Ionic liquid [BMIm] [HSO4] as dual catalyst-solvent for the esterification of hexanoic acid with n-butanol

Butyl hexanoate (BuHE) is currently synthesized through the Fischer esterification with mineral acid as catalyst, which suffers from the problems of side reaction, difficult recycling, and corrosion. To overcome these disadvantages, ionic liquid 1-butyl-3-methylimidazolium hydrogen sulfate ([BMIm][HSO4]) is employed as dual catalyst-solvent for the esterification of hexanoic acid (HeAc) with n-butanol (BuOH) in a reactive extraction process. The dual functions of [BMIm][HSO4], extraction and catalysis, were confirmed by liquid-liquid equilibria for the two systems {[BMIm][HSO4] + HeAc + BuHE} and {[BMIm][HSO4] + BuOH + BuHE}, and by the comparison of esterifications with or without [BMIm][HSO4], respectively. Moreover, the optimal reactive extraction conditions for BuHE formation were obtained. Finally, the possible mechanism of intensification of [BMIm][HSO4] on BuHE formation in reactive extraction process was proposed.