Ionic Liquid Synthesis in CO2-Expanded Liquids

A large variety of applications of ionic liquids have been proposed in both the open literature and patents. However, to make these processes both feasible and “green” or sustainable, ionic liquids themselves must be made in large quantities and inexpensively. Moreover, the production of ionic liquids themselves must also be made in an environmentally benign manner. However, reports of their synthesis often include the very solvents that they will purportedly replace, with no kinetic and thermodynamic/separation data. CO₂-expanded liquids (CXLs) have attracted attention due to their tunable properties and relatively lower pressures compared with supercritical processes. The kinetics for the synthesis of ionic liquids is extremely solvent dependent but can be quantitatively correlated using Kamlet-Taft parameters from solvatochromic probes and linear solvation energy relationships (LSER). We report both the kinetics of the reaction at temperatures and pressures with and without organic solvents. The phase behavior of the reactants, products, and CO₂ can be used to tune both the reaction and separation of the ionic liquid product.