Deep eutectic solvent-based emulsification liquid-liquid microextraction for the analysis of phenoxy acid herbicides in paddy field water samples

An emulsification liquid-liquid microextraction (ELLME) method was successfully developed using phenolic-based deep eutectic solvent (DES) as an extraction solvent for the determination of phenoxy acid herbicides, 3,6-dichloro-2-methoxybenzoic acid (dicamba) and 2-methyl-4-chlorophenoxyacetic acid (MCPA) in environmental water samples. Five different phenolics-based DESs were successfully synthesized by using phenol (DES 1), 2-chlorophenol (DES 2), 3-chlorophenol (DES 3), 4-chlorophenol (DES 4) and 3,4-dichlorophenol (DES 6) as the hydrogen-bond donor (HBD) and choline chloride as the hydrogen-bond acceptor (HBA). The DESs were mixed at 1 : 2 ratio. A homogeneous solution (clear solution) was observed upon the completion of successful synthesis. The synthesized DESs were characterized by using Fourier transform infrared and nuclear magnetic resonance (NMR). Under optimum ELLME conditions (50 µl of DES 2 as extraction solvent; 100 µl of THF as emulsifier solvent; pH 2; extraction time 5 min), enrichment factor obtained for dicamba and MCPA were 43.1 and 59.7, respectively. The limit of detection and limit of quantification obtained for dicamba were 1.66 and 5.03 µg l-1, respectively, meanwhile for MCPA were 1.69 and 5.12 µg l-1, respectively. The developed ELLME-DES method was applied on paddy field water samples, with extraction recoveries in the range of 79-91% for dicamba and 82-96% for MCPA.

A Cascade Approach for the Synthesis of 5-(Indol-3-yl)hydantoin: An Application to the Total Synthesis of (±)-Oxoaplysinopsin B

A cascade approach to the synthesis of 5-(indol-3-yl)hydantoin framework has been developed by the reaction of indole with glyoxylic acid/pyruvic acid under a deep eutectic solution, (+)-tartaric acid-dimethylurea. N,N'-Dimethylurea from a deep eutectic solution functions as a reactant as well as a solvent mixture. Isolation of the intermediate, 5-hydroxyhydantoin, and its reaction with indole provides the mechanistic evidence for this reaction. This method was successfully applied in the first total synthesis of an alkaloid, (±)-oxoaplysinopsin B, with an overall yield of 48%.

Copper-catalyzed Goldberg-type C-N coupling in deep eutectic solvents (DESs) and water under aerobic conditions

An efficient and selective N-functionalization of amides is first reported via a CuI-catalyzed Goldberg-type C-N coupling reaction between aryl iodides and primary/secondary amides run either in Deep Eutectic Solvents (DESs) or water as sustainable reaction media, under mild and bench-type reaction conditions (absence of protecting atmosphere). Higher activities were observed in an aqueous medium, though the employment of DESs expanded and improved the scope of the reaction to include also aliphatic amides. Additional valuable features of the reported protocol include: (i) the possibility to scale up the reaction without any erosion of the yield/reaction time; (ii) the recyclability of both the catalyst and the eutectic solvent up to 4 consecutive runs; and (iii) the feasibility of the proposed catalytic system for the synthesis of biologically active molecules.

Hexafluoroisopropanol: the magical solvent for Pd-catalyzed C-H activation

Among numerous solvents available for chemical transformations, 1,1,1,3,3,3-hexafluoro-2-propanol (popularly known as HFIP) has attracted enough attention of the scientific community in recent years. Several unique features of HFIP compared to its non-fluoro analogue isopropanol have helped this solvent to make a difference in various subdomains of organic chemistry. One such area is transition metal-catalyzed C-H bond functionalization reactions. While, on one side, HFIP is emerging as a green and sustainable deep eutectic solvent (DES), on the other side, a major proportion of Pd-catalyzed C-H functionalization is heavily relying on this solvent. In particular, for distal aromatic C-H functionalizations, the exceptional impact of HFIP to elevate the yield and selectivity has made this solvent irreplaceable. Recent research studies have also highlighted the H-bond-donating ability of HFIP to enhance the chiral induction in Pd-catalyzed atroposelective C-H activation. This perspective aims to portray different shades of HFIP as a magical solvent in Pd-catalyzed C-H functionalization reactions.

