Abstract
Under mild conditions and without any additional organic solvent, esterification of alcohols by carboxylic acids could be carried out in three new halogen-free Brønsted 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.