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Deep Eutectic Solvents: Properties and Applications as Green Solvents

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A special issue of Molecules (ISSN 1420-3049). This special issue belongs to the section "Applied Chemistry".

Deadline for manuscript submissions: closed (31 May 2024) | Viewed by 29917

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Dr. Dorota Warmińska

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Department of Physical Chemistry, Faculty of Chemistry, Gdańsk University of Technology, 80-233 Gdansk, Poland
Interests: green chemistry; ionic liquids; deep eutectic solvents; physicochemical properties; thermodynamic investigation; molecular interactions
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Dr. Iwona Cichowska-Kopczyńska

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Department of Process Engineering and Chemical Technology, Faculty of Chemistry, Gdańsk University of Technology, 80-233 Gdansk, Poland
Interests: ionic liquids; deep eutectic solvents; mass transfer; membrane processes; physicochemical properties; gas separation; sustainable technologies
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Dr. Grzegorz Boczkaj

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Department of Sanitary Engineering, Faculty of Civil and Environmental Engineering, Gdansk University of Technology, 80-233 Gdansk, Poland
Interests: environmental remediation; advanced oxidation process; wastewater treatment; deep eutectic solvents
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Special Issue Information

Dear Colleagues,

For two decades, deep eutectic solvents (DES) have been competing with ionic liquids due to lower production costs, lower toxicity, and favorable biodegradability. Many studies have demonstrated their usefulness in a wide range of applications, including extraction, separation, and catalysis, in the pharmaceutical industry, depending on the physicochemical properties of DES. Therefore, the Special Issue “Deep Eutectic Solvents: Properties and Applications as Green Solvents” is devoted to the collection of up-to-date original and review papers in this field. In the original articles, both experimental and computational research on pure DES and their mixtures with other solvents are welcome.

Dr. Dorota Warmińska
Dr. Iwona Cichowska-Kopczyńska
Dr. Grzegorz Boczkaj
Guest Editors

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Keywords

eutectic solvents
natural deep eutectic solvents
therapeutic deep eutectic solvents
physicochemical and thermodynamic properties
extraction and separation
catalysis
organic synthesis
drug delivery

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Published Papers (11 papers)

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Research

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16 pages, 1997 KiB

Open AccessArticle

Zinc and Lead Leaching from Sphalerite–Galena Concentrate Using Deep Eutectic Solvents Based on Choline Chloride: Effect of Roasting and Iodine as Oxidizing Agent

by Katherine Moreno, Ximena Díaz, Diana Endara, Fernando Sánchez and Carlos F. Aragón-Tobar

Molecules 2024, 29(16), 3742; https://doi.org/10.3390/molecules29163742 - 7 Aug 2024

Viewed by 839

Abstract

The traditional metallurgical routes for producing lead and zinc from primary sources have a significant environmental footprint. Thus, using less pollutant solvents, such as deep eutectic solvents (DESs), would offer a greener solution in metal extraction. This study explores the use of three DESs based on choline chloride (ChCl) (1:2 ChCl–urea, 1:2 ChCl–ethylene glycol, and 1:2 ChCl–glycerol) for recovering Zn and Pb from a sphalerite–galena concentrate of the mining region in Ecuador. Leaching tests of the concentrate (untreated and roasted at 600 °C) in each DES were conducted (30 °C—24 h). The effect of adding iodine as an oxidizing agent was also evaluated. Recoveries of 2% (Zn) and 14% (Pb) were reported when leaching the untreated concentrate with DES. These recovery values increased to 11% (Zn) and 99% (Pb) after adding iodine during the leaching of the untreated concentrate. Roasting had a similar effect on leaching, increasing the recovery values of Zn (75%) and Pb (90%). Combining roasting as a pretreatment and iodine as an oxidizing agent produced higher Zn recoveries (99%) and Pb (99%). These results were compared to recoveries in acid leaching (H₂SO₄ and HNO₃), revealing the potential of DESs as an alternative for metal recovery from primary sources. Full article

(This article belongs to the Special Issue Deep Eutectic Solvents: Properties and Applications as Green Solvents)

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12 pages, 4847 KiB

Open AccessArticle

The Antisolvent Precipitation of CuZnOx Mixed Oxide Materials Using a Choline Chloride-Urea Deep Eutectic Solvent

by William T. Wallace, James S. Hayward, Amy R. Marsh and Jonathan K. Bartley

Molecules 2024, 29(14), 3357; https://doi.org/10.3390/molecules29143357 - 17 Jul 2024

