Solvatochromic data have been collected from the literature or newly measured for 83 molecular solvents, 18 switchable solvents, and 187 ionic liquids that have been cited in the green chemistry literature. The data include the normalized Reichardt's parameter (E N T ), the Nile red λ max , and the Kamlet-Taft parameters (α, β, and π*). Disagreements within the literature about the properties of glycerol and poly (ethylene glycol) have been resolved with new data. The switching of a switchable-polarity solvent (also known as a reversible ionic liquid) by CO 2 causes a significant increase in polarity/polarizability (π*) but no change in the basicity (β). A switchable-hydrophilicity solvent undergoes an even greater change in polarity because it merges with an aqueous phase upon exposure to CO 2 . Trends observed from the data of ionic liquids are presented, along with concerns about the best method for determining the Kamlet-Taft parameters.

We report a new class of CO 2 binding organic liquids that chemically capture and release CO 2 much more efficiently than aqueous alkanolamine systems. Mixtures of organic alcohols and amidine/ guanidine bases reversibly bind CO 2 chemically as liquid amidinium/guanidinium alkylcarbonates. The free energy of CO 2 binding in these organic systems is very small and dependent on the choice of base, approximately À9 kJ mol À1 for DBU and Barton's base and +2 kJ mol À1 for 1,1,3,3tetramethylguanidine. These CO 2 capturing agents do not require an added solvent because they are liquid, and therefore have high CO 2 capacities of up to 19% by weight for neat systems, and slightly less when dissolved in acetonitrile. The rate of CO 2 uptake and release by these organic systems is limited by the rate of dissolution of CO 2 into and out of the liquid phase. Gas absorption is selective for CO 2 in both concentrated and dilute gas streams. These organic systems have been shown to bind and release CO 2 for five cycles without losing activity or selectivity.

No abstract

Liquids that consist of a mixture of an alcohol and either an amidine or a guanidine have been developed to switch from a low-polarity form to a high-polarity ionic liquid upon treatment with CO2 at atmospheric pressure. Treatment with N2 and/or mild heat (50−60 °C) reverses the process. These liquids can be used as switchable solvents to dissolve and then precipitate a solute or to dissolve reagents for a chemical synthesis and then precipitate the product.