Silica Sulfuric Acid, an Efficient and Recyclable Solid Acid Catalyst for the Synthesis of 4,4′-(Arylmethylene)bis (1H-pyrazol-5-ols)

Abstract

Silica sulfuric acid (SSA) is employed as a recyclable catalyst for the condensation reaction of aromatic aldehydes with 3-methyl-l-phenyl-5-pyrazolone. This condensation reaction is performed in a mixture (1:1 v/v) of water–ethanol at 70 °C, giving 4,4′-alkylmethylene-bis(3-methyl-5-pyrazolones) in 75–93% yields.

Keywords:

• Aldehydes
• 4,4′-(arylmethylene)bis(1H-5-pyrazol-5-ols)
• 5-methyl-2-phenyl-2,4-dihydro-3H-pyrazol-3-one
• silica sulfuric acid
• solid acid

ACKNOWLEDGMENTS

Financial support for this work by the Research Council of Persian Gulf University, Bushehr, Iran, is gratefully acknowledged, and we thank Prof. E. J. Thomas's research group for running the FT-IR and NMR.

Notes

^a Reaction conditions: benzaldehyde (1 mmol), 5-methyl-2-phenyl-2,4-dihydro-3H-pyrazol-3-one (2 mmol), H₂O/EtOH (10 mL) at 70 °C.

^b Isolated yield.

^c The same yield was obtained for a by-product.

^d GC yield of conversion at room temperature.

^a Reaction conditions: benzaldehyde (1 mmol), 5-methyl-2-phenyl-2,4-dihydro-3H-pyrazol-3-one (2 mmol), and catalyst SSA (0.08 g), at 70 °C.

^b Isolated yield.

^a Reaction conditions: aromatic aldehyde (1 mmol) and 5-methyl-2-phenyl-2,4-dihydro-3H-pyrazol-3-one (2 mmol) in a mixture of (1:1 v/v) of H₂O-EtOH (10 ml) and SSA (0.08 g) at 70 °C.

^b Isolated yield.

^c Conversion.

^d Terephthaldehyde (1 mmol), and 5-methyl-2-phenyl-2,4-dihydro-3H-pyrazol-3-one (4 mmol), in a mixture of (1:1 v/v) of H₂O–EtOH (10 ml) and SSA (0.16 g).