Alkylation of 1-Methylimidazole with 1-Chlorobutane; the ionic liquid 1-Butyl-3-methylimidazolium Chloride
SyntheticPage 747
DOI:
10.1039/SP747
Submitted Jun 18, 2014, published Jul 03, 2014
Matthew Clough (
m.clough11@imperial.ac.uk), Jeraime Griffith (
j.griffith@imperial.ac.uk), Mohamed Rafiq Sulaiman (
m.sulaiman13@imperial.ac.uk), Paul Corbett (
p.corbett13@imperial.ac.uk)
A contribution from
Tom Welton
Chemicals Used
1-Methylimidazole
1-Chlorobutane
Ethyl Acetate
Acetonitrile
Procedure
Primary procedure:
To a two-necked round bottomed flask containing 1-methylimidazole (70 mL, 886.7 mmol) and ethyl acetate (120 mL) was added 1-chlorobutane (120 mL, 1.149 mol) dropwise, with stirring. Once the addition was completed, the reaction mixture was heated to 45 °C for 3 weeks. After being allowed to cool, the upper layer was decanted using a canula. Excess 1-chlorobutane was removed by washing with dry ethyl acetate (3 x 50 mL). Acetonitrile (100 mL) was added to the flask, followed by ethyl acetate (50 mL). Upon adding ethyl acetate, crystallisation occurred. To ensure full crystallisation and no loss of product, the round bottom flask was then cooled to -20 °C overnight. The product was washed with dry ethyl acetate (3 x 50 mL) and subsequently dried under vacuum at 40 °C. The resultant product was obtained as white crystals (82.2%).
A similar but slightly modified procedure is described below:
Freshly distilled 1-chlorobutane (102.85 g, 1.11 mol) was added dropwise (slowly) to a mixture of freshly distilled 1-methylimidazole (82.92 g, 1.01 mol) with ethyl acetate (100 mL), at room temperature. The temperature was increased to 45 °C and the mixture was maintained at this temperature for three days, with vigorous stirring, during which time a biphasic solution had formed. The temperature was further increased to 75 °C and the mixture was maintained at this temperature for four days. The colourless biphasic solution was cooled to room temperature and subsequently placed in a freezer overnight, during which time a white precipitate formed. The solvent was removed by means of Schlenk techniques. The white crystalline solid were washed with ethyl acetate and subsequently were recrystallised from acetonitrile. The residual solution was carefully decanted off, and the white crystalline solid was dried in vacuo to yield 1-butyl-3-methylimidazolium chloride (88.21 g, 50%) as a white crystalline solid.
Author's Comments
Anhydrous conditions are crucial for obtaining moderate to high yields and good purity of the product ionic liquid. For maximum purity, ensure the following:
1. Careful distillation of the starting materials, 1-methylimidazole and 1-chlorobutane, from an appropriate drying agent (KOH for 1-methylimidazole, P2O5 for 1-chlorobutane). Store distilled materials under an inert atmosphere and use canula or syringe apparatus to transfer them into the reaction vessel.
2. Oven and vacuum drying of glassware prior to reaction. Ensure reaction vessel is closed, and glass joints are tight-fitting (avoid grease) to ensure an inert atmosphere.
3. Use pre-dried ethyl acetate and acetonitrile solvents, both for the reaction and recrystallisation stages.
Data
m.p. 69-72 °C.
1H NMR (400 MHz, DMSO-d6): δ 9.37 (s, 1H), 7.84 (t, J = 1.9 Hz, 1H), 7.76 (t, J = 1.7 Hz, 1H), 4.19 (t, J = 7.2 Hz, 2H), 3.87 (s, 3H), 1.77 (p, J = 7.4 Hz, 2H), 1.26 (h, J = 7.4 Hz, 2H), 0.90 (t, J = 7.4 Hz, 3H).
13C {1H} NMR (101 MHz, DMSO-d6): δ 137.14, 128.78, 124.07, 122.74, 48.90, 36.19, 31.84, 19.24, 13.76.
m/z (LSIMS+): 139 (100%) [C4C1im]+.
m/z (LSIMS-): 35 (100%) [35Cl]-, 37 (19%) [37Cl]-.
Calc. for C8H15ClN2: C, 55.01; H, 8.66; N, 16.04%. Found: C, 55.04; H, 8.76; N, 15.89%.
Supplementary Information
Experimental setup for anhydrous alkylation of 1-methylimidazole with 1-chlorobutane.
White crystalline 1-butyl-3-methylimidazolium chloride, [C4C1im]Cl.
C4C1imCl 1H NMR.pdfC4C1imCl 13C NMR.pdfC4C1imCl LSIMS MS +:-.pdf
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Keywords: alkylation, electrophilic, heterocyclic compounds, imidazolium, ionic liquids, nucleophilic, substitution
