In this work, novel ionic liquid 1-sulfopyridinium chloride {[Pyridine–SO
H]Cl} is synthesized, and characterized
by IR,
1
H and
13
3
C NMR, UV as well as mass spectra. The ionic liquid is used as an ef?cient,
homogeneous and reusable catalyst for the synthesis of 4,4
-(arylmethylene)-bis(3-methyl-1-phenyl-1Hpyrazol-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.