1:1.15mol ratio N-methylimidazole and bromobutane were
added into a flask and heated at 70 ◦C for 24 h. After cooling down,
equal volume ethyl acetate was introduced to wash the sample
twice. The sample was evaporated to get the product [Bmim]Br
(1-butyl-3-methylimidazole bromide). [Bmim]Br was metathesis
with PF6
− anion in aqueous solution at 40 ◦C for 24 h. The product
was extracted with CH2Cl2 and washed twice with water. After
evaporation, the product [C4mim]PF6 was obtained.