“Switchable Water”: Aqueous Solutions of Switchable Ionic Strength

Abstract

"Salting out" is a standard method for separating water-soluble organic compounds from water. In this method, adding a large amount of salt to the aqueous solution forces the organic compound out of the aqueous phase. However, the method can not be considered sustainable because it creates highly salty water. A greener alternative would be a method that allows reversible salting out. Herein, we describe aqueous solutions of switchable ionic strength. Aqueous solutions of a diamine in water have essentially zero ionic strength but are converted by CO(2) into solutions of high ionic strength. The change is reversible. Application to the reversible salting out of THF from water is described.

CO2-responsive polymeric materials: synthesis, self-assembly, and functional applications

“…16). 183 To address this problem, the concept of switchable water (SW), an aqueous solution of switchable ionic strength, was invented by Mercer and Jessop. Because distillation is not required for separating an SHS solvent from a product, there is no need for an SHS to be volatile.…”

Reversible Hydrophobic–Hydrophilic Transition of Ionic Liquids Driven by Carbon Dioxide

“…Jessop et al carried out pioneering work in switching polarity, [1] hydrophility, [2] ionic strength, [3] and viscosity [4] of the solvents by using CO 2 .T hese switchable solvents contain an itrogenous base in the form of amidine,g uanidine,o r amine molecules, [5] and some of them have very little volatility.Itisimportant to find that these switchable solvents have an umber of applications in organic reactions, [3c] extraction, [2c,d, 3a,e] and emulsions. [2a] Recently,I Ls have attracted growing interest as "green" solvents to replace volatile organic solvents in chemical reactions [6] and material synthesis, [7] owing to their extremely low vapor pressure,wide liquid temperature range,n on-flammability,a nd tunable structures and properties.…”

Advances in separation and concentration of microorganisms from food samples

“…Possible approaches for addressing the chemical limitations of current solvent or separation systems, while simultaneously achieving a greener chemical footprint, include the use of next-generation solvents such as ionic liquids (Mester et al , 2010;Han and Armstrong, 2007) and stimulusresponsive materials such as peptide surfactants (pepfactants) (Malcolm et al , 2007) and switchable solvents that can reverse their character (i.e. from hydrophilic to hydrophobic) in response to pH or other external stimuli (Mercer and Jessop, 2010).…”