Reusable Co3O4/Na-Montmorillonite Composite Catalyst for Efficient Synthesis of 3,4-Dihydropyrimidin-2-(1H)-one Derivatives

A novel catalytic system based on a spinel /Na-montmorillonite composite (Co3O4/Na-Mmt) was developed as an efficient heterogeneous catalyst for the one-pot synthesis of 3,4-dihydropyrimidin-2-(1 H)-ones (DHPMs) using the Biginelli reaction. X-ray diffraction (XRD) confirmed the formation of the Co3O4 spinel phase and its deposition on the montmorillonite, while partial intercalation of cobalt cations within the clay layers was observed. X-ray photoelectron spectroscopy (XPS) verified the oxidation state of cobalt in the composite. Pyridine-FTIR analysis revealed enhanced acidity, predominantly Lewis-type with Bronsted contributions, arising from synergistic interactions between Co3O4 and Na-Mmt. Under solvent-free conditions, the catalyst showed excellent performance, providing high yields (up to 98% obtained with isobutyl acetoacetate) and pure products, as confirmed by ¹H and ¹³C NMR spectroscopy. The composite demonstrated remarkable stability over six consecutive reuse cycles, and hot-filtration tests confirmed its truly heterogeneous nature. These results indicate that Co3O4/Na-Mmt is a sustainable and efficient catalyst for multicomponent reactions such as the Biginelli synthesis. A plausible Lewis acid-assisted mechanism is proposed to explain its superior catalytic performance.