Synthesis and characterization of nanostructured Cu-ZnO: An efficient catalyst for the preparation of (E)-3-styrylchromones

Abstract

We have explored nanocrystalline ZnO and Cu-ZnO catalyst for the preparation of 3-styrylchromones with trans selectivity derived from 3-formylchromones. Synthesis of ZnO and Cu-ZnO nano flakes (NFs) was carried by precipitation technique. The analytical techniques such as UV-Visible spectroscopy, X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET), field emission scanning electron microscopy (FESEM) and energy-dispersive analysis X-ray spectroscopy (EDAX) were used to characterize the catalysts. The XRD pattern showed highly pure wurtzite ZnO and Cu-ZnO. The FESEM images showed nano flakes such as sunflower seed morphology in the range width of 9–34 nm and length 90–180 nm. Doping of copper in ZnO was employed to study the selectivity of Knoevenagel and Knoevenagel-Doebner reactions. Knoevenagel condensation was catalyzed efficiently by pure ZnO nano flakes, whereas the Cu-ZnO nano flakes facilitate the Knoevenagel-Doebner reaction. Present synthetic protocols are novel, very clean and high yielding for synthesis of 3-styrylchromones. Almost same yield was observed to the recycled catalyst up to four runs. Keywords: Heterogeneous catalysis, ZnO nano flakes, Knoevenagel condensation, Knoevenagel-Doebner reaction, 3-Styrylchromone