Efficient and green Biginelli reactions in palm oil using a ZnCl2-impregnated sulfonated carbon catalyst derived from corn cob waste

This study presents a novel, sustainable catalytic system for the Biginelli reaction, utilizing a sulfonated carbon catalyst synthesized from underutilized corn cob waste via ZnCl 2 activation and dual step sulfonation. The resulting catalyst, 2S2Zn-500, exhibited high surface area (739 m 2 /g), good acidity (0.48 mmol/g SO 3 H), and well-defined mesoporosity, enabling efficient multicomponent synthesis of dihydropyrimidinones (DHPMs) under mild conditions (95 °C, 5 h) in biodegradable palm oil, a green solvent alternative. This catalyst delivered high yields up to 91% and demonstrated good reusability over five cycles with minimal loss in activity. Comprehensive characterization (XRD, FTIR, SEM–EDS, XPS, Raman, TEM, BET, TGA) confirmed its structural integrity, functional group incorporation, and thermal stability. The system achieved impressive green metrics (Atom Economy: 86–93%; E-factor: 21–32; PMI: 22–33), outperforming several literature-reported biomass-derived catalysts in terms of sustainability, efficiency, and operational simplicity. This is the first report of a ZnCl 2 -activated, sulfonated corn cob catalyst used in tandem with palm oil for Biginelli synthesis, offering a cost-effective, metal-free, and circular approach to biomass valorization. The integration of a renewable feedstock, recyclable catalyst, and eco-friendly solvent positions this work as a compelling model for green multicomponent synthesis and bio-waste utilization.