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

Abstract

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.

Graphical Abstract

An economic, sustainable, and straightforward environmentally friendly synthesis of pyranopyrazole derivatives in presence of catalytic amount of SiMo₁₂/Al₂O₃ under solvent-free condition. Excellent yields, and environmentally sustainability are the main advantages of the present method.

Keywords:

• Alumina
• heteropoly acids
• molybdosilicic acid
• pyranopyrazole

Acknowledgments

The author Shital B. Sukale is gratefully acknowledges the SAARTHI (Chhatrapati Shahu Maharaj Research, Training and Human Development Institute) for junior research fellowship (JRF). We are also thankful to Department of Chemistry, Dr Babasaheb Ambedkar Marathwada University Chhatrapati Sambhajinagar (Aurangabad), India for providing laboratory facility.