Synthesis of coumarins via Pechmann reaction in water catalyzed by acyclic acidic ionic liquids

Some recyclable acyclic SO3H-functionalized ionic liquids have been used as catalysts for Pechmann condensation reaction. N, N, N-trimethyl-N-propanesulfonic acid ammonium hydrogen sulfate [TMPSA][HSO4] has been proved to be the most active catalyst. The coumarins products could simply be separated from the catalyst by filtration and the catalyst could be recycled and reused for several times without noticeably decreasing the catalytic activity.