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 () 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 (K_ex/mol⁻² dm⁶) for the species, NaLReO₄, were determined at 25 °C by AAS. These K_ex values were resolved into four component equilibrium constants containing K_MLA 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.