Comparative Study: Ultrasound, Solar, and Mechanochemical Synthesis of 3,4-Dihydropyrimidin-2(1H)-one Catalyzed Al-Pillared Montmorillonite under Solvent Free Conditions

This study reports the green synthesis of 3,4-dihydropyrimidin-2(1H)-one (DHPM) via the Biginelli reaction using aluminum-pillared montmorillonite (Al-Mt), a catalyst derived from Algerian clay. The catalyst was prepared and characterized by X-ray diffraction, Brunauer–Emmett–Teller method X-ray fluorescence spectrometry, and Fourier transform infrared spectroscopy, confirming successful pillaring and enhanced surface area and acidity. Catalytic activity was evaluated under various environmentally friendly conditions, including solvent-free systems, ultrasound irradiation, solar irradiation, and grindstone (mechanochemical) methods. Al-Mt exhibited high efficiency, achieving a 96% yield under solvent-free conditions and 91% yield via grindstone chemistry in just 2.5 h. Solar irradiation also showed promising results with a 64% yield. Compared to raw montmorillonite, the pillared catalyst significantly improved conversion and reaction time. This work highlights Al-Mt as an effective, low-cost, and reusable catalyst for sustainable heterocyclic synthesis, with the grindstone and solar methods representing eco-friendly strategies in DHPM production