Choline-based Deep Eutectic Solvents Research Articles

Theoretical investigation on the structure and physicochemical properties of choline chloride-based deep eutectic solvents

Deep eutectic solvents (DESs) are analogous to ionic liquids that have been widely employed in scientific research and engineering applications. The physicochemical properties of DESs, including the density, viscosity, and nanostructure, serve as the foundation for green solvent development. In the present work, the density and viscosity of choline-based DESs at 293.15–353.15 K were simulated using molecular dynamics (MD) simulation under the Generation Amber Force Field. The radial distribution function (RDF) and number of hydrogen bonds of the selected systems were analysed. It was found that a large amount of the hydrogen bonding network was formulated between chlorine and hydrogen atoms in hydroxyl groups, which greatly decreased the melting temperature of the solvent in comparison with the pure components. The intermolecular interaction decreased with increasing temperature as well as the length of the alkyl chain on the hydrogen bond donor (HBD). Furthermore, an increase in the number of hydroxyl groups in HBD molecules leads to the formation of a more complex and extensive hydrogen bond network, which results in a higher viscosity of the DES.

Hydrogen bonds in aqueous choline chloride solutions by DFT calculations and X-ray scattering

Choline chloride (ChCl) is a common hydrogen bond acceptor (HBA) for deep eutectic solvents (DESs), and the hydrogen bonds between ChCl and H2O impact the physicochemical properties of DES-water mixtures. In the present work, the hydrogen bonds in aqueous ChCl solutions were investigated combining with Raman spectroscopy, density functional theory (DFT) calculations, X-ray scattering and empirical potential structure refinement (EPSR). The Ch+ in aqueous ChCl solutions mainly exists as the gauche conformation. The aqueous ChCl solutions were found to be stabilized by both classical hydrogen bonds (O-H⋯Y, Y = Cl, OW) and carbon-hydrogen bonds (C-H⋯Y, Y = OW) between the components. The orientation of the hydrogen bonds is close to linear (∼180°), while the orientation of the carbon-hydrogen bonds is relatively weak (150°∼176°). The existence of carbon-hydrogen bonds elucidates the high coordination of quaternary ammonium group with H2O. Carbon-hydrogen bonds are found in the partial radial distribution functions, the angle distribution functions and the atoms in molecules analysis. Hydrogen bonds and carbon-hydrogen bonds can affect the physicochemical properties of aqueous ChCl solutions and DES-H2O mixtures. This fundamental understanding of the aqueous ChCl solutions will enable future developments in functional design and application of choline-based DESs.

Liquid-liquid extraction and mechanism analysis of extracting fuel additive isopropanol from mixture with choline-based deep eutectic solvents as efficient extractants

Deep eutectic solvents (DESs) have wide application prospects in azeotropic separation since of their advantages of good thermal stability, non harmfulness and low raw material price. As a green solvent, DESs has attracted more and more attention in recent years. As a high-quality fuel additive, isopropanol (IPA) has high chemical added value because of its high energy density, low volatile and small corrosive. Therefore, extracting high alcohols such as IPA from azeotropes can effectively improve the combustion efficiency of fossil fuels and reduce tail gas emissions. In this work, ethylene glycol and other hydrogen bond receptors were selected to synthesize three choline-based DESs to extract IPA from n-heptane. The selectivity of DESs to IPA was obtained by liquid–liquid equilibrium (LLE) experiment and the separate efficiency of diverse DESs was compared. To profoundly investigate the intrinsic principle of extracting IPA from DESs, molecular dynamics (MD) simulation method was utilized to acquire the interaction energy between DESs and IPA/n-heptane, as well as the radial distribution function between DESs and IPA and other kinetic analysis data. The data showed that the experiment is in great assertion with the simulation, DESs synthesized from choline chloride and ethylene glycol has the leading extraction impact of IPA among three kinds of DESs, and Cl- played an imperative part in LLE. In addition, the effect of azeotrope ratio on separation efficiency was explored by simulating LLE with different azeotrope composition.

