CO2 as a Separation Switch for Ionic Liquid/Organic Mixtures

• Published in: Journal of the American Chemical Society Vol. 124; no. 35; pp. 10276 - 10277
• Main Authors: Scurto, Aaron M, Aki, Sudhir N. V. K, Brennecke, Joan F
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 04.09.2002
• Subjects: Chemistry; Exact sciences and technology; General and physical chemistry; Solution properties; Solutions; Organic solution; Critical property; Five membered ring; Non aqueous solution; Organic cation; Nitrogen heterocycle; Phase separation; Carbon dioxide; Solubility parameter; Supercritical solvent; Experimental study; Methanol
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja0268682

A novel technique to separate ionic liquids from organic compounds is introduced which uses carbon dioxide to induce the formation of an ionic liquid-rich phase and an organic-rich liquid phase in mixtures of methanol and 3-butyl-1-methyl-imidazolium hexafluorophosphate ([C4mim][PF6]). If the temperature is above the critical temperature of CO2 then the methanol-rich phase can become completely miscible with the CO2-rich phase, and this new phase is completely ionic liquid-free. Since CO2 is nonpolar, it is not equipped to solvate ions. As the CO2 dissolves in the methanol/[C4mim][PF6] mixture, the solvent power of the CO2-expanded liquid is significantly reduced, inducing the formation of the second liquid phase that is rich in ionic liquid. This presents a new way to recover products from ionic liquid mixtures and purify organic phases that have been contaminated with ionic liquid. Moreover, these results have important implications for reactions done in CO2/ionic liquid biphasic mixtures.