Novel Brønsted acidic ionic liquid as efficient and reusable catalyst system for esterification

Under mild conditions and without any additional organic solvent, esterification of alcohols by carboxylic acids could be carried out in three new halogen-free Bronsted acidic ionic liquids, 1-(4-sulfonic acid) butyl-3-methylimidazolium hydrogen sulfate, 1-(4-sulfonic acid) butylpyridinium hydrogen sulfate and N-(4-sulfonic acid)butyl triethylammonium hydrogen sulfate. Especially for esterification of ethanol by acetic acid, good conversion rate and high selectivity were obtained, and the liquid esters formed a separate phase that was decanted. The ionic liquid could be reused after removal of water under vacuum.