Carbon Dioxide and Molecular Nitrogen as Switches between Ionic and Uncharged Room-Temperature Liquids Comprised of Amidines and Chiral Amino Alcohols

The properties of reversible, room-temperature, chiral, ionic liquids (L-A-C) are reported. They are easily prepared by passing CO2 gas through equimolar mixtures of a simple amidine (L) and a chiral amino alcohol (A), L/A, derived from a naturally occurring amino acid, and they can be returned to their L/A states by passing a displacing gas, N2, through the ionic liquid; the process of passing from uncharged to charged states can be repeated several times without discernible degradation of each phase. All of the 40 L/A combinations examined form room-temperature ionic liquids (most to ca. 50 °C under 1 atm of CO2) and they remain liquids to at least −20 °C. The L-A-C phases are more viscous than their corresponding L/A phases, the conductivities are much higher in the L-A-C phases than in the L/A phases, and the solubility characteristics of the liquids can be modulated significantly by exposing them to either CO2 or N2 gas. The spectroscopic characteristics of the L/A and L-A-C phases have been compared also. Their reversibility, chirality, broad temperature ranges, tolerance to water, and ease of preparation should make the combination of L/A and L-A-C phases useful as solvents for several “green” applications