PAPER
Expedient Synthesis of Symmetric Aryl Ketones and of Ambient-Temperature Molten Salts of Imidazole
1257
HCl (1 N, 50 mL) at 0 °C. The reaction vessel was allowed to warm
to r.t., the layers were separated, and the aqueous layer was extract-
ed with Et2O (3 ¥ 50 mL). The combined organic layers were dried
(MgSO4), the solvent was evaporated and the residue was dried un-
der vacuum to yield 4.64 g of a dark colored mass (78%). The prod-
uct thus obtained was then used without further purification. An
analytical sample was obtained by chromatography (dissolved in
CCl4 and eluted with petroleum ether/Et2O, 3:1) and recrystallized
from Et2O/petroleum ether.
13C NMR (CDCl3): d = 13.07, 19.05, 31.78, 36.33, 49.41, 121.94,
123.49, 136.74.
1-Butyl-3-methylimidazolium Bis((trifluoromethyl)sulfonyl)-
amide (BuMeIm+Tf2N-)
A solution of lithium bis((trifluoromethyl)sulfonyl)amide (LiTf2N,
20.27 g, 70.63 mmol) in deionised H2O (60 mL) was added to a so-
lution of 1-butyl-3-methylimidazolium bromide (15.48 g, 70.63
mmol) in deionised H2O (20 mL). The mixture was heated for over
2 h at 70 °C. The solution was extracted with CH2Cl2 and the extract
was washed with deionised H2O and then dried under reduced pres-
sure to afford 27.62 g (93%) of BuMeIm+Tf2N- as a colorless liq-
uid.
1H NMR (CDCl3): d = 0.96 (t, 3H, J = 7.4 Hz), 1.36 (m, 2H), 1.85
(m, 2H), 3.94 (s, 3H), 4.17 (t, 2H, J = 7.4 Hz), 7.31 (m, 2H), 8.76
(s, 1H).
Mp: 73 °C (Lit.27 72-73 °C).
IR (KBr): n = 3113, 1700, 1695, 1629, 1511, 1426, 1266, 1136, 847,
826, 740, 696 cm-1.
1H NMR: d = 7.38 (dd, J = 5.1, 3.0 Hz, 2H, H-5+5'), 7.60 (dd,
J = 5.1, 1.3 Hz, 2H, H-4+4'), 8.01 (dd, J = 3.0, 1.3 Hz, 2H, H-2+2').
These spectroscopic data were similar to those reported in the liter-
ature.29
13C NMR (CDCl3): d = 126.30 (2 CH), 128.23 (2 CH), 132.64 (2
CH), 142.02 (2C), 183.24 (C).
13C NMR (CDCl3): d = 13.15, 19.31, 31.89, 36.30, 49.95, 120.00 (q,
2C, JC-F = 322 Hz), 122.23, 123.66, 136.08.
Anal. Calcd for C10H15F6N3O4S2: C, 28.64; H, 3.61; N, 10.02; S,
15.29. Found: C, 28.67; H, 3.63; N, 9.98; S, 15.19.
GC-MS (70 eV): m/z (%) = 194 (M+, 61), 111 (M+-Th, 100), 83
(Th+, 15).
1-Ethyl-3-methylimidazolium Bromide (EtMeIm+Br-)
Anal. Calcd for C9H6OS2: C, 55.64; H, 3.11; S, 33.01. Found: C,
55.48; H, 3.08; S, 33.01.
Same procedure as for BuMeIm+Br-: From 1-methylimidazole
(5.8 g, 70.63 mmol) and bromoethane (23.1 g, 211.9 mmol), Et-
MeIm+Br- was obtained as a white solid, yield: 13.49 g (95%).
2,2-Di(3-thienyl)-1,3-dioxolane 3
1H NMR (CDCl3): d = 1.34 (t, 3H, J = 7.4 Hz), 3.87 (s, 3H), 4.18 (q,
2H, J = 7.4 Hz), 7.48 (d, 2H, J = 1.7 Hz), 9.98 (s, 1H).
13C NMR (CDCl3): d = 15.05, 35.96, 44.51, 121.50, 123.13, 135.95.
To a cooled stirred CH2Cl2 solution (25 mL) containing the crude
ketone 2 (5.83 g, 30 mmol), were successively added 1,2-bis(trime-
thylsilyloxy)ethane (12.8 g, 62 mmol) and trimethylsilyl trifluo-
romethanesulfonate (0.56 mL, 3 mmol, 10% mol) at 0 °C. The
mixture was stirred at r.t. for an additional 3 h, quenched by the ad-
dition of dry pyridine (1 mL), poured into sat. NaHCO3 (25 mL) and
extracted with Et2O (3 ¥ 25 mL). The combined extracts were dried
(1:1 mixture of Na2CO3 and Na2SO4) and evaporated. The crude
product was purified by chromatography (petroleum ether/CH2Cl2,
1:1). The product was thus crystallized from light petroleum as col-
orless plates (4.72g, 66%), mp: 111 °C (Lit.28 113-114 °C).
