Deep Eutectic Solvents Components Research Articles

Addressing the Reuse of Deep Eutectic Solvents in Li-ion Battery Recycling: Insights Into Dissolution Mechanism, Metal Recovery, Regeneration and Decomposition.

Deep eutectic solvents (DESs) have garnered attention in Li-ion battery (LIB) recycling due to their declared eco-friendly attributes and adjustable metal dissolution selectivity, offering a promising avenue for recycling processes. However, DESs currently lack competitiveness compared to mineral acids, commonly used in industrial-scale LIB recycling. Current research primarily focuses on optimizing DES formulation and experimental conditions to maximize metal dissolution yields in standalone leaching experiments. While achieving yields comparable to traditional leaching systems is important, extensive DES reuse is vital for overall recycling feasibility. To achieve this, evaluating the metal dissolution mechanism can assist in estimating DES consumption rates and assessing process makeup stream costs. The selection of appropriate metal recovery and DES regeneration strategies is essential to enable subsequent reuse over multiple cycles. Finally, decomposition of DES components should be avoided throughout the designed recycling process, as by-products can impact leaching efficiency and compromise the safety and environmental friendliness of DES. In this review, these aspects are emphasized with the aim of directing research efforts away from simply pursuing the maximization of metal dissolution efficiency, towards a broader view focusing on the application of DES beyond the laboratory scale.

A tandem approach for precipitant-free highly selective recovery of valuable metals from end-of-life lithium-ion batteries using a green deep eutectic solvent

Recently, recycling lithium-ion batteries (LIBs) waste and the efficient recovery of valuable metals has become crucial for the circular economy. Deep eutectic solvents (DESs) have shown immense potential for metal extraction from end-of-life (EoL) LIBs. However, a complicated subsequent separation process is required due to the non-selectivity of the DES components for metal. Herein, we propose a tandem precipitant-free hydrometallurgical process for the selective recovery of Li and other valuable metals (Ni, Co, Mn) from EoL LIBs using a green DES. The process parameters, viz., reaction temperature (T), time (t), pulp density (S/L), and molar ratio (MR) of ethylene glycol to tartaric acid, were optimized via the statistical optimization technique of response surface methodology. The results revealed maximum extraction efficiencies of 99.2±0.5%, 96.1±1.4%, 95.2±1.2%, and 97.8±1.5% for Li, Ni, Co, and Mn, respectively, under the optimized process conditions of T = 118 °C, t = 17 min, S/L = 42 g/L, and MR = 3:1. The kinetic study showed that interfacial reaction governed the extraction process. A plausible mechanism depicting the role of DES constituents in synergistically facilitating the extraction reaction was elucidated. Moreover, Li and other metals (Ni, Co, and Mn) were selectively separated and recovered with an overall efficiency of ∼99%. The reusability of the recovered metal products and the DES were also assessed for a closed-loop recycling process. At the outset, the proposed process paves the way for a greener alternative for recycling valuable metals from EoL LIBs rather than conventional acid-based leaching processes.

Graph neural networks for CO[formula omitted] solubility predictions in Deep Eutectic Solvents

Deep Eutectic Solvents (DESs) are a promising class of solvents for CO2 capture. DESs are complex mixtures that can be designed to optimize CO2 solubility and overall capture process efficiency. However, the vast design landscape of DES mixtures makes experimental investigation prohibitive; as such, there is a need for computational models that can quickly and efficiently navigate the design space and inform data collection efforts. In this work, we propose Graph Neural Network (GNN) models for predicting CO2 solubility for DESs; the GNN leverages a mixture graph representation that captures the molecular structure of the DES components as well as their intermolecular interactions. We compare the GNN framework against alternative architectures (neural networks, graph convolution networks, and random forests) and data representations (molecular fingerprints, sigma profiles, and graphs). We show that the proposed approach offers superior predictive performance; specifically, we show that solubility can be predicted reliably directly from molecular structure (without the need of using sigma profiles as proposed in previous studies). This result is important, as obtaining sigma profiles requires expensive density functional theory computations. We also explored the ability of GNNs to predict solubility for new DES mixtures and operating conditions. We found that the model extrapolates across temperature reliably. However, we also found deficiencies in the ability of the model to predict solubility for DES mixtures, pressures, and molar ratio not included in the training sets; we show that this is due to an inherent lack of chemical diversity in datasets available in the literature. The proposed computational capabilities can thus help navigate the design space of DES and inform data collection efforts. Our models, data, and benchmarks are shared as Python code implemented in Jupyter notebooks.

