Hydrophobic, Highly Conductive Ambient-Temperature Molten Salts†

1176 Inorganic Chemistry, Vol. 35, No. 5, 1996 Bonhôteetal.under Ar in 250 mL of absolute ethanol. Then 55.0 g (0.81 mol) ofsodium ethoxide (Fluka, pract.) was added in one portion and theresulting warm solution was stirred for 30 min. Then 88.0 g (0.81mol) of freshly distilled bromoethane (Fluka, purum) was addeddropwise over 1 h. The solution was then refluxed for 30 min. Aftercooling down to room temperature, the mixture was filtered to removethe precipitated NaBr, concentrated on a Rotavapor, refiltered to removesome more NaBr, and finally concentrated at 70 °C, under 100 mbarof pressure. The residual liquid was distilled under 12 mbar of pressureover a 10-cm Vigreux column, collecting the pure 1-ethylimidazole at79-81 °C. Yield: 35.7 g (50%). 1H-NMR (CDCl 3, δ/ppm relativeto TMS): 7.47 (s, 1H), 6.92 (s, 1H), 3.98 (q, 2H, J ) 9.0 Hz), 1.44 (t,3H, J ) 9.0 Hz).1-Ethyl-2-methylimidazole. The same procedure was used, with45.3 g (0.59 mol) of 2-methylimidazole (Fluka, purum) 44.1 g (0.65mol) of sodium ethoxide, and 70.9 g (0.65 mol) of bromoethane in250 mL of absolute ethanol to give a pure fraction of 20 g of productboiling at 94 °C under 11 mbar of pressure (31%). 1H-NMR (CDCl 3,δ/ppm relative to TMS): 6.90 (s, 1H), 6.83 (s, 1H), 3.88 (q, 2H, J )9.0 Hz), 2.38 (s, 3H), 1.37 (t, 3H, J ) 9.0 Hz).1-Ethyl-4-methylimidazole. The same procedure was used, with12.3 g (0.150 mol) of 4-methylimidazole (Fluka, purum), 11.4 g (0.167mol) of sodium ethoxide and 34.9 g (0.224 mol) of iodoethane in 100mL of absolute ethanol to give a pure fraction of 3.2 g of product boilingat 92 °C under 11 mbar of pressure (19%). 1H-NMR (CDCl 3, δ/ppmrelative to TMS): 7.34 (s, 1H), 6.63 (s, 1H), 3.90 (q, 2H, J ) 9.0 Hz),2.12 (s, 3H), 1.41 (t, 3H, J ) 9.0 Hz).1,2-Diethylimidazole. First, 28.83 g (0.30 mol) of 2-ethylimidazole(Fluka, purum) was diluted in 300 mL acetonitrile (Fluka, puriss.). Then21.72 g (0.32 mol) of sodium ethoxide was added, and the solutionwas heated under stirring for 4hto60°C. A solution of 34.88 g(0.32 mol) of bromoethane in 80 mL of acetonitrile was added dropwiseto the vigorously stirred solution, over 2 h. Heating was continuedfor 15 h. The precipitate of NaBr was filtered off and the solvent wasremoved on a Rotavapor. The residue was distilled through a 10 cmVigreux column, under 12 mbar of pressure. The unique fraction wascollected at 93-94 °C: yield 19.30 g (52%). 1H-NMR (CDCl 3, δ/ppmrelative to TMS): 6.94 (d, 1H, J ) 1.5 Hz), 6.83 (d, 1H, J ) 1.5 Hz),3.89 (q, 2H, J ) 9.2 Hz), 2.68 (q, 2H, J ) 9.5 Hz), 1.42-1.30 (2 t,6H, J ) 9.3 Hz).1-Ethyl-3-methylimidazolium bromide (EtMeIm + Br - ). The sameapparatus was used. Under vigorous stirring, 147 g (1.35 mol) offreshly distilled bromoethane was added dropwise over1htoasolutionof 37.0 g (0.45 mol) of 1-methylimidazole (Fluka, puriss.) in 200 mLof 1,1,1-trichloroethane (Fluka, puriss.). The mixture, already turbid,was refluxed for 2 h. The molten salt was decanted from the hotsolution in a separatory funnel, washed