Brønsted acidic hydrogensulfate ionic liquid immobilized SBA-15: [MPIm][HSO4]@SBA-15 as an environmentally friendly, metal- and halogen-free recyclable catalyst for Knoevenagel–Michael-cyclization processes

• Ordered mesoporous nanomaterials immobilize ionic liquid.
• Brønsted acidic hydrogensulfate ionic liquid embedded inside the SBA-15.
• A reusable porous catalyst system using commercially available material.
• Represents advantages, operational simplicity, no waste, higher yield and with easy workup.

The Brønsted acidic imidazolium-based metal-free and halogen-free ionic liquid hydrogen sulfate was immobilized on nanoporous silica SBA-15. The structures of synthesized catalysts were investigated using different characterization techniques, including FT-IR, small angle XRD, SEM, TEM and TGA. The [MPIm][HSO4]@SBA-15 is used as an alternative to conventional catalysts in the Knoevenagel–Michael-cyclization processes for the synthesis of tetrahydrochromenes and hexahydroquinoline carboxylates via a multicomponent procedure. The reaction time is reduced drastically and the reaction is progressed in an environmentally friendly way. The immobilized catalyst can be recycled without substantial loss of activity after seven runs.

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