Selective binding and extraction of aqueous dihydrogen phosphate solutions via three-armed thiourea receptors

A series of neutral anion receptors with one to three thiourea arms were synthesized and their binding to tetrabutylammonium chloride, acetate, and dihydrogen phosphate salts in aqueous DMSO mixtures was examined. The three-armed thiourea host was found to strongly and selectively bind H₂PO₄^- even in DMSO solutions containing up to 30% water. This enabled the dihydrogen phosphate salt to be extracted from water into chloroform in its dibasic form despite the high heat of the hydration of HPO₄^2-.