In situ formation of a deep eutectic solvent for liquid-liquid microextraction of synthetic phenolic antioxidants in edible oil

A simple and ecofriendly liquid-liquid microextraction (LLME) method was developed for the extraction of synthetic phenolic antioxidants (SPAs, e.g. tert-butyl hydroquinone (TBHQ) and butylated hydroxyanisole (BHA)) in edible oil. Compared with time-consuming and cumbersome off-line prepared deep eutectic solvent (DES), the in-situ formulated DES allowed to directly add DES components into sample matrix, making the sample preparation procedure greatly simplified. Preliminary experiment indicated that the DES made of 1:2 (molar ratio) tetrabutylammonium chloride (TBAC) and acetic acid (AA) was suitable for the extraction of SPAs. Under the optimized conditions, by combining with HPLC, the in-situ DES-LLME-HPLC method showed satisfactory detection limits (0.7−1.3 μg/L), precisions (RSDs≤5.0%), enrichment factors (20.8−22.0), recoveries (89.2%–103.6%), and linearity over 5−500 μg/L (TBHQ) and 10−500 μg/L (BHA) (R2 ≥ 0.9991). In addition, the method displayed acceptable matrix effect and robustness. Hence, it is promising for the extraction and determination of SPAs in real edible oil.

Meltable Aluminum Molecular Rings with Fluorescence and Nonlinear Optical Properties.

Crystal-liquid-glass, which combines the tunable properties of crystalline compounds with the processability of glasses, has emerged as a new class of materials for fabricating bulk-shapable devices in real applications. Inspired by the characteristics of deep eutectic solvent (DES) mixtures involving significant depressions in melting points compared to their neat constituent components, in this study, we designed and synthesized the first examples of meltable aluminum oxo clusters (AlOCs) via lattice doping with DESs at the molecular level. The abundant and strong hydrogen bonding between the aluminum molecular ring, DES components, and lattice solvents is postulated to be the root that affords melting point depressions and, thus, "melting" clusters. We prepared a transparent bubble-free glass film under autogenous pressure using a hot-press method. These cluster-based films exhibited luminescent and nonlinear optical properties similar to those of pristine crystalline compounds. Our study belongs to the interdisciplinary disciplines of chemistry and physics. It not only breaks the limitations of crystalline glass on metal and ligand types but also acts as a general guide for extending the range of meltable crystalline materials.

Meltable Aluminum Molecular Rings with Fluorescence and Nonlinear Optical Properties

AbstractCrystal–liquid–glass, which combines the tunable properties of crystalline compounds with the processability of glasses, has emerged as a new class of materials for fabricating bulk‐shapable devices in real applications. Inspired by the characteristics of deep eutectic solvent (DES) mixtures involving significant depressions in melting points compared to their neat constituent components, in this study, we designed and synthesized the first examples of meltable aluminum oxo clusters (AlOCs) via lattice doping with DESs at the molecular level. The abundant and strong hydrogen bonding between the aluminum molecular ring, DES components, and lattice solvents is postulated to be the root that affords melting point depressions and, thus, “melting” clusters. We prepared a transparent bubble‐free glass film under autogenous pressure using a hot‐press method. These cluster‐based films exhibited luminescent and nonlinear optical properties similar to those of pristine crystalline compounds. Our study belongs to the interdisciplinary disciplines of chemistry and physics. It not only breaks the limitations of crystalline glass on metal and ligand types but also acts as a general guide for extending the range of meltable crystalline materials.

Effect of the water content and the lengthening of fatty acids chain on the iCALB‐catalyzed esterification in deep eutectic solvents

AbstractFour Deep Eutectic Solvents (DES) based on choline chloride (ChCl) and different hydrogen bond donors (1,4‐butanediol, glycerol, isosorbide, and urea) were tested as reaction medium for the immobilized Candida antarctica B (iCALB) lipase‐catalyzed esterification of fatty acids with n‐butanol. Although the strong hydrogen bonds between DES components were expected to lower their reactivity, all except urea, competed in the esterification reaction. To study the effect of acyl group donor and water, different chain length of saturated fatty acids (ranging from 6:0 to 18:0) and water content (ranging from 0, 1, 2 or 3 molar ratio of water/ChCl) were tested in the lipase‐catalyzed esterification with n‐butanol in ChCl:urea (1:2, molar ratio). When the incubation was performed in the absence of water, the shorter the fatty acid chain length, the higher the conversion. Upon water addition, a drastic increase in the esterification rate of all the fatty acids was observed and, conversely to what occurred in the anhydrous media, the longer the fatty acid chain length, the higher the conversion. Results suggest that water concentration in the DES medium possesses a multifactorial effect, as it influences the enzyme activity, the solvent viscosity, the DES structure, and the interaction between DES components, substrates, and enzymes, thus determining the efficiency and yield of the esterification reaction.

Molecular dynamics investigation of the interaction between volatile organic compounds and deep eutectic solvents

ABSTRACTMixtures of tetrabutylammonium-chloride-based deep eutectic solvent (DES) and three volatile organic compounds (VOCs) – butanal, ethanol, and toluene – have been investigated using classical molecular dynamics simulations. Various structural analyses like radial and spatial distribution functions reveal the presence of specific interactions between DES components and VOCs. The interaction between the VOC and DES components depends on the nature of the former. Both ethanol and butanal have an H-bond interaction with chloride and ethylene glycol. Tetrabutylammonium cations are present above and below the ring of toluene due to the presence of π electron cloud, and toluene also forms π hydrogen bonds with ethylene glycol. The structure of DES is not significantly affected by the absorption of VOCs, which is reflected in their radial distribution functions. Components of DES become more mobile with the addition of VOCs. The interfacial region was found to be the most favourable location for the presence of VOCs.

Analysis of temperature effect in the CO2 absorption using a deep eutectic solvent: An in silico approach

The excess level of carbon dioxide in the atmosphere has contributed a lot to global warming, occasioning several damages to the planet. Therefore, it is urgent to find ways to capture this gas. Then, the present work analyzed the temperature effect in CO2 absorption through deep eutectic solvents (DESs) based on urea and choline chloride using an in silico approach. The Molecular Dynamics (MD) simulations indicated that the increased temperature reduced the interaction potential of carbon dioxide molecules with the DESs components, indicating that the absorption process is more favorable at 303 K. On the other hand, the Noncovalent Interactions (NCI) simulations suggest that the increased temperature reduced the strong attractions and increased repulsive interactions between the carbon dioxide molecules with the solvent analyzed. Therefore, both in silico approaches suggest that the carbon dioxide absorption is more indicated at 303 K.

Deep eutectic solvents combined with beta-cyclodextrin derivatives for chiral separation of typical adrenergic receptor agonists by capillary electrophoresis with amperometric detection

Enantioseparation has always been one of the research hotspots and difficulties in the field of modern separation science. In this work, a binary chiral electrophoretic separation system was constructed using deep eutectic solvents (DESs) coupled with beta-cyclodextrin derivatives based on capillary electrophoresis with amperometric detection system, and five groups of typical adrenergic receptor agonists (adrenaline, salbutamol, isoproterenol, norepinephrine and terbutaline) were selected as the model enantiomers. The effects of additive types and contents of DESs and cyclodextrins, and the pH value and concentration of the running buffer on the resolution of the selected chiral compounds were investigated in detail. The mechanism of DESs improving separation was explored preliminarily by means of UV spectrophotometry, which was further verified based on the comparison of single and mixed components of choline chlorine-urea DES. Under the optimum conditions, the relative standard deviations for inter-day and intra-day repeatability of the migration time, peak area and resolution for adrenaline and salbutamol were within 8.7%, and the limits of detection reached 0.030 μg mL−1 (S/N = 3). The recovery data were in the range of 96.3–118.7%. The developed methods have been applied for the analyses of (+)-adrenaline hydrochloride injection and (±)-salbutamol aerosol. This binary chiral electrophoretic separation system by CE-AD has high detection sensitivity and low analytical cost, providing an alternative for the separation and analysis of chiral drugs.

Solvometallurgical recycling of spent LiNixCoyMnzO2 (NCM) cathode material using ternary choline chloride-ethylene glycol-p-toluenesulfonic acid deep eutectic solvent

In recent years, recycling lithium-ion batteries (LIBs) has become imperative considering their growing demand will soon lead to massive disposal of spent LIBs which causes critical environmental problems. In this study, solvometallurgy using deep eutectic solvents (DESs) is used to efficiently recover valuable metals from spent LIBs. The potential of different types of DES (binary and ternary) to leach LIB samples is evaluated. Initial leaching tests demonstrate that p-toluenesulfonic acid (PTSA) -based DES results in high metal extraction at 100 °C with 10 g/L pulp density and 72 h residence time. Cyclic voltammetry indicates a high current density of PTSA, a strong leaching agent in the DES structure. A ternary DES containing choline chloride, ethylene glycol, and p-toluenesulfonic acid (ChCl-EG-PTSA) show better performance as a leachant than other DESs. The formation of hydrogen bonds between p-toluenesulfonic acid-based DES components is examined by Fourier transform infrared spectroscopy and proton nuclear magnetic resonance. This study provides a new ternary DES for solvometallurgical recycling of LIBs while considering principles for sustainable development.

