[1] Thep hysicochemical properties of DESs are related to those of ionic liquids and their mixtures; [2] DESs are hybrid systems where molecular ionic clusters are found within ac omplex and disordered hydrogen-bonding network.[3] This nanostructure can be adjusted by selection of the mixing ratio and molecular chemical moieties, [4] and this additional degree of design freedom has aided the development of DESs as "greener" alternative media for organic and inorganic synthesis, [5] electrochemistry,s eparation, extraction, and biotransformations. [6] DESs are made of coordinating, hydrogen-bonding ions and molecules,m aking them strongly water-miscible and hygroscopic.L atent absorbed water is unavoidable,a nd impacts upon the physicochemical properties of DESs,s uch as the melting point, with inadequate characterization leading to poor reproducibility. [7] Arelatively new approach leverages the favorable physicochemical properties of DES/water mixtures,such as lowered viscosity.[8] Trends in these properties suggest that there is an upper limit to this hydration above which DESs are more like aqueous solutions.[9-11] However,it is not known how far such mixtures can be hydrated before they cease to be DESs on ananostructural level because only al imited compositional range has been probed experimentally in detail by NMR spectroscopy, [12] which has also been used extensively for ionic liquid (IL)/water mixtures. [13,14] The effect of water on DESs,a nd hence their classification, therefore remains one of the most significant unanswered questions in the field;dothey resemble ILs,ionic mixtures,or merely solutions of ions?H erein, we analyzed the nanostructure of the archetypal choline chloride/urea DES [15] across aw ide range of hydration. In doing so,w eh ave identified as tructure transition point from aD ES/water mixture to astate closer to an aqueous solution of individually solvated DES components.T his fundamental insight will aid the understa...

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“…24 We also observe significant urea−urea clustering, indicative of hydrogen-bonded regions of urea molecules akin to concentrated aqueous urea solutions, 31 and similar to the solvation structure of HBD molecules in ionic liquids. 32 Due to the H-bonded nature of DESs, most are watermiscible and hygroscopic, 33 and DES-aqueous mixtures (up to 50 wt% H 2 O) display modified physical properties, such as drastically reduced viscosity. 34−37 Despite the potential utility of these greener media in applications, such as separation, 38 the role of this additional water has received little attention, and it is not fully known whether water affects the DES structure negatively or constructively, or forms a biphasic system.…”

Section: ■ Introductionmentioning

confidence: 99%

Resilience of Malic Acid Natural Deep Eutectic Solvent Nanostructure to Solidification and Hydration

et al. 2017

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Little is presently known about the unique nanostructure of deep eutectic solvents (DES). The order of the liquid-solid phase transition is contended and whether DES-water mixtures are merely aqueous solutions, or have properties dominated by the eutectic pair, is unclear. Here, we unambiguously show the structure of choline chloride-malic acid (malicine) as a liquid, and also in solid and hydrated forms, using neutron total scattering on D/H isotope-substituted samples, and quasi-elastic neutron scattering (QENS). Data were refined using empirical potential structure refinement. We show evidence for a stoichiometric complex ion cluster in the disordered liquid, with strong choline-chloride bonding and a hydrogen bond donor (HBD) contribution. The 1:1 eutectic stoichiometry makes these ionic domains more well-defined, with less HBD clustering than seen previously for reline. There is minimal structural difference for the solidified material, demonstrating that this DES solidification is a glass transition rather than a first order phase change. QENS data support this by showing a gradual change in solvent dynamics rather than a step change. The DES structure is mostly retained upon hydration, with water acting both as a secondary smaller HBD at closer range to choline than malic acid, and forming transient wormlike aggregates. This new understanding of DES structure will aid understanding of the properties of these novel green solvents on the molecular length scale in chemical processes, as well as giving an insight into the apparent role of natural DESs in plant physiology.

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Impact of water on the melting temperature of urea + choline chloride deep eutectic solvent

Abstract: The melting temperature of reline decreases linearly with the addition of water.

Cited by 156 publications

References 20 publications

Influence of Carboxylate Anions on Phase Behavior of Choline Ionic Liquid Mixtures

Influence of Carboxylate Anions on Phase Behavior of Choline Ionic Liquid Mixtures

The Effect of Water upon Deep Eutectic Solvent Nanostructure: An Unusual Transition from Ionic Mixture to Aqueous Solution

Resilience of Malic Acid Natural Deep Eutectic Solvent Nanostructure to Solidification and Hydration

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