twice with 100 mL oftrichloroethane, and dried on a Rotavapor for 1hat70°C under 0.1mbar of pressure: Yield: 78.1 g white solid (91%). In a scaled-upsynthesis, 365.5 g of imidazole and 730 g of bromoethane in 1.5 ltrichloroethane yielded 845 g of MeEtIm + Br - (99.3%). Mp: 76.5 °C.1H-NMR (D 2O, δ/ppm relative to DSS): 8.74 (s, 1H), 7.51 (t, 2H, J )2.2 Hz), 4.25 (q, 2H, J ) 9.3 Hz), 3.91 (s, 3H), 1.52 (t, 3H, J ) 9.3Hz).1-Butyl-3-methylimidazolium Bromide (MeEtIm + Br - ). The sameprocedure was used as for EtMeIm + Br - . From 23.22 g (0.283 mol)of 1-methylimidazole and 39.00 g (0.285 mmol) of bromoethane, therewas obtained 39.4 g of BuMeIm + Br - (64%), as a viscous liquid. 1H-NMR (acetone-d 3, δ/ppm relative to TMS): 10.17 (s, 1H), 8.10 (s,1H), 8.01 (s, 1H), 4.50 (t, 2H, J ) 9.3 Hz), 4.16 (s, 3H), 1.96 (m, 2H),1.37 (m, 2H, J ) 9.5 Hz), 0.95 (t, 3H, J ) 9.1 Hz).1,3-Diethylimidazolium Bromide (Et 2Im + Br - ). The same procedurewas used as for EtMeIm + Br - . From 33.9 g (0.353 mol) of1-ethylimidazole and 96.7 g (0.89 mmol) of bromoethane, there wasobtained 42.5 g of Et 2Im + Br - (59%), mp 53 °C. 1H-NMR (acetoned3, δ/ppm relative to TMS): 10.25 (s, 1H), 7.75 (t, 2H, J ) 2.2 Hz),4.42 (q, 4H, J ) 9.2 Hz), 1.56 (q, 6H, J ) 9.0 Hz).1-Isobutyl-3-methylimidazolium Bromide (i-BuMeIm + Br - ). Thesame procedure was used as for EtMeIm + Br - , except that MeOH wasused as solvent as no reaction took place in trichloroethane. Refluxwas maintained for 15 h. From 17.03 g (0.208 mol) of 1-methylimidazoleand 28.41 g (0.208 mmol) of freshly distilled 1-bromo-2-methylpropane (Fluka, purum), there was obtained 4.33 g of i-BuMeIm + -Br - (9.5%). 1H-NMR (D 2O, δ/ppm relative to DSS): 8.74 (s, 1H),7.47 (m, 2H), 4.04 (d, 2H, J ) 9.0 Hz), 3.92 (s, 3H), 2.16 (sept, 1H,J ) 8.5 Hz), 0.94 (d, 6H, J ) 8.5 Hz).1-Butyl-3-ethylimidazolium Bromide (BuEtIm + Br - ). The sameprocedure was used as for EtMeIm + Br - . From 18.02 g (0.187 mol)of 1-ethylimidazole and 26.08 g (0.190 mmol) of freshly distilledbromobutane (Fluka, purum), there was obtained 39.1 g of BuEtIm + Br -(90%), which becomes glassy upon cooling to -25 °C, withoutcrystallization. 1H-NMR (acetone-d 3, δ/ppm relative to TMS): 10.23(s, 1H), 8.00 (s, 2H), 7.71 (t, 1H, J ) 2.2 Hz), 4.56-4.44 (m, 4H),1.97 (quint, 2H, J ) 9.0 Hz), 1.60 (t, 3H, J ) 9.0 Hz), 0.96 (t, 3H, J) 9.0 Hz).1-Ethyl-2,3-dimethylimidazolium Bromide (EtMe 2Im + Br - ). Thesame procedure was used as for EtMeIm + Br - . From 17.07 g (0.178mol) of 1,2-dimethylimidazole (Aldrich) and 61.7 g (0.566 mmol) ofbromoethane, there was obtained 17.4 g of Et 2Im + Br - (48%) as an oilthat supercools and turns glassy without crystallizing. 