Alkylation of 1-Methylimidazole with 1-ChlorobutaneAlkylation of 1-Methylimidazole with 1-Chlorobutane
SyntheticPage 747
Published Jul 03, 2014
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.