Facile synthesis of ZnAl2O4 nanoparticles: efficient and reusable porous nano ZnAl2O4 and copper supported on ZnAl2O4 catalysts for one pot green synthesis of propargylamines and imidazo[1,2-a]pyridines by A3 coupling reactions

Abstract

A simple, facile and efficient route was developed for the synthesis of nano ZnAl₂O₄ using ethanolamine. ZnAl₂O₄ nanoparticles were found to be smaller when calcined at 500 °C than at 700 °C. The synthesized nano ZnAl₂O₄ exhibited a high surface area of 147 m² g⁻¹ with a pore volume of 0.2 cm³ g⁻¹. ZnAl₂O₄ nanoparticles were found to be spherical in shape with sizes ranging from 3–7 nm. For the first time, we explored the catalytic activity of nano ZnAl₂O₄ for the synthesis of propargylamines by A³ coupling of aromatic aldehydes, piperidine and phenyl acetylene. High yields were achieved without any side product. We developed Cu/nano ZnAl₂O₄ and utilized it for imidazo[1,2-a]pyridines synthesis by three component coupling of aromatic aldehydes, 2-aminopyridine and phenylacetylene under an N₂ atmosphere. We achieved good yields, and both nano ZnAl₂O₄ and Cu/nano ZnAl₂O₄ were recycled five times successfully. Both the protocols were simple, one pot, solvent-free, economical and involved no additives. They could be an alternative to the existing protocols which involve homogeneous and expensive noble metal catalysts for these reactions.