Ecotoxicity and biodegradability of pure and aqueous mixtures of deep eutectic solvents: glyceline, ethaline, and reline

Most of the works carried out on deep eutectic solvents (DESs) make reference to their physicochemical properties, and the analysis of their toxicological behavior on the environment and biodegradability are still limited. In this work, an exhaustive study on the ecotoxicity of three pure deep eutectic solvents (reline, glyceline, and ethaline) and their mixtures with water (reline-water, glyceline-water, and ethaline-water) was carried out in different biomodels: bacteria (A. fisheri), crustaceans (D. magna), and algae (S. capricornatum). In addition, the amount of chlorophyll in the algae after exposure to the DESs was analyzed. Finally, the biodegradability of the studied DESs was also analyzed. The ecotoxic behavior strongly depends on both the biomodel tested and the presence of water in the mixture, resulting in low toxicities in all cases. Furthermore, most of the deep eutectic solvents studied can be considered readily biodegradable. A comparison of the ecotoxicity and biodegradability of these solvents under other conditions has also been provided, and a complete analysis is given.

Deep Eutectic Solvents as Catalysts for Upgrading Biomass

Deep eutectic solvents (DESs) have emerged as promising green solvents, due to their versatility and properties such as high biodegradability, inexpensiveness, ease of preparation and negligible vapor pressure. Thus, DESs have been used as sustainable media and green catalysts in many chemical processes. On the other hand, lignocellulosic biomass as an abundant source of renewable carbon has received ample interest for the production of biobased chemicals. In this review, the state of the art of the catalytic use of DESs in upgrading the biomass-related substances towards biofuels and value-added chemicals is presented, and the gap in the knowledge is indicated to direct the future research.

Choline Chloride/Glycerol Promoted Synthesis of 3,3-Disubstituted Indol-2-ones

Objective:

3,3-Disubstituted indol-2-one derivatives have wider applications in pharmaceuticals and they are key intermediates for the synthesis of many kinds of drug candidates. The development of an efficient and practical method to prepare this class of compound is highly desirable from both environmental and economical points of views.

Methods:

In order to establish an effective synthetic method for preparing 3,3-disubstituted indol-2-one derivatives, the bis-condensation reaction of isatin and 1H-indene-1,3(2H)-dione was selected as a model reaction. A variety of natural deep eutectic solvent (NADES) were prepared and used for this reaction. The generality and limitation of the established method were also investigated.

Results:

It was found that model reaction can be carried out in natural deep eutectic solvent (NADES) based on choline chloride (ChCl) at 80 oC under microwave irradiation. This protocol with a broad substrate applicability afforded various 2,2'-(2-oxoindoline-3,3-diyl)bis(1H-indene-1,3(2H)-dione) derivatives in high yields.

Conclusion:

simple and efficient procedure has been developed for synthesis of 2,2'-(2-oxoindoline-3,3-diyl)bis(1H-indene-1,3(2H)-dione), spiro[indoline-3,7'-pyrano[5,6-c:5,6-c']dichromene]-2,6',8'-trione, and spiro[indoline-3,9'-xan-thene] trione via bis-condensation between isatin with 1,3-indandione, 4-hydroxycoumarin or 1,3-cyclohexanedione in nat-ural deep eutectic solvent (NADES) based on choline chloride (ChCl) and glycerol (Gl) under microwave irradiation. The salient features of this protocol are avoidance of any additive/catalyst and toxic organic solvent, clean reaction profiles, non-chromatographic purification procedure, and high to excellent yield. Furthermore, the use of NADES as green reaction medium reduces burden on environment and makes the present method environmentally sustainable.

Comprehensive utilization of corncob for furfuryl alcohol production by chemo-enzymatic sequential catalysis in a biphasic system

A new process for the production of furfuryl alcohol from corncob was constructed by using deep eutectic solvents and whole cell catalysis in this paper. Firstly, the corncob was treated with deep eutectic solvents to convert the xylan into furfural, and then the pretreated corncob residue was enzymatically hydrolyzed to obtain a glucose-rich enzymatic hydrolysate, which was used to provide NADH for Bacillus coagulans NL01 during the process of furfural reduction. The furfural yield could reach 46% using the selected choline chloride-oxalic acid as catalysts and corncob as substrate under the optimized catalytic condition at 120 °C for 30 min. The final furfuryl alcohol yield of 20.7% was achieved with corncob as substrate. Moreover, this catalytic system realized the recycling of deep eutectic solvents three times, the high-value production of furfuryl alcohol, and the comprehensive utilization of corncob.

