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The Royal Society of Chemistry"

Synthesis of 1-(2-methoxyethyl)-3-methylimidazolium bis-(trifluoromethanesulfonyl)imide

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Submitted: January 22, 2022, published: February 28, 2022

Authors

Laura Laimina (lauralaimina@gmail.com)

A contribution from 

Reaction Scheme

Chemicals

1-(2-methoxyethyl)imidazole (DOI: 10.1039/D1CP00208B )
Methyl tosylate
Ethyl acetate
Lithium bis(trifluoromethanesulfonyl)imide (Fluorochem, 99%)
Dichloromethane

Procedure

[(C3O)C1im][MeOTs], 1-(2-methoxyethyl)-3-methylimidazolium tosylate. In a 1000 mL two-necked round bottomed flask under argon a solution of 1-(2-methoxyethyl)imidazole (31.25 g, 247.7 mmol, 1 eq) in ethyl acetate (450 mL) was prepared. Methyl tosylate (48.43 g, 260.1 mmol, 1.05 eq) solution in ethyl acetate (40 mL) was added dropwise to the imidazole solution over 30 min with stirring. During the addition, the temperature in the flask was maintained below 30 oC by means of a water bath. The reaction was stirred at room temperature under argon for further 30 min, after which the stirring was stopped and the mixture left at room temperature for 12 h. The solvent and traces of methyl tosylate were removed via canula. The white solid was washed with ethyl acetate (200 mL) following a suction filtration and subsequent ethyl acetate washes on the filter (2x200 mL). The product was dried under high vacuum (0.1 mbar, 48 h) to afford large snow-white crystals (m.p. 104.7 oC, 69.90 g, 91%).

[C3O)C1im][LNTf2], 1-(2-methoxyethyl)-3-methylimidazolium bis-(trifluoromethanesulfonyl)imide. 1-(2-Methoxyethyl)-3-methylimidazolium tosylate (35.37 g, 114.3 mmol, 1 eq) was dissolved in water (50 mL) and  mixed with a solution of lithium bis(trifluoromethanesulfonyl)imide (32.82 g, 114.3 mmol, 1 eq) in water (50 mL).  Dichloromethane (50 mL) was added to the mixture. The organic phase was separated and washed with water (5x20 mL). The dichloromethane solution was filtered through the hydrophobic filter paper and evaporated via rotary evaporation at reduced pressure (60 oC, 1.8 mbar). Stirring under high vacuum (0.1 mbar, 8 h)   afforded a colourless viscous liquid (42.83 g, 92%).

Author Comments

1. All glassware, except mercury thermometer, were pre-heated in the oven at 100 oC for 24 h prior to use. Reagents and solvents were purified via distillation prior to use:
- Ethyl acetate was distilled from CaH2
- 1-(2-Methoxyethyl)imidazole (b.p. 108 oC at 5 Torr)
- Methyl p-toluenesulfonate (methyl tosylate, b.p. 134 oC at 4 Torr)
2. The mercury thermometer was added in a  1000 mL two-necked round bottomed flask to control the reaction temperature. Over the course of reagent addition the reaction mixture warmed up only slightly  (26o - 28 oC).
3. Methyl tosylate was dissolved in ethyl acetate to prevent its crystallization. 
4. After the addition was complete, the stirring was stopped to encourage formation of larger crystals.
5. It was observed the white crystalline imidazolium tosylate salt was not deliquescent unlike most imidazolium ionic liquid intermediate salts.
6. It is advisable to recrystallize the tosylate salt from ethyl acetate prior to the anion exchange.

Data

1H NMR (300 MHz, DMSO-d6, δ): 9.09 – 9.06 (m, 1H), 7.73 – 7.70 (m, 1H), 7.69 – 7.67 (m, 1H), 4.37 – 4.32 (m, 2H), 3.86 (s, 3H), 3.70 – 3.65 (m, 2H), 3.27 (s, 3H) ppm

13C NMR (75 MHz, DMSO-d6, δ): 136.8, 123.5, 122.6, 119.5 (q, 1JCF = 322 Hz), 69.6, 58.1, 48.7, 35.7 ppm

Keywords

alkylation, ether-functionalized ionic liquids, imidazolium, ionic liquids, metathesis, nucleophilic