Choline Chloride Based Deep Eutectic Solvents as a Tuneable Medium for Synthesis of Coumarinyl 1,2,4-Triazoles: Effect of Solvent Type and Temperature

Correlation of solute diffusion with dynamic viscosity in lithium salt-added (choline chloride + glycerol) deep eutectic solvents

Due to their favorable physicochemical properties, deep eutectic solvents (DESs) are finding increased use in chemistry. Metal salt-added DESs are currently being investigated for their potential applications in electrochemistry as a replacement for organic electrolytes. Insights into solute diffusion in salt-added DESs, in this context, are of the utmost importance. Solute diffusion in a LiCl-added DES composed of the H-bond acceptor choline chloride and the H-bond donor glycerol in a 1 : 2 mole ratio, named glyceline, is assessed as a function of temperature and LiCl concentration. For relative translational diffusion, the fluorophore-quencher pair of pyrene-nitromethane is used, whereas for rotational diffusion a fluorescent anisotropic rotor, perylene, is selected. The fluorescence quenching of pyrene by nitromethane was found to be purely dynamic in nature. The estimated bimolecular quenching rate constant (kq) exhibits excellent adherence to the Stokes-Einstein relation, suggesting relative translational diffusion of the solute to be controlled by the dynamic viscosity of the LiCl-added glyceline solution. The rotational reorientation time (θ) of the rotor perylene is also found to scale with dynamic viscosity and obey the Stokes-Einstein relation satisfactorily. Linear correlation between θ and dynamic viscosity (η) improves for glyceline solutions with fixed LiCl concentrations hinting at the possible change in the hydrodynamic volume with LiCl concentration within the DES. Control of rotational diffusion of the solute by the dynamic viscosity is established nonetheless. The effect of earlier reported micro- and/or nano-heterogeneities within salt-added DES systems on solute diffusion dynamics is found to be minimal. The work highlights DESs in offering a solubilizing medium for solutes where the diffusion dynamics are simply controlled by the dynamic viscosity.

Environmentally Friendly Approach to the Synthesis of 3-[Benzylideneamino]-2-methylquinazolin-4(3H)-one Derivatives and Calculation of Their Toxicity

Application of deep eutectic solvents in synthesis of different heterocyclic compounds was proven very efficient. These solvents are a new generation of green solvents showing excellent potential for different purposes, where they are used as environmentally acceptable substitute for toxic and volatile organic solvents. This research describes their application in the synthesis of series of quinazolinone Schiff bases in combination with microwave, ultrasound-assisted and mechanochemical methods. First, a model reaction was performed in 20 different deep eutectic solvents to find the best solvent and then reaction conditions (solvent, temperature and reaction time) were optimized for each method. Afterwards, 40 different quinazolinone derivatives were synthesized in choline chloride/malonic acid (1 : 1) DES by each method and compared by their yields. Here we show that deep eutectic solvents can be very efficient in the synthesis of quinazolinone derivatives as an excellent substitution for volatile organic solvents. With green chemistry approach in mind, we have also performed a calculation on compounds' toxicity and solubility, showing that most of them possess toxic and mutagenic properties with low water solubility.

Choline Chloride-Based Deep Eutectic Solvents as Green Effective Medium for Quaternization Reactions

The Menshutkin reaction represents the alkylation of tertiary amines by alkyl halide where the reactants are neutral and the products, quaternary ammonium salts, are two ions with opposite signs. The most commonly used organic solvents in quaternization reactions are volatile organic solvents (VOSs), namely acetone, anhydrous benzene, dry dichloromethane (DCM), dimethylformamide (DMF) and acetonitrile (ACN). The purpose of this work was to examine eutectic solvents as a "greener" alternative to conventional solvents so that quaternization reactions take place in accordance with the principles of green chemistry. Herein, sixteen eutectic solvents were used as replacements for volatile organic ones in quaternization reactions of isonicotinamide with substituted phenacyl bromides. The reactions were carried out at 80 °C by three synthetic approaches: conventional (4-6 h), microwave (20 min) and ultrasound (3 h). Microwave-assisted organic reactions produced the highest yields, where in several reactions, the yield was almost quantitative. The most suitable eutectic solvents were based on choline chloride (ChCl) as the hydrogen bond acceptor (HBA) and glycerol, oxalic or levulinic acid as hydrogen bond donors (HBDs). The benefits of these three deep eutectic solvents (DESs) as a medium for quaternization reactions are the simplicity of their preparation for large-scale production, with inexpensive, available and nontoxic starting materials, as well as their biodegradability.

Methyl 2-((3-(3-methoxyphenyl)-4-oxo-3,4-dihydroquinazolin-2-yl)thio)acetate

A green synthetic procedure was developed for the two-step synthesis of methyl 2-((3-(3-methoxyphenyl)-4-oxo-3,4-dihydroquinazolin-2-yl)thio)acetate from anthranilic acid, using two green chemistry approaches: utilization of the DES and microwave-induced synthesis. The first step includes a synthesis of 2-mercapto-3-(3-methoxyphenyl)quinazolin-4(3H)-one which was performed in choline chloride:urea DES. In the second step S-alkylation of 2-mercapto-3-(3-methoxyphenyl)quinazolin-4(3H)-one was performed in a microwave-induced reaction. The desired compound was successfully obtained in a yield of 59% and was characterized by different spectral methods.

Application of Deep Eutectic Solvents in the Synthesis of Substituted 2-Mercaptoquinazolin-4(3H)-Ones: A Comparison of Selected Green Chemistry Methods

In this study, deep eutectic solvents (DESs) were used as green and eco-friendly media for the synthesis of substituted 2-mercaptoquinazolin-4(3H)-ones from different anthranilic acids and aliphatic or aromatic isothiocyanates. A model reaction on anthranilic acid and phenyl isothiocyanate was performed in 20 choline chloride-based DESs at 80 °C to find the best solvent. Based on the product yield, choline chloride:urea (1:2) DES was found to be the most effective, while DESs acted both as solvents and catalysts. Desired compounds were prepared with moderate to good yields using stirring, microwave-assisted, and ultrasound-assisted synthesis. Significantly, higher yields were obtained with mixing and ultrasonication (16-76%), while microwave-induced synthesis showed lower effectiveness (13-49%). The specific contribution of this research is the use of DESs in combination with the above-mentioned green techniques for the synthesis of a wide range of derivatives. The structures of the synthesized compounds were confirmed by 1H and 13C NMR spectroscopy.

Some applications of deep eutectic solvents in alkylation of heterocyclic compounds: A review of the past 10 years

This mini-review encapsulates the latest findings (past 10 years) in the field of the deep eutectic solvents (DESs) application in the alkylation/arylation of different heterocyclic compounds. These solvents have been developed to fulfill the green chemistry concept demands and have been proven excellent for the application in various fields. This review describes their application in different types of alkylation, C-, N-, O- and S-alkylation. P-alkylation has not yet been published within this scope. Not only have the authors in this study proven that DESs could be successfully applied for this specific type of reaction, but they have also offered an excellent insight into the mechanisms of their action.