Cited by 1 | Viewed by 805

Abstract

Metal oxides have applications in a variety of different fields, and new synthesis methods are needed to control their properties and improve their performance as functional materials. In this study, we investigated a low-cost antisolvent precipitation method using a choline chloride-urea deep eutectic solvent to precipitate CuZnOx materials using water as the antisolvent. Using this methodology, the metal oxide materials can be precipitated directly from the deep eutectic solvent without the need for a high-temperature calcination step that can lead to a reduction in defects and surface area, which are important properties in applications such as catalysis. Full article

(This article belongs to the Special Issue Deep Eutectic Solvents: Properties and Applications as Green Solvents)

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15 pages, 1439 KiB

Open AccessArticle

Mineral Acid Co-Extraction in Reactive Extraction of Lactic Acid Using a Thymol-Menthol Deep Eutectic Solvent as a Green Modifier

by Paul Demmelmayer, Marija Ćosić and Marlene Kienberger

Molecules 2024, 29(8), 1722; https://doi.org/10.3390/molecules29081722 - 11 Apr 2024

Cited by 1 | Viewed by 1278

Abstract

Carboxylic acids can be isolated from fermentation broths using reactive liquid-liquid extraction, offering an alternative to the environmentally harmful state-of-the-art process of precipitating calcium lactate. To enhance the sustainability of liquid-liquid extraction processes, greener solvents, such as natural deep eutectic solvents, are investigated. However, fermentation broths often exhibit pH values unsuitable for carboxylic acid extraction, which can be adjusted using mineral acids, though mineral acids may be co-extracted. In this study, we systematically examine the co-extraction of hydrochloric, nitric, sulfuric, and phosphoric acid during extraction and back-extraction of lactic acid. The solvent phase consisted of tri-n-octylamine, trioctylphosphine oxide, or tributyl phosphate diluted in a thymol-menthol deep eutectic solvent. The back-extraction was conducted using a diluent swing with p-cymene as the antisolvent and water as the receiving phase. Tri-n-octylamine showed the highest efficiency for lactic acid (up to 29.8%) but also the highest co-extraction of mineral acids (up to 50.9%). In contrast, trioctylphosphine oxide exhibited a lower but more selective lactic acid extraction (5.94%) with low mineral acids co-extraction (0.135%). Overall, the highest co-extraction was observed for phosphoric acid and the lowest for nitric acid. In conclusion, the selected solvent phase composition and mineral acid influence the co-extraction and, thus, final product purity. The successful application of the natural deep eutectic solvent as the modifier enhances the sustainability of liquid–liquid extraction processes. Full article

(This article belongs to the Special Issue Deep Eutectic Solvents: Properties and Applications as Green Solvents)

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16 pages, 3678 KiB

Open AccessArticle

Recovery of Residual Lead from Automotive Battery Recycling Slag Using Deep Eutectic Solvents

by Bruna Salgado, Diana Endara, Carlos F. Aragón-Tobar, Ernesto de la Torre and Luis Ullauri

Molecules 2024, 29(2), 394; https://doi.org/10.3390/molecules29020394 - 13 Jan 2024

Cited by 1 | Viewed by 1712

Abstract

In this study, we address the ecological challenges posed by automotive battery recycling, a process notorious for its environmental impact due to the buildup of hazardous waste like foundry slag. We propose a relatively cheap and safe solution for lead removal and recovery from samples of this type of slag. The analysis of TCLP extracts revealed non-compliance with international regulations, showing lead concentrations of up to 5.4% primarily in the form of anglesite (PbSO₄), as detected by XRF/XRD. We employed deep eutectic solvents (DES) as leaching agents known for their biodegradability and safety in hydrometallurgical processing. Five operational variables were systematically evaluated: sample type, solvent, concentration, temperature, and time. Using a solvent composed of choline chloride and glycerin in a 2:1 molar ratio, we achieved 95% lead dissolution from acidic samples at 90 °C, with agitation at 470 rpm, a pulp concentration of 5%, and a 5 h duration. Furthermore, we successfully recovered 55% of the lead in an optimized solution using an electrowinning cell. This research demonstrates the ability of DES to decontaminate slag, enabling compliance with regulations, the recovery of valuable metals, and new possibilities for the remaining material. Full article

(This article belongs to the Special Issue Deep Eutectic Solvents: Properties and Applications as Green Solvents)

