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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. [ABSTRACT FROM AUTHOR]

Eleven pyridine derivatives were prepared by quaternization reactions by different synthetic routes: conventional, microwave, and ultrasound. Since acetone and other solvents used in conventional quaternization reactions are harmful, attempts were made to replace the organic solvents with more environmentally friendly alternative - deep eutectic solvents. The reactions were carried out using pyridine-3-aldoxime, pyridine-4-aldoxime, isonicotinamide and nicotinamide as nucleophiles and three different dihaloalkanes as electrophiles: diiodopropane, dibromopropane and diiodohexane. The results showed that the microwave method using acetone as solvent was significantly faster and gave higher yields than the conventional method. In contrast, synthesis in the eutectic solvents choline chloride: urea gave significantly lower yields. The structures of the synthesized compounds were confirmed by 1H and 13C NMR spectroscopy, mass spectrometry and elemental analysis. The antifungal activity of all compounds was tested at two different concentrations (10 and 100 µg mL-1) against Botrytis cinerea, Fusarium culmorum, Macrophomina phaseolina and Sclerotinia sclerotiorum in vitro. All tested compounds showed excellent inhibitory activity against the studied phytopathogenic fungal species at a concentration of 100 µg mL-1. [ABSTRACT FROM AUTHOR]