March 2012
Convenient Syntheses of Bulky Group Containing Imidazolium Ionic Liquids
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2-ArAH); MS (APCI): 153.1(Mþ1). Anal. Calcd. for
C9H17N2I: C, 38.59; H, 6.12; N, 10.00; I, 45.30. Found: C,
38.21; H, 5.83; N, 9.76; I, 45.03.
1,3-Dibenzylimidazolium bromide (12b). Yield 73%; light
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brown semisolid; H NMR(CD3OD, 300 MHz): d 5.46 (s, 4H,
2x CH2), 7.45 (s, 10x ArAH), 7.65 (s, 2H, 2x ArAH), 7.99 (s,
1H, 2-ArAH); MS (APCI): 294.5(Mþ1). Anal. Calcd. for
C17H17N2Br: C, 62.02; H, 5.20; N, 8.51; Br, 24.27. Found: C,
62.40; H, 5.25; N, 8.22; Br, 23.62.
1,3-Dicyclopentylimidazolium bromide (12c). Yield 62%;
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pale semisolid; H NMR(CD3OD, 300 MHz): d 1.80–1.83 (m,
Typical procedure for the synthesis of 1-alkyl-2,3-dime-
thylimidazolium halides 10a–f. To
a solution of 1,2-
dimethylimidazole (2.08 mmol) in CH3CN was added alkyl
halide (6.24 mmol) and reaction was stirred for a time ranging
from 6 minutes to 1 hour at a temperature ranging from 25 to
65ꢁC. The reaction mixture was then washed with diethyl ether
and dried under reduced pressure and purified by column
chromatography.
1,2,3-Trimethylimidazolium iodide (10a). Yield 80%; white
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solid; m.p. 45ꢁC; H NMR(CD3OD, 300 MHz): d 2.60 (s, 3H,
CH3), 3.81 (s, 6H, 2x NACH3), 7.44 (s, 2H, 4,5-ArAH); MS
(APCI): 111.1(Mþ1). Anal. Calcd. for C6H11N2I: C, 30.27; H,
4.66; N, 11.77; I, 53.31. Found: C, 30.44; H, 4.80; N, 11.30; I,
53.62.
1-Ethyl-2,3-dimethylimidazolium iodide (10b). Yield 88%;
white solid; m.p. 92ꢁC; 1H NMR(CD3OD, 300 MHz): d 1.43
(t, 3H, CH3, J ¼ 7.31 Hz), 2.63 (s, 3H, CH3), 3.81 (s, 3H,
NACH3), 4.15–4.23 (m, 2H, NACH2), 7.46 (s, 1H, 5-ArAH),
7.52 (s, 1H 4-ArAH); MS (APCI): 125.1(Mþ1). Anal. Calcd.
for C7H13N2I: C, 33.35; H, 5.20; N, 11.11; I, 50.34. Found: C,
33.51; H, 5.60; N, 11.40; I, 50.14.
16H, 8x CH2), 4.75 (m, 2H, 2x CH), 7.19 (s, 2H, 4-ArAH, 5-
ArAH), 7.98 (s, H, 2-ArAH); MS (APCI): 206.3(Mþ1). Anal.
Calcd. for C13H21N2Br: C, 54.74; H, 7.42; N, 9.82; Br, 28.01.
Found: C, 54.32; H, 7.19; N, 10.07; Br, 27.81.
Typical procedure for synthesis of imidazolium hexa-
fluorophosphate salts 4a–c, 8a–c, 11a–f and 13a–c. To a sol-
utions of the imdazolium halides 3a–c, 7a–c, 10a–f and 12a–c
(1 mmol) in water (2 mL) was added KPF6 (1.3 mmol) and
the reaction mixture was stirred for 1.5 h at room temperature.
Reaction mixture was extracted with dichloromethane (3 ꢂ 5
mL) and purified by column chromatography.
