One-way extraction of a chemical potential through a liquid membrane: Concept demonstration and applications

A novel concept for the preparation of hydroxide compounds using liquid/liquid anion exchange is presented. The exchange is accomplished by loading a chemical potential into a liquid organic membrane and subsequently releasing it from the membrane using an onium-alcoholate complex as the potential carrier. Accordingly, this method requires no electricity and no energy input other than a concentration gradient. The influence of the alcohol concentration and structure on the extraction equilibrium is studied. Alcohol acidity and stabilization of the alcoholate-quat ion pair are the key factors in determining the transfer efficiency. For example, diols are good coextractants, probably as a result of intramolecular hydrogen bonding that stabilizes the complex. The synthetic application of this concept to make CsOH, LiOH, KOH, and water-soluble tetraalkylonium hydroxides is examined. The extraction mechanism and the function of the organic membrane as a one-way transport medium and a "water pump" are discussed.