Application of Phosphate Fertilizer Modified by Zinc as a Reusable Efficient Heterogeneous Catalyst for the Synthesis of Biscoumarins and Dihydropyrano[3,2-c]Chromene-3-Carbonitriles under Green Conditions

Abstract

This study presents a simple, efficient, and ecological procedure for the synthesis of biscoumarins and 3,4-dihydropyrano[c]chromenes under green conditions using Zn3(PO4)2.4H2O as a heterogeneous catalyst. In fact, Zn3(PO4)2.4H2O was prepared for the first time from triple superphosphate fertilizer (TSP) (Ca(H2PO4)2) and zinc sulfate (ZnSO4). Then, it was characterized by spectroscopic and microscopic technics such as X-ray diffraction (XRD), infrared spectroscopy (IR), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDX). The synthesis derivatives of biscoumarins and dihydropyrano[c]chromenes, in the optimal reaction conditions (nature of the solvent, amount of catalyst and temperature), was performed. The obtained results are excellent in terms of time (15–30 min) and yields (81–87%). Besides, Zn3(PO4)2.4H2O can be reused at least six times without significant loss of its catalytic activity, because of its long-term durability.