Choline based deep eutectic solvent mediated Friedlander annulation: A sustainable and regiospecific approach to polysubstituted quinoline

Polysubstituted quinolines have been synthesized by Friedlander annulation reaction of 2-aminobenzophenone with ketones mediated by choline-based deep eutectic solvents (DESs). We have investigated the condensation reaction in different choline-based DES and found choline chloride-zinc chloride DES to be the best catalyst with excellent yield of products. Moreover, regiospecificity was observed only under basic choline hydroxide medium in moderate yield. The deep eutectic solvent acts as dual role of solvent as well as catalyst and can be recycled. Mild reaction conditions, simple work-up procedure, excellent product yield, and use of recyclable catalyst are special features of this methodology, which makes the protocol a sustainable alternative to earlier reported methods of quinoline synthesis.

Phase behavior and extraction mechanism of methanol-n-hexane separation using choline-based deep eutectic solvent

Deep eutectic solvents (DESs) have attracted increasing attention as green solvents in recent years owing to their potential for use in azeotropic separation and their advantages, such as low vapor pressure, non-toxicity, and low cost. To separate methanol (MeOH)-n-hexane (NHA) azeotrope, three choline-based DESs were prepared using glycerol, ethylene glycol (EG), and urea as the hydrogen bond receptors. The liquid–liquid equilibrium (LLE) data of DES-MeOH-NHA were measured at 298.15 K and 1 atm. The distribution coefficient and selectivity were obtained to compare the extraction efficiencies of different DESs. To further explore the extraction mechanism of LLE, the molecular dynamics (MD) method was used to study the internal mechanism of MeOH extraction by DESs. In addition, the experimental and MD simulation data were compared. Based on the MD simulation, the interaction energies between DES and MeOH/NHA, radial distribution function, and spatial distribution function between DES and MeOH were obtained. In addition, the experimental results were in good agreement with the simulation results, and both the results established that choline chloride (ChCl)/EG(1:2) had the highest extraction efficiency for methanol among the three DESs. Additionally, MD simulation results showed that Cl- plays a vital role in the LLE, and the interaction force between Cl- and MeOH was primarily provided by the electrostatic force.

A Combined Deep Eutectic Solvent-Ionic Liquid Process for the Extraction and Separation of Platinum Group Metals (Pt, Pd, Rh).

Recovery of platinum group metals from spent materials is becoming increasingly relevant due to the high value of these metals and their progressive depletion. In recent years, there is an increased interest in developing alternative and more environmentally benign processes for the recovery of platinum group metals, in line with the increased focus on a sustainable future. To this end, ionic liquids are increasingly investigated as promising candidates that can replace state-of-the-art approaches. Specifically, phosphonium-based ionic liquids have been extensively investigated for the extraction and separation of platinum group metals. In this paper, we present the extraction capacity of several phosphonium-based ionic liquids for platinum group metals from model deep eutectic solvent-based acidic solutions. The most promising candidates, P66614Cl and P66614B2EHP, which exhibited the ability to extract Pt, Pd, and Rh quantitively from a mixed model solution, were additionally evaluated for their capacity to recover these metals from a spent car catalyst previously leached into a choline-based deep eutectic solvent. Specifically, P66614Cl afforded extraction of the three target precious metals from the leachate, while their partial separation from the interfering Al was also achieved since a significant amount (approx. 80%) remained in the leachate.

Molecular insight into the structure and dynamics of LiTf2N/deep eutectic solvent: an electrolyte for Li-ion batteries

