Br¨onsted acidic ionic liquids: A green, efficient and reusable catalyst system and reaction medium for Fischer esterification

Abstract

Br¨onsted acidic ionic liquid containing nitrogen-based organic cations 1-methylimidazole and 1-butyl-3-methylimidazolium and inorganic anions of the type BF4−, PF6− and PTSA− has been synthesized in good yields and used as a catalysts and reaction medium for Fischer esterification of alcohols with acids. These were characterized using FTIR and NMR spectroscopy. Ionic liquids as catalyst afforded good alcohol conversion and excellent ester selectivity. Fischer esterification of acetic acid with benzyl alcohol with different Br¨onsted acidic ionic liquids was carried out. Maximum substrate conversion 100% and product selectivity 100% was observed on using [BMIM]+PTSA− as catalyst over a period of 2 h. The ester was easily separated from the reaction mixture and the ionic liquid was reused four times after removing water. No significant loss in catalytic activity was observed on recycling.