Solvent extraction of permanganates (Na, K) by 18-crown-6 ether from water into 1,2-dichloroethane: elucidation of an extraction equilibrium based on component equilibria.
Ion-pair formation constants (K(MLA) mol(-1) dm(3)) of Na(+)- and K(+)-18-crown-6 ether (18C6) complexes with MnO(4)(-) in water (w) were determined potentiometrically at 25 degrees C. Simultaneously, extraction constants (K(ex) mol(-2) dm(6)) of the permanganates with 18C6 from w into 1,2-dichloroethane at 25 degrees C were obtained from the spectrophotometric determination of distribution ratios of the permanganates. These K(ex) values were divided into K(MLA) and other three component equilibrium constants and thereby extraction-selectivity and -ability were discussed in comparison with corresponding metal picrate-18C6 extraction systems reported before.
Ion-pair formation in water and extraction into benzene of 18-crown-6-sodium ion complex with nitrated phenolate ions
The elementary equilibria in the extraction into benzene of a 18-crown-6 (18C6)–Na+ complex with nitrated phenolate anions have been studied at 25°C. The 1:1 ion-pair formation constants in water of the phenolate anions with Na+ (KMA) and 18C6–Na+ (KMLA) were measured by potentiometry with a Na+-selective electrode. The overall extraction constants (Kex) were determined, and the KMLA and Kex values were used to calculate the distribution constants of the neutral 18C6–sodium phenolate 1:1:1 complexes. The KMA values of all the phenolates are nearly equal, regardless of their difference in basicity. The KMLA value is much larger for picrate than for 2,4- or 2,6-dinitrophenolate. Such trends of the ion-pair formation in water are consistently explained on the basis of the thermochemical cycle including the ion-pairing process in the gas phase. The Kex value decreases in the order, picrate⪢2,6-dinitrophenolate>2,4-dinitrophenolate. The highest extractability of the picrate ion is attributed mostly to its highest ion-pairing ability in water for the 18C6–Na+ complex. The difference in the extractability between the dinitrophenolate isomers depends entirely on the lipophilicity of the 18C6–sodium phenolate complexes.
Stabilities in Water and Transfer Activity Coefficients from Water to Nonaqueous Solvents of Benzo-18-crown-6–Metal Ion Complexes
Formation constants in water of 1:1 benzo-18-crown-6 (B18C6)–metal ion complexes and the B18C6 solubility in water were determined at 25 °C by conductometry or potentiometry with ion-selective electrodes and spectrophotometry, respectively. The selectivity sequences of B18C6 for metal ions in water are Pb2+>Ba2+>Sr2+>Ag+>K+>Tl+>Na+>Rb+. In each case of alkali and alkaline earth metal ions, the more closely a metal ion fits into the B18C6 cavity, the more stable is the B18C6–metal ion complex. Although the solvation power of water for an alkali metal ion is not the largest of all solvents, the formation constant of a given B18C6–alkali metal ion complex in water is by far the smallest of all solvents. The transfer activity coefficients (γ) from water to nonaqueous solvents of the B18C6–metal ion complexes were then calculated from the formation constants of the B18C6 complexes, γ values of B18C6 (obtained from solubilities of B18C6), and γ values of the uncomplexed metal ions. The γ value of B18C6 is large...