A solvent-free synthesis of coumarins using 1,3-disulfonic acid imidazolium hydrogen sulfate as a reusable and effective ionic liquid catalyst

1,3-Disulfonic acid imidazolium hydrogen sulfate has been used as an effective and reusable ionic liquid catalyst for the synthesis of coumarins from phenol derivatives with beta-ketoesters via the Von Pechmann condensation under solvent-free conditions. This method consistently has the advantages of excellent yields, easy and quick isolation of the products, short reaction times, and green aspects by avoiding toxic catalysts and solvents. Further, the catalyst can be recovered and reused for four times without loss of activity.