Strongly proton exchanged montmorillonite K10 (H+-Mont) as a solid acid catalyst for highly efficient and environmental benign synthesis of biscoumarins via tandem Knoevenagel-Michael reaction

In this study, synthesis of micro/meso porous acid-activated montmorillonite K10 (H+-Mont) was carried out by the activation of Na+-montmorillonite with HCl (4 M) at the controlled conditions. The prepared H+-Mont clay was then characterized using FT-IR, SEM, EDX, XRD and BET analyses. SEM and BET surface analyses represented that by the acid-activation, adjacent layers of montmorillonite K10 (Mont K10) were exfoliated to tiny segments leading to raise of surface area and total pore volume in H+-Mont system rather than the alone Mont K10. Catalytic activity of the prepared H+-Mont clay was further studied as a potent solid acid catalyst for synthesis of biscoumarin materials via tandem Knoevenagel-Michael reaction of 4-hydroxycoumarin with aromatic aldehydes. All reactions were carried out in a mixture of H2O-EtOH (1:1) at room temperature to afford the products in high to excellent yields within 25-50 min. (C) 2019 Elsevier Ltd. All rights reserved.