1-Ethyl-3-methylimidazolium Bis((trifluoromethyl)sulfonyl)
amide (EtMeIm+Tf2N-)
Same procedure as for BuMeIm+Tf2N-: From 1-Ethyl-3-methylim-
idazolium bromide (13.49 g, 70.63 mmol) and LiTf2N (20.28 g,
70.63 mmol), EtMeIm+Tf2N- was obtained as a colorless liquid,
yield: 23.64 g (90%).
1H NMR (DMSO-d6): d = 1.41 (t, 3H, J = 7.4 Hz), 3.84 (s, 3H), 4.19
(q, 2H, J = 7.4 Hz), 7.66 (t, 1H, J = 1.7 Hz), 7.75 (t, 1H, J = 1.7 Hz),
9.1 (s, 1H).
13C NMR (DMSO-d6): d = 15.17, 35.85, 44.38, 120.00 (q, 2C,
JC-F = 322 Hz), 122.16, 123.77, 136.47.
IR (KBr): 3097, 2968, 2876, 1609, 1411, 1264, 1071, 809 and 736
cm-1.
1H NMR (CDCl3): d = 4.09 (s, 4H, H-4+5), 7.09 (dd, J = 5.0, 1.3
Hz, 2H, H-4'+4''), 7.26 (dd, J = 5.0, 3.1 Hz, 2H, H-5'+5'') and 7.30
(dd, J = 3.1, 1.3 Hz, 2H, H-2'+2'').
Anal. Calcd for C8H11F6N3O4S2: C, 24.56; H, 2.83; N, 10.74; S,
16.39. Found: C, 24.37; H, 3.05; N, 10.72; S, 16.24.
These spectroscopic data were similar to those reported in the liter-
ature.28
13C NMR (CDCl3): d65.06 (2 CH2), 106.06 (C), 123.03 (2 CH),
1-Ethyl-2-methyl-3-methylimidazolium Bromide (EtMe-
MeIm+Br-)
125.94 (2 CH), 126.32 (2 CH) and 143.59 (2C).
Same procedure as for BuMeIm+Br-: From 1-methy-2-methyl
imidazole (6.0 g, 62.42 mmol) and bromoethane (20.4 g,
187.24 mmol), EtMeMeIm+Br- was obtained as a white solid, yield:
11.40 g (89%).
GC-MS (70 eV): m/z (%) = 238 (M+, 9), 166 (20), 155 (100), 111
(73), 83 (13).
Anal. Calcd for C11H10O2S2: C, 55.44; H, 4.23; S, 26.90. Found: C,
55.18; H, 4.16; S, 26.79.
1H NMR (CDCl3): d = 1.47 (t, 3H, J = 7.4 Hz), 2.80 (s, 3H), 3.98 (s,
3H), 4.28 (q, 2H, J = 7.4 Hz), 7.61 (d, 1H, J = 1.9 Hz), 7.69 (d, 1H,
J = 1.9 Hz).
13C NMR (CDCl3): d = 10.83, 15.19, 36.01, 44.02, 120.64, 122.97,
143.46.
1-Butyl-3-methylimidazolium Bromide (BuMeIm+Br-)
Bromobutane (9.76 g, 71.23 mmol) was added dropwise with
vigorous stirring to a solution of 1-methylimidazole (5.8 g,
70.63 mmol) in toluene (30 mL), and the mixture was refluxed for
3 h. The melt was decanted from the hot solution and the toluene
phase was removed via canula. The ionic liquid was washed 4 times
with EtOAc and dried under reduced pressure.
1-Ethyl-2-methyl-3-methylimidazolium Bis((trifluoromethyl)-
sulfonyl) amide (EtMeMeIm+Tf2N-)
Same procedure as for BuMeIm+Tf2N-: From 1-Ethyl-2-methyl-3-
methylimidazolium bromide (10.0 g, 48.75 mmol) and LiTf2N
(14.00 g, 48.75 mmol), EtMeMeIm+Tf2N- was obtained as a color-
less liquid, yield: 19.76 g (89%).
Viscous colorless liquid, yield: 15.48 g (100%).
1H NMR (CDCl3): d = 0.94 (t, 3H, J = 7.4 Hz), 1.38 (m, 2H), 1.91
(m, 2H), 4.12 (s, 3H), 4.35 (t, 2H, J = 7.4 Hz), 7.61 (t, 1H, J = 1.8
Hz), 7.74 (t, 1H, J = 1.8 Hz), 10.26 (s, 1H).
Synthesis 2000, No. 9, 1253–1258 ISSN 0039-7881 © Thieme Stuttgart · New York