Preparation and characterization of nano-CaO based on eggshell waste: Novel and green catalytic approach to highly efficient synthesis of pyrano[4,3-b]pyrans

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. (C) 2014, Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved.