Calix[4]arene-crown-5 as a selective extraction reagents for K${}^{+}$/H${}^{+}$, Rb${}^{+}$/H${}^{+}$ and Rb${}^{+}$/Cs${}^{+}$ separations

From extraction experiments, the exchange extraction constants corresponding to the general equilibriums M${}^{+}$ (aq) + NaL${}^{+}$ (org) ⇔ ML${}^{+}$ (org) + Na${}^{+}$ (aq) or M${}^{+}$ (aq) + CsL${}^{+}$ (org) ⇔ ML${}^{+}$ (org) + Cs${}^{+}$ (aq), which take place in the two-phase water–nitrobenzene extraction system (M${}^{+}$ = Li${}^{+}$, H${}_3$O${}^{+}$, Ag${}^{+}$, K${}^{+}$, NH${}_4$${}^{+}$, Tl${}^{+}$, Rb${}^{+}$; L = calix[4]arene-bis crown5(1,3- alternate), 26,28-dipropoxycalix[4]arene-crown-5(1,3- alternate), 11,23-dibromo-25,28-dipropoxycalix[4]arene-crown-5 (1,3- alternate) and 1,3- alternate -25,27-dihydroxycalix[4]arene-crown-5; aq = aqueous phase, org = organic phase), were evaluated. The stability constants of the NaL${}^{+}$ and CsL${}^{+}$ complexes were calculated from the extraction of the respective picrates in the system of water–nitrobenzene solution of L. Further, the stability constants of the ML${}^{+}$ complexes in nitrobenzene saturated with water were determined. High selectivities were found in some systems under study.