Enhanced Anion Exchange For Selective Sulfate Extraction: Overcoming Thernhofmeister Bias

摘要

Synergism in liquid-liquid (L-L) extraction, typified by the combination of a neutral extractant with a cation exchanger to enhance selectively cation extraction strength, has been used and understood for over five decades. Surprisingly, analogous enhancements in anion extraction have yet to be reported. Here, we present a simple way to achieve non-Hofmeister selectivity in L-L anion exchange by combining a synthetic H-bond-donating (HBD) anion receptor with a standard quaternary ammonium type extractant. Specifically, we show that fluorinated calixpyrroles 1 and 2 and the tetraamide macrocycles 3-5 may be used to enhance the solvent extraction of sulfate from nitrate by Aliquat 336-nitrate (CH_3N[(CH_2)_(7-9))CH_3]_3NO_3; A336N).