1-Butyl-3-methyl-2-tert-butylimidazolium hexafluorophos-
phate (4a). yield 70%; pale yellow solid; m.p. 84ꢁC; 1H
NMR(CD3OD, 300 MHz): d 0.98 (t, 3H, CH3, J ¼ 7.63 Hz),
1.42 (m, 2H, CH2), 1.65 (s, 9H, 3x CH3), 1.84 (m, 2H, CH2),
4.05 (s, 3H, NACH3), 4.33 (t, 2H, CH2, J ¼ 7.91 Hz), 7.40 (d,
1H, 4-ArA-H, J ¼ 2.02 Hz), 7.50 (d, 1H, 5-ArAH J ¼ 1.99
Hz); MS (APCI): 195.5(Mþ1). Anal. Calcd. for C12H23F6N2P:
C, 42.35; H, 6.81; F, 33.50; N, 8.23; P, 9.10. Found: C, 42.60;
H, 6.57; F, 33.31; N, 8.47; P, 9.33.
1-Butyl-3-methyl-2-isopropylimidazolium hexafluorophos-
phate (4b). Yield 73%; brown liquid; 1H NMR(CD3OD, 300
MHz): d 0.99 (t, 3H, CH3, J ¼ 7.22 Hz), 1.28–1.42 (m, 8H,
2x CH3, CH2), 1.76–1.86 (m, 2H, CH2), 3.61–3.71 (m, H,
CH), 3.91 (s, 3H, NACH3), 4.17–4.22 (t, 2H, CH2, J ¼ 7.43
Hz), 7.42 (s, 1H, 4-ArAH), 7.48 (s, 1H, 5-ArAH); MS
(APCI): 181.1(Mþ1). Anal. Calcd. for C11H21F6N2P: C, 40.49;
H, 6.49; F, 34.94; N, 8.59; P, 9.49. Found: C, 40.60; H, 6.21;
F, 34.78; N, 8.38; P, 9.71.
1-Butyl-3-methyl-2-cyclohexylimidazolium hexafluorophos-
phate (4c). Yield 78%; pale yellow solid; m.p. 123.6 ꢁC; 1H
NMR(CD3OD, 300 MHz): d 0.96 (t, 3H, CH3, J ¼ 7.28 Hz),
1.37 (m, 2H, CH2), 1.71–2.17 (m, 10H, 5x CH2), 3.92 (s, 3H,
NACH3), 4.10 (t, 2H, CH2, J ¼ 7.76 Hz), 7.19 (s, 1H, 5-
ArAH), 7.24 (s, 1H 4-ArAH); MS (APCI): 221.6 (Mþ1). Anal.
Calcd. for C14H25F6N2P: C, 45.95; H, 6.88; F, 31.12; N, 7.65,
P; 8.46. Found: C, 45.66; H, 6.96; F, 30.98; N, 7.34, P; 8.67.
1-Butyl-3-ethylimidazolium hexafluorophosphate (8a). Yield
78%; light brown liquid; 1H NMR(CD3OD, 300 MHz): d
0.98–1.02 (t, 3H, CH3, J ¼ 7.41 Hz), 1.35–1.44 (m, 2H,
CH2), 1.53–1.57 (t, 3H, CH3, J ¼ 7.37), 7.67 (s, 1H, ArAH),
7.68 (s, 1H ArAH), 9.06 (s, 1H ArAH); MS (APCI):
153.4(Mþ1). Anal. Calcd. for C9H17F6N2P: C, 36.25; H,
5.75; F, 38.23; N, 9.39; P, 10.39. Found: C, 35.97; H, 5.61;
F, 38.58; N, 9.59; P, 10.63.
2,3-Dimethyl-1-propylimidazolium iodide (10c). Yield 81%;
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light brown semisolid; H NMR(CD3OD, 300 MHz): d 0.86 (t,
3H, CH3, J ¼ 7.38 Hz), 1.72 (m, 2H, CH2), 2.53 (s, 3H, CH3),
3.72 (s, 3H, NACH3), 3.99 (t, 2H, NACH2, J ¼ 7.35 Hz),
7.36 (s, 1H, 5-ArAH), 7.40 (s, 1H 4-ArAH); MS (APCI):
139.1(Mþ1). Anal. Calcd. for C8H15N2I: C, 36.11; H, 5.68; N,
10.53; I, 47.69. Found: C, 36.52; H, 5.81; N, 10.25; I, 47.91.