ABSTRACT Two choline-based deep eutectic solvent namely ethaline and glyceline have been used in different applications such as metal extraction, solubility and in electrochemistry because of its easy availability, inexpensive and non-toxic nature. In this work, molecular dynamics simulation was employed to study the structural and transport properties of ethaline and glyceline when blended with Li+ based salt (lithium bis (trifluoromethane sulphonyl) imide (LiTf2N)) in varying concentrations for the application as electrolytes in lithium-ion batteries. The effect of temperature and concentration on the structural and transport properties was explored to understand the diffusion of Li+ at the atomic level. For both the deep eutectic solvents (DESs), all the H-bond between Cl − ion and hydrogen bond acceptor i.e. ethylene glycol/glycerol decreases due to the formation of a network between Li+ and Cl − upon increasing salt concentration. Li+ ions was found to be in the diffusive regime at a very high temperature ( > 400 K) and low molar concentration (< 0.2). It is interesting to note that, for the same salt concentration, self-diffusion coefficient of Li+ ion in ethaline was observed to be tenfold higher than in the glyceline. Therefore, this study provides a microscopic understanding to synthesise a choline-based electrolyte by addition of Li-salt.

Cytotoxicity of some choline-based deep eutectic solvents and their effect on solubility of coumarin drug

The effect of some deep eutectic solvents (DESs) on the coumarin solubility has been investigated using Hansen solubility parameters (HSP). The solubility of coumarin was measured in aqueous systems containing some DESs based on choline chloride (ChCl) as hydrogen bond acceptor (HBA) with urea (U), ethylene glycol (EG), and glycerol (GLY) as hydrogen bond donors (HBD) by widely applied shake-flask method at T = (298.15 to 313.15) K. The results indicate that coumarin solubility enhances with the concentration of DESs and temperature. Also, coumarin was dissolved more than 80 times compared with pure water in the presence of ChCl/EG. Then experimental data were fitted to Wilson, electrolyte Non-Random Tow-Liquid (e-NRTL), and UNIQUAC activity coefficient models. Furthermore, the dissolution thermodynamic properties including enthalpy, Gibbs free energy, and entropy have been calculated based on Gibbs and van't Hoff equations. Due to these results, it is indicated that coumarin dissolution in the studied systems is an endothermic process. Moreover, to investigate the biological properties of DESs, MTT assay have been applied to determinate cytotoxicity of the DESs. In the melanoma skin cell line, cell culture tests revealed that these solvents had very low toxicity and high biocompatibility.

Study of naproxen dissolution in the mixtures of a choline-based deep eutectic solvent + water at different temperatures

To improve the solubility of a weakly water-soluble drug of naproxen, a deep eutectic solvent (DES) based on choline chloride with propylene glycol as a green solvent is applied from 0.0 up to 1.0 mass fractions of DES at T = (293.2 to 313.2) K. Five cosolvency models including Jouyban-Acree, Jouyban-Acree-van't Hoff, van't Hoff, the mixture response surface and the Buchowski–Ksiazczak models were used to correlate the generated solubility data. The mean relative deviations (MRD %) is applied for the accuracy investigation of the models. Moreover, the respective apparent thermodynamic quantities of the dissolution and solvation processes, namely Gibbs energy, enthalpy, and entropy, are also calculated based on the van’t Hoff and Gibbs equations.

Insights into the orientation and hydrogen bond influence on thermophysical and transport properties in choline-based deep eutectic solvents and methanol

The search for new solvents which fulfil the needs of modern times has put the Deep eutectic solvents (DESs) in a leading role given their wide range of applications, versatility, low cost, and minimal environmental impact. For the above reason, it is critical to achieving predictive capabilities and the accurate description of their properties, both macroscopic and microscopic. In this work, DESs based on choline chloride as the hydrogen bond acceptor plus ethylene glycol and glycerol as hydrogen bond donors have been analysed in a mixture with methanol. Densities, excess volume and viscosity were determined by molecular dynamics and predicted by the perturbed-chain statistical associating fluid theory equation of state (PC-SAFT EOS). Radial distribution functions and the number of hydrogen bonds derived from molecular simulations confirmed an anticipated bonding network within the liquid, with significant ordering interactions. When methanol is added to the eutectic solvent become incorporated into this structure as a second hydrogen bond donor. Methanol reduces the viscosity, but the eutectic solvents retain their characteristics. The analysis performed in this work could be a valuable feature of the new theory in developing more realistic models of the hydrogen-bonding interaction in deep eutectic solvents.

