Melamine Trisulfunic Acid: An Efficient and Recyclable Solid Acid Catalyst for the Synthesis of 4,4′-(Arylmethylene)-bis-(1H-pyrazol-5-ols)

Melamine trisulfunic acid is employed as a recyclable catalyst for the condensation reaction of aromatic aldehydes with 3‐methyl‐l‐phenyl‐2‐pyrazolin‐5‐one. This condensation reaction was performed in ethanol under refluxing conditions giving 4,4′‐(arylmethylene)‐bis‐(3‐methyl‐1‐phenyl‐1H‐pyrazol‐5‐ols) in 80‐96% yields. An efficient synthesis of 4,4′‐(arylmethylene)‐bis‐(3‐methyl‐1‐phenyl‐1H‐pyrazol‐5‐ols) via a tandem condensation reaction of aromatic aldehydes with 3‐methyl‐l‐phenyl‐2‐pyrazolin‐5‐one in the presence of MTSA in refluxing ethanol is described. This catalyst synthetic method has several advantages such as: 1‐ This method seems facile, 2‐ Easy workup, 3‐ Good yields, 4‐ This method gives pure target compounds containing several potential centers for further modification.