Ultrasound-assisted solvent-free synthesis of lactic acid esters in novel SO3H-functionalized Brّnsted acidic ionic liquids

Mild and efficient Fischer esterification reactions of lactic acid with a variety of straight chain aliphatic alcohols, cyclohexanol and benzyl alcohol were successfully performed using two novel Brønsted acidic ionic liquids that bear an aromatic sulfonic acid group on the imidazolium or pyridinium cation under ultrasound irradiation. These reactions carried out smoothly with good to excellent conversion rate (78–96%) and satisfactory yields (73–92%) in shorter reaction time (4–6 h) at room temperature when the amount of ionic liquids was 20 mol%. These ionic liquids could be recovered readily and recycled five times without any significant loss in their catalytic activity.