Choline-based deep eutectic solvent combined with EDTA-2Na as novel soil washing agent for lead removal in contaminated soil

Lead-contaminated soil was cleaned through ethylene-diamine-teraacetic acid disodium salt (EDTA-2Na) combined with diluted deep eutectic solvent (DES) which was prepared by mixing choline chloride with ethylene glycol. The influences of leaching temperature, leaching time, liquid-solid (L/S) ratio, concentration of EDTA-2Na, water-DES ratio, and the molar ratio of choline chloride-ethylene glycol (Ch-E) on the leaching rate of lead were investigated. The mineral phases of the soil and DES before and after washing were analyzed using scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FT-IR). The changes to the DESs before and after dissolving lead nitrate (Pb(NO3)2) were analyzed by high resolution mass spectrometry (HRMS) and nuclear magnetic resonance (NMR). Hydrogen bonds and EDTA-2Na in the Ch-M system resulted in the conversion of Pb(NO3)2 to other complex ions such as [Pb·Ch-E]− and [Pb·EDTA-2Na]− and other complex ions due to the dissolution of the washing agent. The results showed that the soil mineral phase did not change significantly and up to 95.79% of Pb could be washed under temperature, time, L/S ratio, EDTA-2Na concentration, DES/water ratio, Ch-E molar ratio, and stirring speed conditions of 40 °C, 2 h, 6, 0.02 M, 2, 0.75 and 300 rpm, respectively. The hydrogen bonds and EDTA-2Na may play a key role in the remediation of lead-contaminated soil by a washing agent. This research describes a rapid, efficient, and environmentally friendly method for remediation of lead-contaminated soil.

Effect of Choline-Based Deep Eutectic Solvent Pretreatment on the Structure of Cellulose and Lignin in Bagasse

Deep eutectic solvents (DESs) is a newly developed green solvent with low cost, easy preparation and regeneration. Because of its excellent solubility and swelling effect in lignocellulose, it has received widespread attention and recognition. In this study, choline-based deep eutectic solvents (DESs)—choline chloride-urea (CC-U), choline chloride-ethylene glycol (CC-EG), choline chloride-glycerol (CC-G), choline chloride-lactic acid (CC-LA), and choline chloride-oxalic acid (CC-OA)—were used to extract and separate bagasse. The effects of hydrogen bond donors on lignin separation and the fiber and lignin structure were investigated. All five DESs could dissolve lignin from bagasse; acidic DESs exhibited higher solubility than basic DESs. CC-OA effectively separated lignin and hemicellulose. CC-LA showed weaker lignin separation ability than CC-OA. CC-G, CC-EG, and CC-U were more inclined to selectively separate lignin than hemicellulose. The crystalline cellulose II structure was retained after DES pretreatment. Acidic DESs effectively improved the crystallinity of bagasse fiber; the crystallinities for CC-OA and CC-LA pretreatment were 62.26% and 61.65%, respectively. The lignin dissolved in DES was mainly syringyl lignin. The lignin dissolved in CC-U, CC-LA, and CC-OA contained a small amount of guaiacyl lignin.

Choline-Based Deep Eutectic Solvent and Microwave Irradiation as Tools for PET Identification in Blend Fabric

A new, rapid, and eco-friendly technique for identification of polyethylene terephthalate (PET) composition in blend fabric was developed. This technique could replace a conventional composition identification of PET using toxic chemicals such as halogenated organic solvent or strong inorganic acid. Choline-based deep eutectic solvents (DES), such as ethylene glycol- choline chloride, were used as a treatment medium under microwave irradiation. The PET portion of the blend fabrics, such as 65/35 and 50/50 PET/cotton was completely removed by DES containing 5% NaOH (w/v) after 100–140 s of microwave irradiation. Various instrumental analyses confirmed the removal of PET. Finally, a commercial sample was also tested as a practical application of the new test method.

