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Nano-CaO was prepared by calcination of ball-milled chicken eggshell waste.This novel,bioactive,heterogeneous catalyst,which had high catalytic activity and reusability,was used in the green synthesis of pyrano[4,3-b]pyrans via condensation of various aromatic aldehydes,malononitrile,and 4-hydroxy-6-methyl-2H-pyran-2-one at 120 °C under solvent-free conditions.The reaction proceeded to completion within 5–45 min in 93%–98% yield.The nano-CaO was fully characterized by scanning electron microscopy,X-ray powder diffraction,infrared spectroscopy,X-ray fluorescence spectroscopy,and thermal gravimetric,surface area,and elemental analyses.
Nano-CaO was prepared by calcination of ball-milled chicken eggshell waste. This novel, bioactive, heterogeneous catalyst, which had high catalytic activity and reusability, was used in the green synthesis of pyrano [4,3-b] pyrans via condensation of various aromatic aldehydes, malononitrile, and 4-hydroxy-6-methyl-2H-pyran-2-one at 120 ° C under solvent-free conditions.The reaction proceeded to completion within 5-45 min in 93% -98% yield. The nano-CaO was fully characterized by scanning electron microscopy, X-ray powder diffraction, infrared spectroscopy, X-ray fluorescence spectroscopy, and thermal gravimetric, surface area, and elemental analyzes.