Deep Eutectic Solvent Choline Chloride/p-toluenesulfonic Acid and Water Favor the Enthalpy-Driven Binding of Arylamines to Maleimide in Aza-Michael Addition

Deep eutectic solvents (DESs) have been considered "the organic reaction medium of the century" because they can be used as solvents and active catalysts in chemical reactions. However, experimental and theoretical studies are still needed to provide information on the structures of DESs, the kinetics and thermodynamics properties, the interactions between the DESs and the substrates, the effect of water on the DES supramolecular network and its physicochemical properties, and so forth. This information is very useful to understand the essence of the processes that take place in the catalysis of chemical reactions and, therefore, to help in the design of a DES for a specific reaction and sample. This article shows a systematic study of the impact of DES choline chloride/p-toluenesulfonic acid and DES choline chloride/p-toluenesulfonic acid-water in the aza-Michael addition of arylamines to maleimide to obtain aminopyrrolidine-2,5-dione derivatives. The derivatives are obtained under very mild reaction conditions with good yield. The global reaction is exothermic, spontaneous, permitted by enthalpy, and prohibited for entropy. The calculated potential energy surface shows a reaction mechanism of six steps controlled by enthalpy (except the last step that is controlled by entropy). The water incorporated in the supramolecular DES complex stabilizes the transition states and favors the enthalpy-driven binding. A set of H/D exchange NMR experiments validates the transition state existing in the fourth stage of the mechanism.

Green and efficient synthesis of thioureas, ureas, primary O-thiocarbamates, and carbamates in deep eutectic solvent/catalyst systems using thiourea and urea

An efficient and general catalysis process was developed for the direct preparation of various primary O-thiocarbamates/carbamates as well as monosubstituted thioureas/ureas by using thiourea/urea as biocompatible thiocarbonyl (carbonyl) sources.

Deep eutectic solvents for the preparation and post-synthetic modification of metal- and covalent organic frameworks

The use of deep eutectic solvents (DES) as media for the preparation of metal- and covalent organic frameworks (MOFs and COFs) and their post-synthetic modification towards composites is reviewed.

Optimization of Nazarov Cyclization of 2,4-Dimethyl-1,5-diphenylpenta-1,4-dien-3-one in Deep Eutectic Solvents by a Design of Experiments Approach

The unprecedented Nazarov cyclization of a model divinyl ketone using phosphonium-based Deep Eutectic Solvents as sustainable non-innocent reaction media is described. A two-level full factorial Design of Experiments was conducted for elucidating the effect of the components of the eutectic mixture and optimizing the reaction conditions in terms of temperature, time, and substrate concentration. In the presence of the Deep Eutectic Solvent (DES) triphenylmethylphosphonium bromide/ethylene glycol, it was possible to convert more than 80% of the 2,4-dimethyl-1,5-diphenylpenta-1,4-dien-3-one, with a specific conversion, into the cyclopentenone Nazarov derivative of 62% (16 h, 60 °C). For the reactions conducted in the DES triphenylmethylphosphonium bromide/acetic acid, quantitative conversions were obtained with percentages of the Nazarov product above 95% even at 25 °C. Surface Responding Analysis of the optimized data furnished a useful tool to determine the best operating conditions leading to quantitative conversion of the starting material, with complete suppression of undesired side-reactions, high yields and selectivity. After optimization, it was possible to convert more than 90% of the model substrate into the desired cyclopentenone with cis percentages up to 77%. Experimental validation of the implemented model confirmed the robustness and the suitability of the procedure, leading to possible further extension to this specific combination of experimental designs to other substrates or even to other synthetic processes of industrial interest.

Synthesis of Mannich-type derivatives from amides activated by hydrogen bonding with ZnCl2

The amide group has one of the most significant functionalities found in many natural products. Herein, low-nucleophilic amides are used in a Mannich-type reaction to synthesize N-acyl-protected amine derivatives. A highly efficient synthetic method utilizing simple aldehydes, N-substituted anilines, and amides as substrates was established through a one-pot amide pathway activated by hydrogen bonding between the ZnCl₂ and amide under solvent-free conditions. This strategy can be broadly applied to medicinal chemistry. More importantly, compared with the previous Lewis acid catalyzed reaction, we proposed a new application of zinc chloride.

