Butyl-3-methylimidazolium chloride preparation in supercritical carbon dioxide

A novel process for preparing an ambient-temperature ionic liquid precursor (1-butyl-3-methylimidazolium chloride) was developed. The reaction of 1-methyl imidazole with butyl chloride was conducted in supercritical carbon dioxide (scCO₂) and followed by in situ scCO₂ extraction for purifying the product, l-butyl-3-methylimidazolium chloride. The yield of l-butyl-3-methylimidazolium chloride could be >90%, according to the reaction in a scCO₂ reaction environment. The residual reactants could be, in situ, removed completely using scCO₂ extraction after the required reaction time. The conversion of the reaction is dependent positively and strongly on the pressure. The kinetics of the reaction in scCO₂ could be described using the two-order irreversible reaction model. The reaction rate constant (k) is linearly dependent on the density of CO₂ in the logarithmic coordinates. The ¹H nuclear magnetic resonance ( ¹H NMR) spectral data of the prepared l-butyl-3-methylimidazolium chloride product was satisfactorily consistent with its standard structure. The Fourier transform infrared (FT-IR) spectroscopy results show that the products are as pure as that made via the conventional reaction in the organic solvent/recrystallization method.