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

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 degrees C than at 700 degrees C. The synthesized nano ZnAl2O4 exhibited a high surface area of 147 m(2) g(-1) with a pore volume of 0.2 cm(3) 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 A(3) 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 N-2 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.