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

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 the ¹H NMR analysis in d₅-nitrobenzene. For qualitative evaluation, solid-liquid extraction of KCl into d₅-nitrobenzene containing DPTU and DC18C6 has been examined by ¹H NMR analysis. Similar to the liquid- liquid extraction, an efficient synergistic effect of DPTU for the extraction of KCl is clarified.