Calcined Natural Phosphate Doped by Zn as an Efficient Catalyst for the Synthesis of Novel Functional Amidines

Introduction: The present study focuses on the development of doped phosphate cata-lysts for the green synthesis of functional amidines. Methods: The natural phosphate was characterized by XRF, FTIR-IR, and XRD, while the calcined natural phosphate doped with zinc was analyzed using XRD, FTIR-IR, and EDX. Furthermore, the amidines were characterized using 1H and 13C NMR spectroscopy, as well as HRMS analysis. Results: This phosphate catalyst is recyclable and retains its catalytic efficiency over multiple uses. Under optimized conditions, a series of amidines were obtained in high yields up to 95% at room temperature and atmospheric pressure. Discussion: The XRD spectrum of the natural phosphate revealed characteristic peaks of hydroxy-apatite, fluorapatite, and carbonate apatite, along with secondary phases, such as quartz, vermicu-lite, and nacrite. In the zinc-doped material, additional peaks corresponding to zinc oxide and skor-pionite were observed, alongside the original ones. These findings indicate that the primary apatite structure remains intact after doping and calcination, while the appearance of zinc-containing phases suggests that zinc is not incorporated into the apatite lattice, but rather forms separate crys-talline phases. Conclusion: This study presents a straightforward and green process for synthesizing amidines by reacting N-Boc thioacetamide with various amino esters, using calcined natural phosphate doped by zinc as a heterogeneous catalyst.