"Switchable Water": Aqueous Solutions of Switchable Ionic Strength

• Published in: ChemSusChem Vol. 3; no. 4; pp. 467 - 470
• Main Authors: Mercer, Sean M., Jessop, Philip G.
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 26-04-2010; WILEY‐VCH Verlag
• Subjects: amines; Bicarbonates - chemistry; carbon dioxide; Carbon Dioxide - chemistry; Carbonic Acid - chemistry; Electric Conductivity; green chemistry; ionic strength; Nitrogen - chemistry; Osmolar Concentration; Polyamines - chemistry; Protons; Salts - chemistry; Solutions; Water - chemistry
• ISSN: 1864-5631; 1864-564X
• DOI: 10.1002/cssc.201000001

“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 CO2 into solutions of high ionic strength. The change is reversible. Application to the reversible salting out of THF from water is described.
“Reversible salting out”: A series of additives dissolved in water can provide a reversible switch in ionic strength when reacted with CO2 providing the first switchable aqueous solvent. This system offers a new recyclable method of salting out water‐miscible organics. Preliminary studies show that up to 87 % of THF can be forced out of a 1:1 (w/w) aqueous solution which can be reversed by removing CO2 from the system.