1H-NMR (D 2O,δ/ppm relative to DSS): 7.36 (d, 1H, J ) 2.7 Hz), 7.36 (d, 1H, J )2.7 Hz), 4.15 (s, 2H, J ) 9.2 Hz), 3.92 (s, 3H), 3.77 (s, 3H), 2.95 (s,3H), 1.43 (t, 3H, J ) 9.0 Hz).1,3-Dimethylimidazolium Iodide (Me 2Im + I - ). The same procedurewas used as for EtMeIm + Br - , except that the reaction was carried outunder Ar to prevent iodide oxidation. From 32.0 g (0.39 mol) of1-methylimidazole and 55.4 g (0.39 mol) of methyl iodide, there wasobtained 12.0 g Me 2Im + I - (80%), mp 76 °C. 1H-NMR (acetone-d 3,δ/ppm relative to TMS): 9.57 (s, 1H), 7.84 (d, 2H, J ) 2.2 Hz), 4.12(s, 6H).1,3-Dimethylimidazolium Trifluoromethanesulfonate (Me 2-Im + TfO - ). The same procedure was used as for EtMeIm + Br - , exceptthat the reaction was carried out under Ar to prevent methyl triflatehydrolysis, with 1,1,1-trichloroethane stored over molecular sieve([H 2O] ) 1.5 mM). From 4.28 g (52 mmol) o 1-methylimidazole and8.55 g (52 mmol) of methyl triflate (Fluka, purum) diluted in 20 mLof 1,1,1-trichloroethane, there was obtained 12.0 g of Me 2Im + TfO -(94%). 1H-NMR (acetone-d 3, δ/ppm relative to TMS): 9.04 (s, 1H),7.66 (d, 2H, J ) 2.0 Hz), 4.04 (s, 6H).1-Ethyl-3-methylimidazolium Trifluoromethanesulfonate (EtMe-Im + TfO - ). The same procedure was used as for Me 2Im + TfO - . From19.2 g (0.20 mol) of 1-ethylimidazole and 32.1 g (0.196 mol) of methyltriflate, there was obtained 44.9 g of EtMeIm + TfO - (88%). Anal. Calcdfor C 7H 11N 2O 3F 3S: C, 32.31; H, 4.26; N, 10.76; O, 18.44; F, 21.90; S,12.32. Found: C, 31.58/31.60; H, 4.17/4.45; N, 10.34/10.54; O, 19.2/19.3; S, 12.24. 1H-NMR (0.188 M in acetone-d 3, δ/ppm relative toTMS): 9.10 (s, 1H), 7.78 (t, 1H, J ) 2.2 Hz), 7.71 (t, 1H, J ) 2.2Hz), 4.39 (q, 2H, J ) 9.3 Hz), 4.05 (s, 3H), 1.56 (t, 3H, J ) 9.0 Hz).1-Butyl-3-methylimidazolium Trifluoromethanesulfonate (BuMe-Im + TfO - ). The same procedure was used as for Me 2Im + TfO - . From12.42 g (0.100 mol) of redistilled 1-butylimidazole (Aldrich) and 17.23g (0.105 mol) of methyl triflate, there was obtained 26.98 g ofEtMeIm + TfO - (94%). 1H-NMR (acetone-d 3, δ/ppm relative toTMS): 9.11 (s, 1H), 7.77 (t, 1H, J ) 2.2 Hz), 7.71 (t, 1H, J ) 2.2Hz), 4.35 (t, 2H, J ) 9.3 Hz), 4.04 (s, 3H), 2.00-1.90 (m, 2H), 1.38-1.29 (m, 2H), 0.87 (t, 3H, J ) 9.2 Hz).1-(2-Methoxyethyl)-3-methylimidazolium Trifluoromethanesulfonate(MeOEtMeIm + TfO - ). The entire process was carried outunder Ar. In a 250-mL three-necked flask under Ar, 6.10 g (77 mmol)of pyridine (Fluka, puriss., abs.) was added by syringe to a stronglystirred solution of 20.4 g (72 mmol) of trifluoromethanesulfonicanhydride (Aldrich), leading to the formation of an abundant precipitateof N-triflylpyridium triflate. To the cooled mixture (0 °C), was addedby syringe 6.05 g (79.5 mmol) of 2-methoxyethanol (Fluka, puriss.abs). After 15 min at room temperature, the solution was diluted by100 mL of pentane to ensure the complete precipitation of pyridiniumtriflate, filtered quickly, and concentrated to 30 mL on a 30 °C waterbath, under 600 mbar of pressure. To that solution was added dropwiseunder stirring a solution of 5.76 g (70.2 mmol) of 1-methylimidazolein 30 mL of trichloroethane. The mixture was then refluxed for 1 hand worked up as for Me 2Im + TfO - . Yield: 14.11 g (69%). Anal.Calcd for C 8H 13N 2O 4F 3S: C, 33.10; H, 4.51; N, 9.65; O, 22.05; F,19.64; S, 11.05. Found: C, 33.26/33.52; H, 4.58/4.42; N, 10.24/9.97;O, 22.5; S, 10.77. 1H-NMR (acetone-d 3, δ/ppm relative to TMS): 9.05