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Alkylation of 1-methylimidazole with alkyl chlorides; 1,3-Dialkylimidazolium chlorides

SyntheticPage 792
DOI: 10.1039/SP792
Submitted Jul 29, 2015, published Aug 17, 2015
Jeraime Griffith (j.griffith@imperial.ac.uk)
A contribution from Tom Welton
Reaction Scheme: Alkylation of 1-methylimidazole with alkyl chlorides

Chemicals Used

Anhydrous ethyl acetate
1-Methylimidazole
Activated decolourising charcoal
1-Chloropropane
1-Chloropentane
1-Chloroheptane
1-Chlorooctane
1-Chlorononane
1-Chlorodecane 
Celite®
Deionised water
Anhydrous methanol
0.2 micron PTFE filter
Phosphorous pentoxide
Potassium hydroxide 

Procedure

The haloalkane (1.1eq) was added dropwise to a stirred 1:1 mixture of 1-methylimidazole (1eq) and anhydrous ethyl acetate at 0°C. After complete addition the mixture was stirred at ambient temperature for 30 minutes before slowly warming to 60°C. Progress was monitored by 1HNMR. At 10-14 days the mixture was cooled to ambient temperature and the upper phase of the biphasic mixture was removed under schlenk conditions. Further anhydrous ethyl acetate was added and the mixture stirred vigorously between a few hours to overnight. The upper phase was then removed and the lower (ionic liquid) phase analysed by 1HNMR. The washing step was repeated until the lower  phase was free of starting materials. If necessary, as judged by the colour of the lower phase, activated decolourising charcoal was added and the mixture (in water or methanol) stirred at 50°C overnight then cooled and filtered through a bed of Celite®.  Additional filtration through a 0.2 micron PTFE filter removes any residual particulates. The filtrate was then concentrated under reduced pressure and dried under high vacuum at 55°C to afford clear viscous oils.

Author's Comments

1. Starting materials should be carefully distilled, from an appropriate drying agent (KOH for 1-methylimidazole and P2O5 for 1-chloroalkanes). Store distilled materials under an inert atmosphere and use canula or syringe apparatus to transfer them into the reaction vessel.

2. Oven dry of glassware prior to reaction. Ensure glass joints are tight-fitting (avoid grease) to ensure an inert atmosphere.

3. Higher temperatures (shorter reaction time) leads to a coloured product and tedious purification.

4. 1-Propyl-3-methylimidazolium chloride was obtained as a viscous oil. On prolonged standing it presented as a low melting waxy solid.

5. It is believed that the others remained as (supercooled) ionic liquids in the absence of a seed crystal or nucleation sites.

Data

1-Propyl-3-methylimidazolium chloride - Clear colourless viscous oil (88.8g, 50%); 1HNMR (400 MHz, DMSO-d6) δH 9.40 (1H, s), 7.85 (1H, s), 7.78 (1H, s), 4.16 (2H, t), 3.88 (3H, s), 1.81 (2H, sextet), 0.86 (3H, t). 13CNMR (101 MHz, DMSO-d6) δC 137.28, 124.03, 122.75, 50.57, 36.15, 23.34, 10.86; m/z 125 ([PMIM]+, 100%), 83, 37, 35 (Cl-, 100%), 25.

1-Pentyl-3-methylimidazolium chloride - Clear colourless viscous oil (56g, 47%). 1HNMR (400 MHz, DMSO-d6) δH 9.29 (1H, s), 7.82 (1H, s), 7.74 (1H, s), 4.17 (2H, t), 3.86 (3H, s), 1.79 (2H, quintet), 1.34-1.19 (4H, m), 0.87 (3H, t); 13CNMR (101 MHz, DMSO-d6); m/z 153 ([PentMIM]+, 100%), 55, 43, 41, 37, 35 (Cl-, 100%).

1-Heptyl-3-methylimidazolium chloride - Treated with activated decolourising charcoal. Colourless to pale yellow viscous oil (78.7g, 65%). 1HNMR (400 MHz, DMSO-d6) δH 9.39 (1H, s), 7.85 (1H, s), 7.77 (1H, s), 4.18 (2H, t), 3.88 (3H, s), 1.78 (2H, quintet), 1.32-1.21 (8H, m), 0.86 (3H, t); 13CNMR (101 MHz, DMSO-d6); m/z 181 [HeptMIM]+, 100%), 37, 35 (Cl-, 100%).