1-Isopropyl-2,3-dimethylimidazolium iodide (10d). Yield
77%; light yellow solid; m.p. 136ꢁC; 1H NMR(CD3OD, 300
MHz): d 1.50 (d, 3H, CH3, J ¼ 7.30 Hz), 1.56 (d, 3H, CH3,
J ¼ 6.76 Hz), 2.46 (s, 3H, CH3), 3.69 (s, 3H, NACH3), 4.65–
4.79 (m, 2H, NACH), 7.49 (s, 1H, 5-ArAH), 7.63 (s, 1H 4-
ArAH); MS (APCI): 139.1(Mþ1). Anal. Calcd. for C8H15N2I:
C, 36.11; H, 5.68; N, 10.53; I, 47.69. Found: C, 36.24; H,
5.69; N, 10.33; I, 47.85.
1-Cyclopentyl-2,3-dimethylimidazolium bromide (10e). Yield
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60%; brown semisolid; H NMR(CD3OD, 300 MHz): d 1.78–
1.95 (m, 8H, CH2), 2.63 (s, 3H, CH3), 3.83 (s, 3H, NACH3),
4.73 (m, 1H, NACH), 7.46 (s, 1H, 5-ArAH), 7.52 (s, 1H 4-
ArAH); MS (APCI): 165.1(Mþ1). Anal. Calcd. for
C10H17N2Br: C, 48.99; H, 6.99; N, 11.43; Br, 32.59. Found:
C, 48.65; H, 7.11; N, 11.03; Br, 32.25.
1-Benzyl-2,3-dimethylimidazolium bromide (10f). Yield
96%; brown semisolid; 1H NMR(CD3OD, 300 MHz): d 2.62
(s, 3H, CH3), 3.83 (s, 3H, NACH3), 5.40 (s, 2H, PhACH2),
7.32 (d, 2H, J ¼ 6.03 Hz), 7.38 (m, 3H, J ¼ 6.10), 7.51 (s,
2H 2x ArAH); MS (APCI): 187.1(Mþ1). Anal. Calcd. for
C12H15N2Br: C, 53.95; H, 5.66; N, 10.49; Br, 29.91. Found: C,
54.22; H, 5.29; N, 10.19; Br, 30.19.
Typical procedure for the synthesis of 1,3-dialkylimida-
zolium halides 12a–c. Imidazole (1 mmol) was stirred with
alkyl halide (3 mmol) in presence of potassium carbonate
(3 mmol) in acetone (5 mL) under reflux conditions for 5–8
hours. Reaction mixture was dried under reduced pressure and
column chromatography over silica gel (100:200 mesh) was
performed to afford product.
1,3-Diisopropylimidazolium iodide (12a). Yield 76%; brown
viscous liquid; 1H NMR(CD3OD, 300 MHz): d 1.28 (d, 6H,
2x CH3, J ¼ 6.70 Hz), 1.57 (d, 6H, 2x CH3, J ¼ 6.65 Hz),
4.62–4.83 (m, 1H, CH), 7.74 (s, 2H 2x ArAH), 7.82 (s, 1H,
1-Butyl-3-isopropylimidazolium hexafluorophosphate (8b).
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Yield 80%; light brown liquid; H NMR (CD3OD, 300 MHz):
d 0.94–0.99 (t, 3H, CH3, J ¼ 7.45 Hz), 1.33–1.40 (m, 2H,
CH2), 1.54–1.56 (d, 6H, 2x CH3, J ¼ 6.22 Hz), 1.83–1.89 (m,
2H, CH2), 4.20–4.24 (t, 2H, NACH2), 4.62–4.67 (m, H, CH),
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet