HSO3-functionalized Brønsted acidic ionic liquids promote esterification of aromatic acid

Esterification of aromatic acid can be promoted via HSO₃-functionalized Brønsted acidic ionic liquids (ILs). Under the optimum conditions, using 1-(3-sulfonic acid) propyl-3-methylimidazolium hydrogen sulfate (MimC₃SO₃H]HSO₄]) and 1-(4-sulfonic acid) butyl-3-methylimidazolium hydrogen sulfate (MimC₄SO₃H]HSO₄]) as dual solvent-catalysts, the conversion of esterification of aromatic acid was determined to be more than 90%, indicating that HSO₃-functionalized ILs show much better catalytic ability than those of non-functionalized ionic liquids. The separation of desired product was easily performed by extraction with diethyl ether and these HSO₃-functionalized ILs could be reused 7 times after vacuum drying. Our data represent an environmentally friendly method for the preparation of aromatic esters.