Sulfonic acidic ionic liquids: Efficient and environmentally benign catalysts for esterification

Esterification of salicylic acid with alcohols was investigated in the presence of Sulfonic Acidic Ionic Liquids (ILs). The catalytic activity of each ILs was dependent on both cation and anion. Two acidic ILs 1-methyl-3(3- sulfopropyl)-imidazolium hydrogensulfate ([MIMPS] [HSO₄]) and N-propanesulfonic acid pyridinium hydrogensulfate ([PSPy][HSO₄]) showed good activity. Esterification with primary alcohols gave the higher yield compared with secondary alcohols. Especially, ILs could be separated easily from the product and be reused eight times without significant loss of activity. Therefore, an efficient and environmentally benign approach for esterification of salicylic acid was provided.