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 ZnCl₂ activation and dual step sulfonation. The resulting catalyst, 2S2Zn-500, exhibited high surface area (739 m²/g), good acidity (0.48 mmol/g SO₃H), 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 ZnCl₂-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.