Deep Eutectic Solvent-Type Mixture as a Green Catalyst in the Solvent-Free Cycloaddition of CO₂ and Epoxides

A sustainable approach for CO₂ valorization through cycloaddition with epoxides is proposed to synthesize cyclic carbonates, recognized as compounds in green chemistry and industrial applications. A novel deep eutectic solvent (DES)-type catalyst, comprising a mixture of tetrabutylammonium iodide and levulinic acid in a 1:1.5 molar ratio, is introduced and thoroughly characterized. This mixture demonstrates efficiency under mild and solvent-free conditions, providing improved selectivity and conversion rates compared to other related catalysts. This catalyst system (1.4 mol%) operates at atmospheric pressure, avoiding the need for high-pressure equipment while enhancing scalability. Furthermore, this procedure is considered an ideal approach from both economic and ecological perspectives, due to its 100% atom economy and reduced environmental impact, offering a promising, metal-free and low-toxicity alternative. Additionally, the DES-type catalytic system can be recycled for at least three consecutive cycles while maintaining significant activity. Quantum chemistry calculations provide mechanistic insights supporting experimental findings. Overall, these findings underscore the potential of DES-based systems to advance CO₂ utilization technologies, contributing to circular carbon strategies and sustainable chemical synthesis.