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15 pages, 2038 KiB

Open AccessArticle

Dissolution of Metals (Cu, Fe, Pb, and Zn) from Different Metal-Bearing Species (Sulfides, Oxides, and Sulfates) Using Three Deep Eutectic Solvents Based on Choline Chloride

by Carlos F. Aragón-Tobar, Diana Endara and Ernesto de la Torre

Molecules 2024, 29(2), 290; https://doi.org/10.3390/molecules29020290 - 5 Jan 2024

Cited by 3 | Viewed by 2000

Abstract

Nowadays, deep eutectic solvents (DESs) are seen as environmentally friendly alternatives with the potential to replace traditional solvents used in hydrometallurgical processes. Although DESs have been successfully applied in the recovery of metals from secondary sources, there is still innovative potential regarding DESs as green leaching agents applied in the recovery of metals from primary sources like polysulfide ores. This study aimed to evaluate the characteristics of DESs as solvents for some of the main metals present in typical polymetallic concentrates, like Cu, Fe, Pb, and Zn. Thus, three DESs based on choline chloride (ChCl) were prepared: 1:2 ChCl-urea (also known as reline), 1:2 ChCl-ethylene glycol (also known as ethaline), and 1:2 ChCl-glycerol (also known as glyceline). Then, dissolution tests at 30 °C were carried out with these DESs and different metal- (Cu, Fe, Pb, and Zn) bearing compounds (sulfates, oxides, and sulfides). According to the dissolution tests, it was found that the solubility of the studied metals (expressed as g of metal per Kg of DES) was dictated by the bearing species, reaching the dissolution of the metals from sulfates with values as high as two orders of magnitude higher than the metal solubility values for metal oxides and sulfides. Full article

(This article belongs to the Special Issue Deep Eutectic Solvents: Properties and Applications as Green Solvents)

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24 pages, 7328 KiB

Open AccessArticle

Intermolecular Interactions of Edaravone in Aqueous Solutions of Ethaline and Glyceline Inferred from Experiments and Quantum Chemistry Computations

by Piotr Cysewski, Tomasz Jeliński and Maciej Przybyłek

Molecules 2023, 28(2), 629; https://doi.org/10.3390/molecules28020629 - 7 Jan 2023

Cited by 9 | Viewed by 2486

Abstract

Edaravone, acting as a cerebral protective agent, is administered to treat acute brain infarction. Its poor solubility is addressed here by means of optimizing the composition of the aqueous choline chloride (ChCl)-based eutectic solvents prepared with ethylene glycol (EG) or glycerol (GL) in the three different designed solvents compositions. The slurry method was used for spectroscopic solubility determination in temperatures between 298.15 K and 313.15 K. Measurements confirmed that ethaline (ETA = ChCl:EG = 1:2) and glyceline (GLE = ChCl:GL = 1:2) are very effective solvents for edaravone. The solubility at 298.15 K in the optimal compositions was found to be equal x_E = 0.158 (c_E = 302.96 mg/mL) and x_E = 0.105 (c_E = 191.06 mg/mL) for glyceline and ethaline, respectively. In addition, it was documented that wetting of neat eutectic mixtures increases edaravone solubility which is a fortunate circumstance not only from the perspective of a solubility advantage but also addresses high hygroscopicity of eutectic mixtures. The aqueous mixture with 0.6 mole fraction of the optimal composition yielded solubility values at 298.15 K equal to x_E = 0.193 (c_E = 459.69 mg/mL) and x_E = 0.145 (c_E = 344.22 mg/mL) for glyceline and ethaline, respectively. Since GLE is a pharmaceutically acceptable solvent, it is possible to consider this as a potential new liquid form of this drug with a tunable dosage. In fact, the recommended amount of edaravone administered to patients can be easily achieved using the studied systems. The observed high solubility is interpreted in terms of intermolecular interactions computed using the Conductor-like Screening Model for Real Solvents (COSMO-RS) approach and corrected for accounting of electron correlation, zero-point vibrational energy and basis set superposition errors. Extensive conformational search allowed for identifying the most probable contacts, the thermodynamic and geometric features of which were collected and discussed. It was documented that edaravone can form stable dimers stabilized via stacking interactions between five-membered heterocyclic rings. In addition, edaravone can act as a hydrogen bond acceptor with all components of the studied systems with the highest affinities to ion pairs of ETA and GLE. Finally, the linear regression model was formulated, which can accurately estimate edaravone solubility utilizing molecular descriptors obtained from COSMO-RS computations. This enables the screening of new eutectic solvents for finding greener replacers of designed solvents. The theoretical analysis of tautomeric equilibria confirmed that keto-isomer edaravone is predominant in the bulk liquid phase of all considered deep eutectic solvents (DES). Full article