Supercritical CO2/Deep Eutectic Solvent Biphasic System as a New Green and Sustainable Solvent System for Different Applications: Insights from Molecular Dynamics Simulations.

Deep eutectic solvents (DESs) are one of the most interesting research subjects in green chemistry nowadays. Due to their low toxicity, simple synthesis, and lower prices, they have gradually taken the place of other green solvents such as ionic liquids (ILs) in sustainable processes. However, problems such as high viscosity and high polarity limit the applications of DESs in areas such as extraction, catalysis, and biocatalysis. In this work, we introduce and evaluate the potential application of scCO2/DES for the first time. Molecular dynamics simulations were used to examine the phase behavior, polarity, molecular mobilities, and microstructure of this system. Results show that CO2 molecules can significantly diffuse to the DES phase, while DES components do not appear in the scCO2 phase. The diffused CO2 molecules significantly enhanced the molecular mobility of the DES components. The presence of CO2 molecules changes the DES polarity so that hexane can be solubilized and dispersed in the DES phase. Radial distribution functions show that the solubilized CO2 molecules have negligible effects on the microstructure of DES. It was shown that chloride and urea are the main interaction sites of CO2 in DES. The results of this study show that scCO2/DES as a new class of green and versatile solvents can open a new promising window for research in sustainable chemistry and engineering.

Intermolecular interactions induced property improvement for clean fracturing fluid by deep eutectic solvents

Fracturing fluid property play a critical role in developing unconventional reservoirs. Deep eutectic solvents (DESs) show fascinating potential for property improvement of clean fracturing fluids (CFFs) due to their low-price, low-toxicity, chemical stability and flexible designability. In this work, DESs were synthesized by mixing hydrogen bond acceptors (HBAs) and a given hydrogen bond donor (HBD) to explore their underlying influence on CFF properties based on the intermolecular interactions. The hydrogen-bonding, van der Waals and electrostatic interactions between DES components and surfactants improved the CFF properties by promoting the arrangement of surfactants at interface and enhancing the micelle network strength. The HBD enhanced the resistance of CFF for Ca2+ due to coordination-bonding interaction. The DESs composed of choline chloride (ChCl) and malonic acid show great enhancement for surface, rheology, temperature resistance, salt tolerance, drag reduction, and gel-breaking performance of CFFs. The DESs also improved the gel-breaking CFF-oil interactions, increasing the imbibition efficiencies to 44.2% in 74 h. Adjusting HBAs can effectively strengthen the intermolecular interactions (e.g., HBA-surfactant and HBD-surfactant interactions) to improve CFF properties. The DESs developed in this study provide a novel strategy to intensify CFF properties.

Determination of the solubility profile of isophthalic acid in some aqueous solutions of betaine-based deep eutectic solvents: Study the extent of H-bonding interactions between starting materials of deep eutectic solvents in aqueous medium

The equilibrium solubility of isophthalic acid (IPA) in three aqueous solutions of betaine/propylene glycol (Bet/PG, 1:5 M ratio), betaine/ethylene glycol (Bet/EG, 1:3 M ratio) and betaine/glycerol (Bet/Gly, 1:3 M ratio) deep eutectic solvents (DESs) (1) was determined experimentally by utilizing a shake-flask method at 293.15–313.15 K covering the whole composition range at atmospheric pressure (≈85 kPa). For three investigated systems, an increase in solubility was observed by decreasing water mass fraction; so that, the lowest and highest solubilities were in water at 293.15 K and pure DESs at 323.15 K, respectively. Also, the mixtures containing PG presented the higher values of the solubility than that of EG or Gly which may be attributed to its lower dipole moment and dielectric constant (2.27 D, 32.0) than the others. By representation the derived equilibrium solubilities with models of Jouyban-Acree, Jouyban-Acree-van't Hoff, NRTL and Wilson a maximum overall mean relative deviation of 15.9% was achieved. Moreover, the solubilities of IPA in ternary (Bet + PG, EG or Gly + water) mixtures at 298.15 were measured to investigate the extent of H-bonding interactions of Bet with PG, EG or Gly into DESs in the presence of water by comparing IPA solubility data for each binary (DES + water) system and the corresponding ternary mixtures. The results suggested that the H-bonding interactions between two components of DESs were disappeared when the water content was exceeded 60% (g/g). This result more explored by recording 1H NMR spectra of diluted DESs with deuterium dioxide. Eventually, an endothermic and enthalpy-driven process in most mixtures was determined by thermodynamic analysis of IPA dissolution and mixing processes based on the modified van't Hoff equation.

