Bronsted Acidic Ionic Liquid as an Efficient and Reusable Catalyst for Synthesis of Pyrazoles and β-Enaminones

A simple, efficient and ecofriendly protocol for the synthesis of pyrazoles and β-enaminones using halogen free Bronsted acidic ionic liquid N-methyl-2-pyrrolidone hydrogen sulfate as a reusable catalyst has been developed. The prepared ionic liquids were characterized by different techniques like NMR and their Bronsted acidity was measured using infrared spectroscopy using pyridine as a probe molecule and monitoring the band in the range of 1350-1600 cm-1 arising from its ring vibration modes. Present catalytic system is simple, works at ambient conditions and requires shorter reaction time to furnish excellent yield of the desired products under solvent free conditions for majority of substrates. The ionic liquid shows very good catalytic activity and reusability up-to six recycles and gave good to excellent yields of the desired products.