1-Octyl-3-methylimidazolium chloride - Pale yellow viscous oil (38.7g, 42%). 1HNMR (400 MHz, DMSO-d6) δH 9.28 (1H, s), 7.82 (1H, s), 7.75 (1H, s), 4.17 (2H, t), 3.87 (3H, s), 1.78 (2H, quintet), 1.32-1.20 (10H, m), 0.86 (3H, t); 13CNMR (101 MHz, DMSO-d6) δC 137.22, 124.02, 122.73, 49.12, 36.15, 31.63, 29.91, 28.96, 28.83, 25.97, 22.52, 14.39; m/z 195 [OctMIM]+, 100%), 83, 37, 35 (Cl-, 100%).

1-Nonyl-3-methylimidazolium chloride - Clear colourless viscous oil (80.1g, 65%). 1HNMR (400 MHz, DMSO-d6) δH 9.38 (1H, s), 7.84 (1H, s), 7.77 (1H, s), 4.18 (2H, t), 3.87 (3H, s), 1.78 (2H, quintet), 1.30-1.21 (12H, m), 0.86 (3H, t); 13CNMR (101 MHz, DMSO-d6) δC 137.22, 124.02, 122.73, 49.12, 36.15, 31.70, 29.91, 29.26, 29.07, 28.88, 25.97, 22.54, 14.40; m/z 209 [NonMIM]+, 100%), 37, 35 (Cl-, 100%).

1-Decyl-3-methylimidazolium chloride - Clear colourless viscous oil (70.1g, 62%). 1HNMR (400 MHz, DMSO-d6) δH 9.31 (1H, s), 7.82 (1H, s), 7.75 (1H, s), 4.17 (2H, t), 3.87 (3H, s), 1.78 (2H, quintet), 1.29-1.21 (14H, m), 0.86 (3H, t); 13CNMR (101 MHz, DMSO-d6) δC 137.20, 124.03, 122.73, 49.14, 36.16, 31.75, 29.91, 29.38, 29.31, 29.14, 28.87, 25.98, 22.55, 14.40; m/z 223 [DecMIM]+, 100%), 83, 43, 41, 37, 35 (Cl-, 100%).
 

Supplementary Information

[C3C1im]Cl, H-NMR, DMSO-d6 (1-Propyl-3-methylimidazolium chloride, H-NMR.pdf)
[C3C1im]Cl, C-NMR, DMSO-d6 (1-Propyl-3-methylimidazolium chloride, C-NMR.pdf)
[C5C1im]Cl, H-NMR, DMSO-d6 (1-Pentyl-3-methylimidazolium chloride, H-NMR.pdf)
[C5C1im]Cl, C-NMR, DMSO-d6 (1-Pentyl-3-methylimidazolium chloride, C-NMR.pdf)
[C7C1im]Cl, H-NMR, DMSO-d6 (1-Heptyl-3-methylimidazolium chloride, H-NMR.pdf)
[C7C1im]Cl, C-NMR, DMSO-d6 (1-Heptyl-3-methylimidazolium chloride, C-NMR.pdf)
[C8C1im]Cl, H-NMR, DMSO-d6 (1-Octyl-3-methylimidazolium chloride, H-NMR.pdf)
[C8C1im]Cl, C-NMR, DMSO-d6 (1-Octyl-3-methylimidazolium chloride, C-NMR.pdf)
[C9C1im]Cl, H-NMR, DMSO-d6 (1-Nonyl-3-methylimidazolium chloride, H-NMR.pdf)
[C9C1im]Cl, C-NMR, DMSO-d6 (1-Nonyl-3-methylimidazolium chloride, C-NMR.pdf)
[C10C1im]Cl, H-NMR, DMSO-d6 (1-Decyl-3-methylimidazolium chloride, H-NMR.pdf)
[C10C1im]Cl, C-NMR, DMSO-d6 (1-Decyl-3-methylimidazolium chloride, C-NMR.pdf)

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Keywords: addition, Alkanes, alkyl/alkenyl/aryl halides, amines, heterocyclic compounds, Ionic liquid, nucleophilic, salts