(This article belongs to the Special Issue Deep Eutectic Solvents: Properties and Applications as Green Solvents)

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16 pages, 3265 KiB

Open AccessArticle

Ultrasonic-Assisted Efficient Extraction of Coumarins from Peucedanum decursivum (Miq.) Maxim Using Deep Eutectic Solvents Combined with an Enzyme Pretreatment

by Zeyu Li and Qian Li

Molecules 2022, 27(17), 5715; https://doi.org/10.3390/molecules27175715 - 5 Sep 2022

Cited by 5 | Viewed by 2275

Abstract

In this study, the ultrasonic-assisted extraction of total coumarins from Peucedanum decursivum (Miq.) Maxim (P. decursivum) via the combination of deep eutectic solvents (DESs) with cellulase pretreatment was carried out. Among the 15 kinds of DESs with choline chloride as hydrogen bond acceptors, the DES system of choline chloride/1,4-butanediol with a molar ratio of 1:4 showed the best extraction effect. First, single-factor experiments were performed using the following factors: liquid–solid ratio, pH, enzyme dosage and ultrasonic temperature. The Box–Behnken design (BBD) and response surface methodology (RSM) were employed to optimize the extraction conditions and obtain the following optimal parameter values for the extraction of coumarins from P. decursivum: liquid–solid ratio 14:1 mL/g, pH 5.0, enzyme dosage 0.2%, ultrasonic temperature 60 °C and ultrasonic time 50 min. Under these conditions, the extraction yield of total coumarins from P. decursivum could reach 2.65%, which was close to the predicted extraction yield of 2.68%. Furthermore, the contents of six coumarins, namely, umbelliferone, nodakenin, xanthotoxin, bergapten, imperatorin and decursin were determined to be 0.707 mg·g⁻¹, 0.085 mg·g⁻¹, 1.651 mg·g⁻¹, 2.806 mg·g⁻¹, 0.570 mg·g⁻¹ and 0.449 mg·g⁻¹, respectively, using HPLC-MS after the optimization. In addition, the cell fragmentation of P. decursivum powder obtained using ultrasonic-assisted DES extraction with enzyme pretreatment was found to be the most comprehensive using scanning electron microscopy (SEM), which indicated the highest extraction efficiency for P. decursivum. Finally, the in vitro antioxidant activity of the extracts was evaluated via radical scavenging with 1,1-diphenyl-2-picrylhydrazyl (DPPH), which showed that ultrasonic-assisted DES extraction with enzyme pretreatment exhibited significant antioxidant activity with DPPH radical scavenging of up to 97.90%. This work developed a new and efficient extraction method for coumarins. Full article

(This article belongs to the Special Issue Deep Eutectic Solvents: Properties and Applications as Green Solvents)

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14 pages, 1862 KiB

Open AccessArticle

Lactic Acid-Based Natural Deep Eutectic Solvents to Extract Bioactives from Marine By-Products

by Maha M. Abdallah, Martim Cardeira, Ana A. Matias, Maria Rosário Bronze and Naiara Fernández

Molecules 2022, 27(14), 4356; https://doi.org/10.3390/molecules27144356 - 7 Jul 2022

Cited by 13 | Viewed by 3341

Abstract

Natural deep eutectic solvents (NaDES) were used to extract bioactive compounds from marine by-products: codfish bones, mussel meat, and tuna vitreous humor. NaDES were prepared using natural compounds, including lactic acid (Lac), fructose (Fru), and urea (Ur), and were characterized to define their physicochemical properties, including the viscosity, density, surface tension, and refractive index. FTIR and NMR analysis confirmed the presence of intermolecular hydrogen bonding in NaDES. The extracts obtained using these NaDES were characterized to define their composition. Results demonstrated that the extract’s composition differed highly, depending not only on the DES used, but also on the structure and composition of the raw material. Proteins and lipids were mainly present in extracts obtained from mussels, while ash content was highest in the extracts obtained from codfish bones. The biocompatibility of NaDES and the soluble fractions (SF) of the raw materials in NaDES was evaluated, and it was possible to conclude that the soluble ingredients obtained from the raw materials improved the biocompatibility of NaDES. Full article

