3.5. Synthesis of Ionic Liquids

Synthesis of 1,3-dimethylimidazolium chloride (1) [35]. In a 250 mL round bottom flask immersed in an ice bath, 10 g of 1-methylimidazole was placed, and 10 mL of HCl (37% aqueous solution) was slowly added. After 20 min, the solvent was evaporated to yield the desired ionic liquid, 1-methylimidazolium chloride, to be used in the following step without further purification. In a Q-tube reactor, 3.0 g of 1-methylimidazolium chloride and 2.28 g of dimethyl carbonate (DMC; 0.025 mmol) were placed, and the mixture was heated at 170 °C for two hours to yield the desired product, 1,3-dimethyl imidazolium chloride 1, in quantitative yield. ¹H-NMR (200 MHz, DMSO-d₆, ppm): δ = 9.46 (s, 1H), 7.87 (s, 2H), 3.87 (m, 6H).

Synthesis of 1,3-dimethylimidazolium dimethylphosphate (2) [19]. In a 250 mL round bottom flask, 21 mL of 1-methyl imidazole (0.263 mol) and 33.4 mL of trimethylphosphate (0.289 mol) were added. The mixture was stirred under heating (100 °C) for 24 h; then, it was washed with Et₂O after cooling to remove residual TMP. The product 1,3-dimethylimidazoium dimethylphosphate was obtained in 95% yield (55.5 g). ¹H-NMR (400 MHz, CDCl₃, ppm): δ = 9.97 (s, 1H), 7.31 (s, 2H), 3.62 (s, 6H), 3.15 (d, 6H, J = 10.5 Hz).

Synthesis of 1-(2-hydroxyethyl)-3-methylimidazolium chloride (3) [36]. In an MW vial, 5 g of 1-methylimidazole (0.061 mol) and 5.39 g of 1-chloroethanol (0.067 mol) were consequently added, and then the reaction was irradiated (200 W) for 15 min at 100 °C. After cooling, the solid product that precipitated off the solution was washed with Et₂O and then dried under vacuum to yield 8.89 g (0.05 mol) of 1-(2-hydroxyethyl)-3-methylimidazolium chloride 3 (90% yield). ¹H-NMR (200 MHz, DMSO-d₆, ppm): δ = 9.33 (s, 1H), 7.79 (m, 2H), 5.50 (bs, OH), 4.23 (t, 2H, 4.8 Hz), 3.86 (s, 3H), 3.67 (t, 2H, J = 4.8 Hz).

Synthesis of 1-(2-hydroxyethyl)-3-methylimidazoliumphosphate (4) [32]. In a MW vial, 0.286 g (1.76 mmol) of 3 and an equimolar amount of TMP (0.3 mL, 1.76 mmol) were placed, and the mixture was irradiated (200 W) for 15 min at 50 °C to yield the desired product 4 in quantitative yield. ¹H-NMR (200 MHz, CDCl₃, ppm): δ = 9.73 (s, 1H), 7.57 (m, 1H), 7.42 (m, 1H), 5.85 (bs, 1H), 4.39 (t, 2H, J = 4.7 Hz), 3.91 (s, 3H), 3.76 (t, 2H, J= 4.7 Hz), 3.53 (d, 6H, J = 11.3 Hz).

Synthesis of 1-butyl-3-methylimidazolium chloride (5) [37]. In a MW vial, 4 mL of 1-methylimidazole (0.0484 mol) and 7.6 mL of 1-chlorobutane (0.0726 mol) were consecutively added; then, the mixture was irradiated (200 W) at 150 °C for 25 min. Then, the supernatant 1-chlorobutane was removed and the mixture was then washed with hexane and diluted with CH₂Cl₂ to be transferred in a round bottom flask for the removal of solvent under vacuum. The desired product 5 was obtained in 90% yield. ¹H-NMR (200 MHz, CDCl₃, ppm): δ = 9.71 (s, 1H), 7.99 (m, 1H), 7.89 (m, 1H), 4.24 (t, 2H, J = 7.0 Hz), 3.91 (s, 3H), 1.77 (m, 2H), 1.30 (m, 2H), 0.88 (t, 3H, J = 7.2 Hz).

Synthesis of 1-butyl-3-methylimidazoliumphosphate (6) [38]. In a 250 mL round bottom flask, 20.25 g (0.11 mol) of 5 and 13.4 mL (0.11 mol) of TMP were consecutively added, and the mixture was heated at 60 °C for 5 h; the product 1-butyl-3-methylimidazolium dimethylphosphate was then obtained in quantitative yield. ¹H-NMR (200 MHz, CDCl₃, ppm): δ = 9.56 (s, 1H), 7.87 (m, 1H), 7.7 (m, 1H), 4.16 (t, 2H, J = 7.1 Hz), 3.83 (s, 3H), 3.30 (d, 6H, J = 10.6 Hz), 1.71 (m, 2H), 1.22 (m, 2H), 0.84 (t, 3H, J = 7.4 Hz).