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The Royal Society of Chemistry"

Alkylation of 1-Ethylimidazole with Dimethyl Sulfate

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DOI: 

Submitted: October 28, 2013, published: May 27, 2014

Authors

Matthew Clough (m.clough11@imperial.ac.uk)

A contribution from 

Reaction Scheme

Chemicals

1-Ethylimidazole
Dimethyl Sulfate
Toluene 

Procedure

Freshly distilled 1-ethylimidazole (79.6 g, 828 mmol) was diluted with dry toluene (300 ml) in a three-necked round-bottomed flask fitted with a dropping funnel, thermometer and nitrogen line. Freshly distilled dimethyl sulfate (100.7 g, 798 mmol) was added dropwise over seven hours, under a nitrogen atmosphere, taking care to ensure the temperature of the reaction mixture did not exceed 30 oC. During the dropwise addition, a biphasic solution formed. The solution was stirred at room temperature overnight, under a nitrogen atmosphere. The layers were separated, and the lower layer was washed with toluene (3 x 25 ml). The ionic liquid was dried under high vacuum to yield 1-ethyl-3-methylimidazolium methyl sulfate (171.1 g, 96%) as a colourless viscous liquid.

Author Comments

Dimethyl sulfate is HIGHLY TOXIC. Distil dimethyl sulfate at atmospheric pressure. Please use appropriate thick rubber gloves. Quench all glassware / equipment that has come into contact with dimethyl sulfate with concentrated aqueous ammonia. Wipe surfaces with a cloth soaked in the aqueous ammonia. Peform all procedures in a well-ventilated fumehood.

DO NOT cool reaction below room temperature, as this may prevent alkylation occuring; when the mixture warms to room temperature, explosive reaction will occur.

Monitor the temperature of the reaction mixture during the addition of the dimethyl sulfate, maintaining the temperature below 30 oC to avoid discolouration of the ionic liquid. 

Data

Found: 1H NMR (400 MHz, DMSO-d6): δ 9.11 (1H, s), 7.78 (1H, s), 7.69 (1H, s), 4.19 (2H, q, J = 7 Hz), 3.84 (3H, s), 3.37 (3H, s), 1.41 (3H, t, J = 7 Hz). 13C {1H} NMR (100 MHz, DMSO-d6): δ 136.3, 123.6, 122.0, 52.8, 44.1, 35.7, 15.1. ν(neat)/cm-1 3152 3107 (aromatic C-H stretch, m), 2988 2948 2833 (aliphatic C-H stretch, w), 1573 (arom. ring def., m), 1215 (asym. S=O stretch, s) 1003 (sym. S=O stretch, s). m/z (LSIMS+): 111 (100%) [C2C1im]+, 83 (59%) [C1Him]+, 69 (9%) [H2im]+. Calc. for C7H14N2O4S: C, 37.83; H, 6.35; N, 12.60%. Found: C, 37.69; H, 6.38; N, 12.52%.

Lead Reference

M. T. Clough, K. Geyer, P. A. Hunt, J. Mertes and T. Welton, Phys. Chem. Chem. Phys., 2013, 15, 20480.

Keywords

aromatics/arenes, heterocyclic compounds, Imidazolium, Ionic Liquids, substitution, Sulfate