Solubility Enhancement of Betamethasone, Meloxicam and Piroxicam by Use of Choline-Based Deep Eutectic Solvents

Background: The low aqueous solubility of three important drugs (betamethasone (BETA), meloxicam (MEL) and piroxicam (PIR)) have been increased by use of deep eutectic solvents (DESs) based choline chloride/urea (ChCl/U), choline chloride/ethylene glycol (ChCl/EG) and choline chloride/glycerol (ChCl/G) as new 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. The solubility of drugs in the aqueous DESs solutions was measured at different temperatures with shake flask method. Results: The solubility of the investigated drugs increased with increasing the weight fraction of DESs. The solubility data were correlated by e-NRTL and Wilson models. Also, the thermodynamic functions, Gibbs energy, enthalpy, and entropy of dissolution were calculated. Conclusion: At the same composition of co-solvents and temperature, the BETA, PIR and MEL solubility was highest in (ChCl/U + water), (ChCl/U + water) and (ChCl/EG + water) respectively. The calculated solubility based on these models was in good agreement with the experimental values. In addition, the results show that, the main contribution for drugs solubility in the aqueous DES solutions is the enthalpy.

Ester-mediated peptide formation promoted by deep eutectic solvents: a facile pathway to proto-peptides

The ester-amide exchange reaction enables spontaneous formation of prebiotic proto-peptides under mild conditions. However, this reaction also leads to oligomers with a vast sequence diversity of ester and amide linkages. Here, we demonstrate using deep eutectic solvents as a universal strategy to regulate the reaction pathways and promote the formation of amino acid-enriched oligomers with peptide backbones.

Phytomass Valorization by Deep Eutectic Solvents—Achievements, Perspectives, and Limitations

In recent years, a plethora of extraction processes have been performed by a novel class of green solvents known as deep eutectic solvents (DESs), possessing several environmental, operational, and economic advantages proven by experience when compared to organic solvents and ionic liquids. The present review provides an organized overview of the use of DESs as extraction agents for the recovery of valuable substances and compounds from the original plant biomass, waste from its processing, and waste from the production and consumption of plant-based food. For the sake of simplicity and speed of orientation, the data are, as far as possible, arranged in a table in alphabetical order of the extracted substances. However, in some cases, the isolation of several substances is described in one paper and they are, therefore, listed together. The table further contains a description of the extracted phytomass, DES composition, extraction conditions, and literature sources. With regard to extracted value-added substances, this review addresses their pharmacological, therapeutic, and nutritional aspects. The review also includes an evaluation of the possibilities and limitations of using DESs to obtain value-added substances from phytomass.

Penetration Process of a Hydrated Deep Eutectic Solvent Through the Stratum Corneum and its Application as a Protein Penetration Enhancer

The penetration mechanism of choline chloride-glycerol deep eutectic solvent (DES) through the stratum corneum (SC) as a potential solvent for a novel enhancer of protein penetration into the skin was investigated in a wide and small angle X-ray diffraction study. We found that DES penetrated through intercellular lipids but not the corneocytes. DES seemed to extract a portion of lipids of the short lamellae in the SC. Hydrated DES with a DES to water weight ratio of 9 to 1 (9DES-1H2O) showed the strongest interaction with the lipids in the SC compared with water, DES, and hydrated DESs with another weight ratio of DES to water (DES : water=8 : 2). In a skin penetration test with a fluorescently labelled lysozyme, 9DES-1H2O increased the amount of penetration through the SC by two-fold compared with HEPES buffer.

An Extensive Study of Coumarin Synthesis via Knoevenagel Condensation in Choline Chloride Based Deep Eutectic Solvents

AIM AND OBJECTIVE

In order to preserve the environment from harmful organic solvents, a synthesis of coumarin derivatives was performed in deep eutectic solvents, which are considered as "green" due to their characteristics.

MATERIALS AND METHODS

Choline chloride based deep eutectic solvents (DESs) were employed, both as solvents and as catalysts, in the synthesis of coumarin derivatives via Knoevenagel condensation. In order to find the best DES for coumarin synthesis, 20 DESs were tested for the reaction of salicylaldehyde and dimethyl malonate at 80 °C.

