Efficient Ion-Pair Extraction of Potassium Chloride from Aqueous Phase into Nitrobenzene Containing Dicyclohexyl-18-crown-6 as Cation Binder and Diphenylthiourea as Anion Binder

Abstract

Ion-pair recognition of cationic and anionic guest species by bifunctional receptors is a current topic in molecular recognition chemistry. [1][2][3][4][5] Recently Beer et al. have designed novel rhenium(I) bipyridyl amide crown ether receptors and shown that these receptors complexed to form K + Cl -ion pairs in which complexation of crown ether moiety with K + cooperated in the binding of Cl -in organic solution. 6 Reinhoudt et al. have also shown that calix[4]arenes bearing urea moieties behave as bifunctional receptors in which the anion binding is controlled by the complex formation of tetraester binding site with alkali metal cations in chloroform. 7 In these receptors, the amide moieties functioned as anion recognition sites through hydrogenbonding interactions.Thiourea moiety has also shown to be an effective binding site to recognize anions such as mono-and dicarboxylate, halide, sulfate, and dihydrogenphosphate anions through hydrogen-bonding interaction. [8][9][10][11][12][13][14][15] We have recently reported that selective colorimetry and fluorometry of anions are feasible by introducing chromogenic and fluorogenic transducers into the thiourea moiety with an electronically conjugated structure. [16][17][18] If the anion recognition is performed by solvent extraction, the function of these anion receptors would be applicable to various separation and sensing systems such as membrane transport and optode analysis. [19][20][21][22][23][24] To prove this feasibility, we report herein an efficient synergistic effect of a thiourea receptor for an ion-pair extraction of potassium salts by dicyclohexyl-18-crown-6 (DC18C6) through hydrogen-bonding interaction. DC18C6 is well known as a specific binder for potassium cation. 25 In combination with the ion pair extraction of potassium salts by DC18C6, the extraction behavior of nitrate, bromide, chloride, and acetate ions from aqueous into nitrobenzene solution with a simple ion receptor, diphenylthiourea (DPTU), have been examined. Interestingly, the hydrophilic chloride ion is effectively extracted into the organic solution in the presence of DPTU. The importance of hydrogenbonding interaction for this extraction system is clarified by 1 H NMR analysis in the present study. ExperimentalReagents Diphenylthiourea receptor, DPTU, was purchased from Wako Pure Chemical Co., Ltd. DC18C6 was obtained from Tokyo Chemical Industry Co., Ltd. Science, Tohoku University, Aoba, Japan In combination with an ion pair extraction of potassium salts by dicyclohexyl-18-crown-6 (DC18C6), extraction behavior of anions with a diphenylthiourea (DPTU) from aqueous phase into nitrobenzene has been examined. The extraction selectivity of potassium salts follows a Hofmeister series: NO3 ->Br ->Cl ->OAc -. The extractability of KCl by DC18C6 is significantly enhanced upon the addition of DPTU in organic solution. The slope analysis of the extraction equilibrium reveals a 1:1 complex formation between DPTU and Cl -. The hydrogen-bonding interaction of DPTU with Cl -is confirmed by ...

Anion Separation with Metal–Organic Frameworks

“…These nearnormal Hofmeister systems thus lie in the lower left box in the selectivity model shown in Figure 2. Examples in liquid/ liquid extraction include diphenylurea [45] and m-diphenyldisulfonamides, [20,46] though peak selectivity for iodide has been claimed for monothiouronium receptors.…”

A Multi‐Element Ion‐Pair Extraction for Trace Metals Determination in Environmental Samples

“…Ion‐pair recognition of cationic and anionic guest species by bifunctional receptors is a current topic in molecular recognition chemistry 6. In ion‐pair extractive separation of metal cations using a complexation reagent and a counter anion is one of the most important factors to realize their mutual separation.…”

The effect of the counter anion on the transport of thiourea in a PVC-based polymer inclusion membrane using Capriquat as carrier

“…This provides strong evidence that the extraction of thiourea with the TOMA ion-pairs studied takes place via the formation of a heteroconjugate anion. Other reports support this conclusion since they have shown that anions can interact with thiourea or its derivatives through hydrogen bonding [9][10][11][12][13].…”

“…Interactions in organic solvents between uncharged organic molecules, acting as hydrogen bond donors, and small inorganic anions have been used successfully in analytical separation and sensing [7][8][9][10][11][12][13]. The formation of the corresponding heteroconjugate anions results in the stabilization of the small inorganic anions.…”

“…The formation of the corresponding heteroconjugate anions results in the stabilization of the small inorganic anions. Thiourea and its derivatives are well known for their anion binding properties leading to the formation of heteroconjugate anions [9][10][11][12][13]. It can be expected that the permeability of PIMs containing quaternary ammonium salts can be manipulated by varying the corresponding counter anion.…”