Ion-Pair Extraction with Tetracyanocyclopentadienides: A Method for Estimating Extraction Efficiency

Abstract

Ion-pair extraction with tetracyanocyclopentadienides (TCCPs) is an effective method for isolating ammonium cations; however, predicting the extractability of ammonium-TCCP ion pairs is challenging. Herein, the measured extraction coefficients (LogK_ex) of ammonium-TCCP ion pairs allowed the values of A (an index for anion extractability) for the TCCP anions to be determined (–3.1 to –1.4); these values were higher than and similar to those of perchlorate and picrate anions, respectively. The correlation between LogK_ex and the sum of the values of A and the calculated Log P of ammonium cations revealed that LogK_ex can be estimated by the equation LogK_ex = A + CLOGP_NR4 + 1.6, where CLOGP_NR4 is the CLOGP value obtained using the “no-plus” ammonium structure. The LogK_ex value can be used to predict the extractability of quaternary ammonium ions.