Silica chemisorbed bis(hydrogensulphato)benzene (SiO₂-BHSB) as a new, efficient, and recyclable catalyst for the synthesis of 5-oxopyrono[3,2-c]chromene scaffolds in water-based solvent

Abstract

The synthesis of silica chemisorbed bis(hydrogensulphato)benzene (SiO₂-BHSB) as a new hybrid material was achieved by a sequence of three reactions. Structural features of the synthesized SiO₂-BHSB were established by using analytical techniques such as FT-IR, CP-MAS ¹³C NMR, CP-MAS ²⁹Si NMR, EDX, TGA, and DTG. The acid strength of the synthesized material was examined by a simple acid–base volumetric method, which revealed the presence of 3 milliequivalents of acid per gram of the sample. The synthesized material was observed to act as an efficient and recyclable catalyst for the synthesis of 5-oxopyrano[3,2-c]chromene derivatives via a cascade reaction between 4-hydroxycoumarin, malononitrile, and structurally diverse aldehydes in aqueous ethanol under stirring. The sufficiency of a small amount (2.5 mol%) of catalyst, environmentally compatible conditions, operational simplicity, ease of separation, and reusability of the catalyst are the salient features of the presented protocol.

Graphical Abstract

Keywords:

• Bis(hydrogensulphato)benzene
• 4H-hydroxycoumarin
• malononitrile
• recyclable catalyst
• water-based solvent

Acknowledgements

Authors are thankful to the Principal, PVP College, Pravaranagar for providing necessary laboratory facilities. One of the authors, KRK would also like to thank the Director, School of Chemical Sciences, SRTM University, Nanded for their affiliation support.