Synthesis and characterization of alumina supported molybdosilicic acid (SiMo12/Al2O3): Efficient solid acid catalyst for the synthesis of pyranopyrazole derivatives

A series of highly reusable heterogeneous catalysts (10-40 wt.% SiMo₁₂/Al₂O₃), consisting of molybdosilicic acid (SiMo₁₂) impregnated on alumina (Al₂O₃) support was synthesized by the wetness impregnation method. The physicochemical properties of synthesized catalyst were studied using FT-IR, XRD, SEM, EDX, TEM, BET and TG-DTA analysis techniques. The study proves that the synthesized SiMo₁₂ catalyst efficiently incorporated on the surface of Al₂O_3. The catalytic activity of prepared catalyst was investigated for the synthesis of pyranopyrazole(6-amino-4-phenyl-3-methyl-2,4-dihydropyrano[2,3-c]pyrazole-5carbonitrile) via cyclocondensation reaction of aldehydes, malononitrile, hydrazine hydrate and ethyl-acetoacetate under solvent-free conditions. Among different catalysts, 30% SiMo₁₂ supported on to Al₂O₃ showed the highest catalytic activity. High yield, shorter reaction time, operational simplicity, solvent-free conditions and reusability of the catalyst are the distinct features of this protocol.