Solvent extraction of sodium perrhenate by 3 m-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

Abstract

Equilibrium constants ( K MLA 0 / mo l − 1 d m 3 ) for the ion-pair formation of a complex ion NaL + with ReO 4 − 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, NaReO 4 was extracted by the L into 1,2-dichloroethane and then extraction constants ( K ex/mol −2 dm 6) for the species, NaLReO 4, 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.