RESULTS

Among the twenty tested deep eutectic solvents only five were adequate for this kind of synthesis. The best DES for this reaction was found to be the one composed of choline chloride:urea (1:2). Most coumarin compounds were obtained in good to excellent yield. Compounds 1g, 2g and 2p should be pointed out due to their yields of 85, 88 and 98 %, respectively. 3-Acetylcoumarins 5a, 5c, 5d, 5e, 5f and 5g were synthesized under ultrasound irradiation and were also obtained in excellent yields of 90, 95, 98, 93, 94 and 85 %, respectively.

CONCLUSION

Series of coumarin derivatives were successfully synthesized, either in choline chloide:urea DES at 80 °C or in ultrasound-assisted reaction, from different salicylaldehydes and active methylene compounds. These "green" methods were found to be very effective in Knoevenagel condensation, while DES was recycled for several cycles without any significant influence on the product yield.

Micellization Behavior of Conventional Cationic Surfactants within Glycerol-Based Deep Eutectic Solvent

The aggregation behavior of two cationic surfactants, i.e., cetyldimethylethanolammonium bromide (CDMEAB) and cetyltributylphosphonium bromide (CTBPB), within an aqueous deep eutectic solvent (DES) is studied. The synthesized DES is composed of 1:2 mole ratio of choline chloride and glycerol and is further characterized by Fourier transform infrared (FTIR) and 1H NMR spectroscopy techniques. The critical micellar concentration (CMC), micellar size, and intermolecular interaction in surfactants within Gly-based DES solutions are investigated by various techniques including surface tension, conductivity, fluorescence, dynamic light scattering (DLS), FTIR, 1H NMR, and two-dimensional (2D) nuclear Overhauser effect spectroscopy (NOESY). The various interfacial properties and thermodynamic parameters are determined in the presence of 5 wt % glyceline (Gly)-based DES in an aqueous solution. The CMC, aggregation number (N agg), and Stern-Volmer constant (K sv) have also been determined by a steady-state fluorescence method. DLS is used to obtain information regarding the size of the aggregates formed by the cationic surfactants in DES solutions. FTIR spectroscopy is used to study the surfactant-DES interactions that tune the micellar structure of the surfactants within the Gly-based DES solution. The functional groups involved in the interactions (H-bonding and electrostatic) are the head groups (HO-CH2-CH2-N+ ion for CDMEAB and quaternary phosphonium (P+) ion for CTBPB) of the surfactants with the -OH-containing Gly DES. The hydrophobic moieties are involved in the hydrophobic interactions. The 1H NMR data show that differences in chemical shifts can provide significant information about the interactions taking place within the system. 1H NMR and NOESY techniques are further employed to strengthen our claim on the feasible structural arrangements within the aqueous surfactant-DES self-assembled structures. It is observed that both the cationic surfactants, i.e., CDMEAB and CTBPB, form self-assembled nanostructures in the Gly-based DES solutions. The present results are expected to be useful for colloidal solutions of DES and their mixtures with water.

Enzymatic Synthesis of Glucose Monodecanoate in a Hydrophobic Deep Eutectic Solvent

Environmentally friendly and biodegradable reaction media are an important part of a sustainable glycolipid production in the transition to green chemistry. Deep eutectic solvents (DESs) are an ecofriendly alternative to organic solvents. So far, only hydrophilic DESs were considered for enzymatic glycolipid synthesis. In this study, a hydrophobic DES consisting of (-)-menthol and decanoic acid is presented for the first time as an alternative to hydrophilic DES. The yields in the newly introduced hydrophobic DES are significantly higher than in hydrophilic DESs. Different reaction parameters were investigated to optimize the synthesis further. Twenty milligrams per milliliter iCalB and 0.5 M glucose resulted in the highest initial reaction velocity for the esterification reaction, while the highest initial reaction velocity was achieved with 1.5 M glucose in the transesterification reaction. The enzyme was proven to be reusable for at least five cycles without significant loss of activity.

Green Asymmetric Organocatalysis

Asymmetric organocatalysis is becoming one of the main tools for the synthesis of chiral compounds that are needed as medicines, crop protection agents, and other bioactive molecules. It can be effectively combined with various green chemistry methodologies. Intensification techniques, such as ball milling, flow, high pressure, or light, bring not only higher yields, faster reactions, and easier product isolation, but also new reactivities. More sustainable reaction media, such as ionic liquids, deep eutectic solvents, green solvent alternatives, and water, also considerably enhance the sustainability profile of many organocatalytic reactions.