Solvent extraction of sodium perrhenate by 3m-crown-m ethers (m = 5, 6) and their mono-benzo-derivatives into 1,2-dichloroethane: Elucidation of an overall extraction equilibrium based on component equilibria containing an ion-pair formation in water

Equilibrium constants (KMLA0/mol−1dm3) for the ion-pair formation of a complex ion NaL+ with ReO4− in water were determined potentiometrically at 25 °C and the ionic strength (I) of 0 mol dm−3 using a Na+-selective electrode. Here, crown ethers, L, were 15-crown-5 ether (15C5), benzo-15C5, 18-crown-6 ether (18C6) and benzo-18C6. Also, NaReO4 was extracted by the L into 1,2-dichloroethane and then extraction constants (Kex/mol−2 dm6) for the species, NaLReO4, were determined at 25 °C by AAS. These Kex values were resolved into four component equilibrium constants containing KMLA calculated at given I values. Based on these data, extraction-abilities of the L against the perrhenate were discussed in comparison with those of sodium picrate-L systems reported previously.