Tungsten-substituted molybdophosphoric acid impregnated with kaolin: effective catalysts for the synthesis of 3,4-dihydropyrimidin-2(1H)-ones via biginelli reaction

Abstract

A series of highly reusable heterogeneous catalysts (10–25 wt% PMo₇W₅/kaolin), consisting of tungsten-substituted molybdophosphoric acid, H₃PMo₇W₅O₄₀·24H₂O (PMo₇W₅) impregnated with acid treated kaolin clay was synthesized by the wetness impregnation method. The newly synthesized catalyst was fully characterized using inductively coupled plasma-atomic emission spectroscopy (ICP-AES), Fourier transform infrared (FT-IR), powder X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), transmission electron microscopy (TEM), Brunauer–Emmett–Teller (BET) analysis and thermal analysis (TG-DTA). The synthesized materials were shown to be efficient in the synthesis of 3,4-dihydropyrimidin-2(1H)-ones via Biginelli reaction under solvent-free conditions. The obtained results indicate that 20% PMo₇W₅/kaolin catalyst showed remarkably enhanced catalytic activity compared to the bulk PMo₇W₅ catalyst, and also the (10 and 15%) PMo₇W₅ catalyst supported on kaolin clay.