A Bronsted acidic ionic liquid as an 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 a halogen-free Bronsted acidic ionic liquid, N-methyl-2pyrrolidonium methyl sulfonate ([NMP](+) CH3SO3-). Good conversion rates and high selectivities were obtained, especially for esterification of ethanol by acetic acid, and the liquid esters formed a separate phase that was decanted. The ionic liquid could be reused after removal of water under vacuum.