Sustainable and Scalable Routes to Glycolurils Using Sulphated Zirconia: A Conventional vs. Microwave Approach

Glycolurils are produced industrially in huge quantities for diverse applications, including drilling fluids, paints, fire retardants, and as chemical intermediates. Traditionally, their synthesis involves the condensation of urea and glyoxal in the presence of strong, corrosive acids, which presents significant environmental and handling challenges. To address this, a green and efficient synthetic route using a reusable heterogeneous catalyst, sulphated zirconia (SZ) was developed. This commercially available, cost-effective, and stable catalyst was prepared by a simple solution method and thoroughly characterized. The synthesis of glycoluril was optimized in water, a green solvent, under both conventional and microwave heating conditions. Critical reaction parameters, including catalyst loading, mole ratio, microwave power, temperature, and reaction time, were optimized under both conventional and microwave conditions. Under optimized conventional conditions (80°C, 1 h, 3 mL solvent), a yield of 78% was obtained, whereas microwave-assisted synthesis at 140 W at 4 min (controlled cycle) with 3 mL solvent afforded 72% yield and at 210 W at 1.5 min (continuous method) with 3 mL solvent afforded 65% yield. The catalyst was successfully recovered and reused for multiple cycles with minimal loss of activity. This method presents a moderate, eco-friendly, and industrially scalable process for high-quality glycoluril production.