Ionic Liquid Synthesis In Supercritical CO2 and Gas-Expanded Systems

Ionic liquids have been touted as the next great class of environmentally-friendly solvents due to their lack of vapor-pressure and molecularly “tunable” properties. However, reports of their synthesis often include the very solvents that they will purportedly replace. Moreover, ionic liquids are often too costly as industrial-scale replacements solvents due to little kinetic and thermodynamic data of their synthesis. Novel and benign production methods are highly desirable. This investigation will report kinetics and phase equilibria of the synthesis of a model ionic liquid, 1-hexyl-3-methyl-imidazolium bromide in both CO₂-expanded neat reactions, with CO₂-expanded organic solvents, and in supercritical media. The kinetic constants are extremely sensitive to the solvent environment. Solvatochromic probes and linear solvation energy relationships (LSER) have been used to connect measures of “polarity” with kinetic rate for these reactions. Phase behavior with CO₂ has a large implication on both the reaction and separations scheme and can be used to optimize the entire process.