(This article belongs to the Special Issue Deep Eutectic Solvents: Properties and Applications as Green Solvents)

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9 pages, 1609 KiB

Open AccessArticle

New Simple and Robust Method for Determination of Polarity of Deep Eutectic Solvents (DESs) by Means of Contact Angle Measurement

by Łukasz Cichocki, Dorota Warmińska, Justyna Łuczak, Andrzej Przyjazny and Grzegorz Boczkaj

Molecules 2022, 27(13), 4198; https://doi.org/10.3390/molecules27134198 - 29 Jun 2022

Cited by 10 | Viewed by 2731

Abstract

The paper presents a new method for evaluating the polarity and hydrophobicity of deep eutectic solvents (DESs) based on the measurement of the DES contact angle on glass. DESs consisting of benzoic acid derivatives and quaternary ammonium chlorides–tetrabutylammonium chloride (TBAC) and benzyldimethylhexadecylammonium chloride [...] Read more.

E_{T} (30)

solvatochromic scale based on Reichardt’s dye were used. The research demonstrated the high accuracy and precision of the developed procedure. The simplicity of the examination and the availability of basic equipment allow for the implementation of the developed method in routine investigations of DESs. Full article

(This article belongs to the Special Issue Deep Eutectic Solvents: Properties and Applications as Green Solvents)

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Review

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14 pages, 3536 KiB

Open AccessReview

A Review on the Use of Deep Eutectic Solvents in Protection Reactions

by Rosa Scarpelli, Renata Bence, Natividad Carolina Herrera Cano, Antonio Procopio, Daniel Wunderlin and Monica Nardi

Molecules 2024, 29(4), 818; https://doi.org/10.3390/molecules29040818 - 10 Feb 2024

Cited by 4 | Viewed by 2714

Abstract

Given the recent research on the application of eco-sustainable methods in organic chemistry, we have focused our attention on the derivatization processes for fundamental functional groups in organic chemistry, such as amino, hydroxyl and carbonyl groups. Protection reactions are needed to temporarily block a certain reactive site on a molecule. The use of green solvents in this context has made an excellent contribution to the development of eco-sustainable methods. In recent years, deep eutectic solvents (DESs) have had great success as a new class of green solvents used in various chemical applications, such as extraction or synthetic processes. These solvents are biodegradable and nontoxic. In this framework, a list of relevant works found in the literature is described, considering DESs to be a good alternative to classic toxic solvents in the protection reactions of important functional groups. Full article

(This article belongs to the Special Issue Deep Eutectic Solvents: Properties and Applications as Green Solvents)

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30 pages, 1381 KiB

Open AccessReview

Deep Eutectic Solvents: Properties and Applications in CO₂ Separation

by Iwona Cichowska-Kopczyńska, Bartosz Nowosielski and Dorota Warmińska

Molecules 2023, 28(14), 5293; https://doi.org/10.3390/molecules28145293 - 8 Jul 2023

Cited by 30 | Viewed by 7733

Abstract

Nowadays, many researchers are focused on finding a solution to the problem of global warming. Carbon dioxide is considered to be responsible for the “greenhouse” effect. The largest global emission of industrial CO₂ comes from fossil fuel combustion, which makes power plants the perfect point source targets for immediate CO₂ emission reductions. A state-of-the-art method for capturing carbon dioxide is chemical absorption using an aqueous solution of alkanolamines, most frequently a 30% wt. solution of monoethanolamine (MEA). Unfortunately, the usage of alkanolamines has a number of drawbacks, such as the corrosive nature of the reaction environment, the loss of the solvent due to its volatility, and a high energy demand at the regeneration step. These problems have driven the search for alternatives to that method, and deep eutectic solvents (DESs) might be a very good substitute. Many types of DESs have thus far been investigated for efficient CO₂ capture, and various hydrogen bond donors and acceptors have been used. Deep eutectic solvents that are capable of absorbing carbon dioxide physically and chemically have been reported. Strategies for further CO₂ absorption improvement, such as the addition of water, other co-solvents, or metal salts, have been proposed. Within this review, the physical properties of DESs are presented, and their effects on CO₂ absorption capacity are discussed in conjunction with the types of HBAs and HBDs and their molar ratios. The practical issues of using DESs for CO₂ separation are also described. Full article

(This article belongs to the Special Issue Deep Eutectic Solvents: Properties and Applications as Green Solvents)

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