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

This study presents a simple, efficient, and ecological procedure for the synthesis of biscoumarins and 3,4-dihydropyrano[c]chromenes under green conditions using Zn-3(PO4)(2).4H(2)O as a heterogeneous catalyst. In fact, Zn-3(PO4)(2).4H(2)O 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, Zn-3(PO4)(2.)4H(2)O can be reused at least six times without significant loss of its catalytic activity, because of its long-term durability.