Novel ternary (thio)urea-based eutectic-type mixtures as solvents/catalysts in organic reactions

Ternary choline chloride-based Deep Eutectic Solvents (DESs) generally exhibit enhanced physicochemical properties compared to conventional binary systems, including lower viscosity and melting points, as well as improved thermal stability. These improvements arise from modifications to the hydrogen-bonding network, which reduces intermolecular cohesion and hinders crystallization. In this work, a series of novel ternary liquid mixtures was prepared using choline chloride as the hydrogen bond acceptor and combinations of urea or thiourea derivatives with polyols as hydrogen bond donors. The resulting eutectic systems were comprehensively characterized for viscosity, density, water content, water activity, and pH. These measurements provide insight into the physicochemical behaviour of the ternary mixtures and their suitability as alternative reaction media. Furthermore, the performance of the prepared ternary liquid mixtures was evaluated both as solvents and as catalysts in representative organic transformations. Model reactions included Michael additions and the cyanosilylation/hydrocyanation of different carbonyl compounds. The results highlight the potential of these ternary choline chloride-based eutectic-type mixtures as versatile and tuneable media for sustainable organic synthesis.