Design, characterization and application of new ionic liquid 1-sulfopyridinium chloride as an efficient catalyst for tandem Knoevenagel–Michael reaction of 3-methyl-1-phenyl-1H-pyrazol-5(4H)-one with aldehydes

• Catalytic system based on 1-sulfopyridinium chloride was synthesized.
• This catalyst was characterized by IR, 1H as well as 13C NMR, UV and mass spectra.
• This catalytic system was successfully tested in Knoevenagel–Michael reaction.
• The yield of products was obtained 72–93% for 8–16 min under mild conditions.

In this work, novel ionic liquid 1-sulfopyridinium chloride {[Pyridine–SO3H]Cl} is synthesized, and characterized by IR, 1H and 13C NMR, UV as well as mass spectra. The ionic liquid is used as an efficient, homogeneous and reusable catalyst for the synthesis of 4,4′-(arylmethylene)-bis(3-methyl-1-phenyl-1H-pyrazol-5-ol)s by tandem Knoevenagel–Michael reaction of 3-methyl-1-phenyl-1H-pyrazol-5(4H)-one with various aromatic and hetero-aromatic aldehydes under mild reaction conditions.

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