Significant Increase in the Solubility of Celecoxib in Presence of Some Deep Eutectic Solvents as Novel Sustainable Solvents and the Thermodynamic Analysis of These Systems

Background: Deep eutectic solvents (DESs) exist a wide variety of potential and existing applications. Based on the fact that the choline chloride (ChCl) is a complex B vitamin and widely used as food additive, the choline-based DESs are generically regarded as being harmless and non-toxic. In this regard, the low aqueous solubility of celecoxib (CLX) have been increased by use of DESs as neoteric class of solvents at T = (298.15 to 313.15) K. Methods: DESs were prepared by combination of the ChCl/EG, U and G with the molar ratios: 1:2 and ChCl/MA with 1:1. The shake flask method was used to measure the solubility of CLX in the aqueous DESs solutions at different temperatures. Results: The solubility of the CLX increased with increasing the weight fraction of DESs. The observed solubility data was subjected to evaluate the relative performance of a number of models including Apelblat, Yalkowsky and Jouyban–Acree models for their correlation efficacy. Moreover, the apparent dissolution enthalpy, entropy and Gibbs free energy were obtained from the experimental solubility values. Conclusion: It was found that the solubility data was satisfactorily fitted using the mentioned models at different temperatures. The dissolution process of CLX in the studied solvent mixtures within investigated temperature range was endothermic, and the driving mechanism is the positive entropy.

Molecular kinetic extraction mechanism analysis of 1-butanol from n-heptane-1-butanol by choline-based DESs as extractants

Deep eutectic solvent (DES) is considered as a new generation of green solvent due to its advantages such as simple preparation, low price and easy to degrade. In this work, the extraction mechanism of 1-butanol separation from alkanol azeotropic system using choline-based DES was studied. The extraction process was repeated by molecular dynamics(MD) simulation. According to MD simulation results, the nonbonded interaction energies, radial distribution functions, spatial distribution functions and self-diffusion coefficient between different DES and different components were calculated and compared. The results showed that ChCl (choline chloride)/urea (1:2) was one of the four DESs with the best extraction effect, which was very consistent with the experimental results. Through the further analysis of the simulation results, it was found that the hydrogen bond donor in DES had great influence on its extraction efficiency. For the same kind of DES, anion played a dominant role in the extraction of 1-butanol. This work provided some theoretical guidance for the recovery of 1-butanol and the use of choline-based DES, and supplied some reference for the screening of DES.

Magnetic Polydopamine Modified with Choline-Based Deep Eutectic Solvent for the Magnetic Solid-Phase Extraction of Sulfonylurea Herbicides in Water Samples.

A novel magnetic solid-phase extraction technique coupled to ultraperformance liquid chromatography has been developed for separation and preconcentration of four sulfonylurea herbicides (sulfosulfuron, bensulfuron-methyl, pyrazosulfuron-ethyl and halosulfuro-methyl) in aqueous samples. The key point of this method was the application of a novel magnetic nanomaterial that composed of a low eutectic solvent as a shell coated on the magnetic core modified by polydopamine. The extensive active sites outside the low eutectic solvent can effectively adsorb the target herbicide in the extraction process. The obtained magnetic adsorbent was characterized with fourier transform infrared spectrometry, scanning electron microscopy and vibrating sample magnetometer. The influence parameters relevant to this method were optimized. Under the optimum conditions, good linearities could be obtained within the range of 1.0-200μgL-1 for all analytes, with correlation coefficients ≥0.9908. The limit of detections of the method was between 0.0074 and 0.0100μgL-1 and the relative standard deviations were 1.1-3.6%. The enrichment factor is 66.6. In the final experiment, the proposed method was successfully applied to the analysis of sulfonylurea herbicides residue in environment and drinking-water samples, and the obtained recoveries were between 70.6% and 109.4%.

Molecular Mechanism, Thermoeconomic, and Environmental Impact for Separation of Isopropanol and Water Using the Choline-Based DESs as Extractants

Deep eutectic solvents (DESs), as potential green solvents, can be used for the separation of the low-carbon alcohol azeotrope, which has become one of the hot spots in solvent research in recent y...

Enhancement of Lignin Extraction of Poplar by Treatment of Deep Eutectic Solvent with Low Halogen Content.