Extraction of Polyphenols from Slovenian Hop (Humulus lupulus L.) Aurora Variety Using Deep Eutectic Solvents: Choice of the Extraction Method vs. Structure of the Solvent.

Polyphenols from Slovenian hops (Humulus lupulus L.) of the Aurora variety were extracted by different methods and using classical solvents and several deep eutectic solvents (DES) based on choline chloride as the hydrogen bond acceptor component. The obtained extract solutions were analyzed by HPLC for the content of extracted α- and β-acids and extracted xanthohumol. It was found that choline chloride:phenol DES concentrated aqueous solution had an extraction efficiency close to that of diethyl ether, which is considered one of the best classical extraction solvents for polyphenols from hops. The comparison of the extraction efficiency with other choline chloride-based DESs showed that the chemical similarity of the phenol ring in the solvent DES with the polyphenols in hops may be crucial for a highly efficient extraction with choline chloride:phenol DES. On the other hand, the choice of extraction method and the viscosity of the solvents tested seem to play only a minor role in this respect. As far as we know, this is the first study to attempt to relate extraction efficiency in the extraction of hydrophobic solutes to the compressibility of the DES extractants, the latter of which may be correlated with the extent of hydrophobic hydration around the DES components. In addition, using the heating and stirring method for the preparation of choline chloride-based DES concentrated aqueous solutions we found no support for the occurrence of water in two different roles (in the structural and in the dilution role) in these solvents.

Capturing CO2 by ionic liquids and deep eutectic solvents: A comparative study based on multi-level absorbent screening

Because of the high energy consumption and volatility of organic amine solvents in conventional CO2 capture processes, ionic liquids (ILs) and deep eutectic solvents (DESs) have been widely expected as alternative CO2 absorbents. In this work, promising ILs and DESs are identified through a comparative, multi-level absorbent screening method proposed for the first time from a large space of cation–anion combinations and potential DES components, respectively. Important physical properties (namely melting point, viscosity, and toxicity) of potential ILs and salt components of DESs are estimated by a recently-reported deep learning model. Key thermodynamic properties including physically-based absorption and desorption potentials as well as eutectic behaviors between DES component combinations are predicted by the COSMO-RS model. Five EHS (environment, health, and safety) related properties of non-salt components of DESs are assessed by the VEGA platform. From above, the top three ILs and DESs are identified from 5,440 and 38,389 candidates, respectively. The CO2 capture processes based on the retained ILs and DESs are simulated in Aspen Plus in rate-based mode, identifying 1-methyl-1-propylpyrrolidinium bromide: methylimidazole (1:2) as the absorbent with the highest process performance. The experiments shows that the molality-based Henry constant of CO2 in DES is as low as 1.32, validating the competitive absorption performance of this potential DES. Finally, quantum chemistry calculations are conducted to unveil the microscopic absorption mechanism of this DES.

Microextraction of Tigecycline Using Deep Eutectic Solvents and Its Determination in Milk by LC-MS/MS Method.

