Abstract
Resins containing dibenzo-18-crown-6 (phiDB18C6) as anchor groups have been prepared according to the procedure suggested by Blasius and the total capacity, CT, determined by micro analysis. The effective capacity, CE, of phiDB18C6 towards the alkali-metal salts using water as reaction media was obtained from saturation experiments. The electrolyte concentration dependence of the distribution ratio of 1:1 electrolytes between phiDB18C6 and water at 298K was studied and the results used to determine the concentration range at which a maximum separation factor between two ions could be achieved. The rational equilibrium constant, log K'ex, corrected for activity in the solution phase and the derived apparent free energy change, DeltaG'ex for the process taking place when phiDB18G6 is equilibrated with an aqueous or non-aqueous solutions (s) of the different M+A- electrolytes as represented by are calculated. The results obtained clearly reflect the influence of the anions on the extraction of cations by the resin containing the macrocyclic ligand. For aqueous solutions of electrolytes containing a common cation and different anions the selectivity found is in the order Pi→SCN→I→Br→C1-. An enhancement of selectivity by a factor of 1.55x104, 8.91x103, 2.09x103 and 1.55x103 is found for the picrate salts relative to the chloride, bromide, iodide and thiocyanate, respectively. The heats associated with the interaction of phiDB18C6 and 1:1 electrolytes in aqueous solutions were measured calorimetrically at 298K and the apparent enthalpy change evaluated. Combination of the free energy and enthalpy changes yield the corresponding entropy changes. The contribution of the enthalpy and entropy terms to the free energy suggests that the process of extraction of 1:1 electrolytes from the aqueous I s solution to the resin phase is enthalpically controlled. An interesting relationship is obtained when values for the effective capacity of the resin towards the different 1:1 electrolytes are plotted against the apparent enthalpies(DeltaH'ex) obtained for the different electrolytes in water. Distribution data for the 1:1 electrolytes and phiDB18C6 were obtained in solvents such as N,N-dimethylformamide (DMF), propylene carbonate (PC), acetonitrile, (AN), methanol (MeOH) and water (H2O), in an attempt to evaluate the reaction media effects on the extraction of 1:1 electrolytes by these resins. Distribution ratios decrease in the order AN→PC→MeOH→DMF→H2O. Interaction between organic molecules in aqueous solutions (urea, thiourea, and phenol) and phiDB18C6 were also studied. Effective capacity measurements as determined by saturation experiments at 298K using thiourea and phenol indicate that the 1:1 organic molecule crown ether ratio obtained for the former compound is altered to a 4:1 ratio in the case of phenol. A possible mechanism based on hydrogen bond formation in the resin phase is suggested.