A novel choline-based deep eutectic solvent (DES) with low halogen content—namely choline lactate-lactic acid (CLL)—was synthesized by replacing the chloride anion with lactate anion in choline chloride-lactic acid (CCL). CLL and CCL treatments were conducted at 140 °C for 12 h with hydrogen bond acceptor/hydrogen bond donor =1/10, thereafter composition analysis and characterizations of the lignin extracted by DES treatment (DES lignin) and the solid residue were carried out. The proposed low halogen content DES presented an improved lignin extraction efficiency. The CLL treatment extracted 90.13% of initial lignin from poplar, while CCL extracted 86.02%. In addition, the CLL treatment also provided DES lignin with an improved purity (91.17%), lower molecular weight (Mw/Mn=1805/971 g/mol) and more concentrated distribution (polydispersity index=1.86). The efficient lignin extraction was mainly ascribed to the cleavage of β-O-4 bonds in lignin macromolecule, especially in the guaiacyl units, thereby breaking them into smaller molecules, facilitating the lignin extraction. The replacement of chloride anion allowed CLL acting as a more efficient DES to interact with lignin macromolecules, thus providing lignin with higher uniformity and suitable molecular weight. The low halogen content DES system proposed in present work could benefit the fractionation of biomass, improve the valorization of lignin compounds and facilitate industrial process in the downstream.

Liquefying Compounds by Forming Deep Eutectic Solvents: A Case Study for Organic Acids and Alcohols.

The criterion to distinguish a simple eutectic mixture from a deep eutectic solvent (DES) lies in the deviations to thermodynamic ideality presented by the components in the system. In this work, the current knowledge of the molecular interactions in types III and V DES is explored to liquefy a set of three fatty acids and three fatty alcohols, here used as model compounds for carboxyl and hydroxyl containing solid compounds. This work shows that thymol, a stronger than usual hydrogen bond donor, is able to form deep eutectic solvents of type V with the fatty alcohols studied. This is particularly interesting, since these DES formed are hydrophobic. Regarding type III DES, the results suggest that the prototypical DES hydrogen bond acceptor, cholinium chloride, is unable to induce negative deviations to ideality in the model molecules studied. By substituting choline with tetramethylammonium chloride, it is shown that the choline hydroxyl group is responsible for the difficulty in forming choline-based deep eutectic solvents and that its absence induces strong negative deviations to ideality in the alkylammonium side. Finally, it is demonstrated that tetrabutylammonium chloride acts as a chloride donning agent, causing significant negative deviations to ideality in both fatty acids and alcohols and leading to the formation of deep eutectic solvents of type III.

Recoverable deep eutectic solvent-based aniline organic pollutant separation technology using choline salt as adsorbent

Removing aniline pollutants from organic waste-liquid rapidly and effectively has become an environmental problem owing to the high toxicity of aniline. Traditional aniline-separation methods have been limited by the complex techniques and high economic cost. In this study, green renewable Choline chloride (choline-salt, [N1,1,1C2OH]Cl) were used as new adsorbents for the removal of aniline by forming choline-based deep eutectic solvents (Choline-DESs) and displayed an excellent aniline removal efficiency. The mechanism of this separation technique is to remove aniline by forming a choline salt-aniline DES. The efficiency of [N1,1,1C2OH]Cl in removing aniline after regeneration and reuse five times was maintained. The adsorption capacity of [N1,1,1C2OH]Cl for aniline was observed at different temperatures (25–50 °C) and the adsorption process was spontaneous and endothermic. The amount of aniline adsorption was modelled by the adsorption isotherm and thermodynamics. The Freundlich model showed that the adsorption mechanism between aniline and choline-salt is controlled by entropy rather than a change in enthalpy. The data indicated that the Choline-DESs have much higher adsorption capacity (>278.5 mg/g) than conventional adsorbents. The high adsorption capacity, simple synthesis technique, and excellent reusability make choline-salt an attractive adsorbent for the removal of aniline from organic waste-liquid.