The occurrence of tigecycline (TGC), a new first glycylcycline antibiotic residues in food products harmfully influences potential human consumers health. Therefore, analysts are forced to develop new microextraction methods connected with modern extractants for effective isolation of this compound. For this purpose, deep eutectic solvents (DES) as the extraction media were used. Liquid-liquid microextraction (LLME) of tigecycline from milk samples with application of the hydrophobic deep eutectic solvents: decanoic acid:thymol (1:1), thymol:camphor (2:1), dodecanoic acid:menthol (2:1), and dodecanoic acid:dodecanol (1:1) was developed. The studied samples were subjected to a deproteinization process using trichloroacetic acid solution and acetonitrile. The optimal microextraction parameters, molar ratio of DES components, amount of extraction solvents, pH of milk sample, shaking, and centrifugation time, were chosen. Tigecycline in the obtained microextracts of deep eutectic solvents was analyzed using a liquid chromatographic technique connected with a tandem mass spectrometry (LC-MS/MS) system. The limits of detection and quantification values for TGC determination followed by DES-LLME-LC-MS/MS method were in the 1.8 × 10-11 mol L-1 (0.01 μg kg-1) to 4.0 × 10-9 mol L-1 (2.28 μg kg-1) and 5.5 × 10-11 mol L-1 (0.03 μg kg-1) to 1.2 × 10-8 mol L-1 (6.84 μg kg-1) ranges, respectively. The RSD values of precision were in the range 1.4-7.8% (intraday) and 5.4-11.7% (interday). The developed procedures were used for the determination of tigecycline in different bovine milk samples.

Unveiling the Influence of Hydrated Deep Eutectic Solvents on the Dynamics of Water-Soluble Proteins.

Deep eutectic solvents (DESs) are mixtures of two or more pure compounds (e.g., Lewis or Brønsted acids and bases, anionic and/or cationic species) in a well-defined stoichiometric proportion, with a melting point lower to that of an ideal liquid mixture. These neoteric solvents are highly tunable through varying the structure or relative ratio of parent components and have been evaluated as solvents able to improve biomolecules' performance, specifically their stability and biocatalytic properties. Inspired by a recent crystallographic study, we have explored through molecular dynamics (MD) simulations the dynamic properties of two different proteins (hen egg-white lysozyme and the human VH antibody fragment HEL4) in a (20% w/w) hydrated solution of choline chloride-glycerol (1:2). We have developed proper force fields to account for DES, protein, and DES-protein interactions, which have been calibrated using pair distribution function measurements of pure DES solutions. MD results show that the presence of DES quenches the protein motion, increasing the rigidity of the overall protein structure. Specific interactions among DES components and protein residues, such as those between choline ions and two Tryptophan residues of lysozyme, may amplify the protein-DES interactions and lead to protein crystallization in the presence of hydrated DES. These findings open new horizons to improve or achieve control on protein properties by a proper choice of hydrated DESs used as solvents.

Role of the Deep Eutectic Solvent Reline in the Synthesis of Gold Nanoparticles.

This work presents a mechanistic understanding of the synthesis of small (<3 nm) gold nanoparticles in a nontoxic, eco-friendly, and biodegradable eutectic mixture of choline chloride and urea (reline) without the addition of external reducing or stabilization agents. Reline acts as a reducing agent by releasing ammonia (via urea hydrolysis), forming gold nanoparticles even at trace ammonia concentration levels. Reline also affects the speciation of the gold precursor forming gold chloro-complexes, stabilizing Au+ species, leading to an easier reduction and avoiding the otherwise fast disproportionation reaction. Such a capability is however lost in the presence of large amounts of water, where water replaces the chloride ligands in the precursor speciation. In addition, reline acts as a weak stabilizing agent, leading to small particles (<3 nm) and narrow distributions although agglomerates quickly form. Such properties are maintained in the presence of water, indicating that it is linked to the urea stabilization rather than the hydrogen-bonding network. This work has important implications in the field of green synthesis of nanoparticles with small sizes, especially for biomedical and health care applications, due to the nontoxic nature of the components of deep eutectic solvents in contrast to the conventional routes.

Deep eutectic solvent as an eco-friendly catalyst for the synthesis of hydroxyphenylglycine methyl ester

The development of deep eutectic solvent (DES) as a green medium and catalyst for sustainable organic synthesis is expanding due to environmental consciousness. DES components are inexpensive, easy to synthesize, non-toxic, biodegradable, and have tunable physicochemical properties. In this study, DESs were formed by a mixture of choline chloride (ChCl) as a hydrogen bond acceptor (HBA), while oxalic acid, glycerol, and urea acted as hydrogen bond donors (HBD). The formed DESs were then characterized by FTIR and their physicochemical properties. DES was applied as a catalyst in the esterification reaction of hydroxyphenylglycine (HPG) to produce hydroxyphenylglycine methyl ester (HPGME), an intermediate material for beta-lactam antibiotics. The result demonstrated that using DES consisting of ChCl-oxalic acid (1:1) could produce HPGME with a yield of 40%. However, further research is essential to investigate the optimum reaction condition, such as the composition of added DES, reaction time, and temperature to obtain a higher yield of HPGME.