Extraction of Several Divalent Metal Picrates by 18-Crown-6 Ether Derivatives into Benzene: A Refinement of Methods for Analyzing Extraction Equilibria

Three kinds of extraction constants, K sub( ex), K sub( ex plus or minus ), and K sub( ex+), were evaluated from the improved model that the following three component-equilibria were added to a previously-proposed model for an overall extraction: ... and ... Here, K sub( ex), K sub( ex plus or minus ), and K sub( ex+) were defined as ... and ... respectively; the subscript "Bz" denotes benzene as an organic phase. The symbols correspond to M super( 2+) = Ca super( 2+) and Pb super( 2+), L = 18-crown-6 ether (18C6) and dibenzo-18C6 (DB18C6), and A super( -) = picrate ion. The ion-pair formation constant for ... at M super( 2+) = Pb super( 2+) in an aqueous phase was also determined at 298 K and ionic strength of zero by an extraction of HA into 1,2-dichloroethane and Bz with the presence of Pb super( 2+) in the aqueous phase. The K sub( ex) values re-evaluated from the present model were in agreement with those determined by the previous extraction model. Individual distribution constants of A super( -) into Bz were almost constant irrespective of kinds of M super( 2+) and L employed. Furthermore, the composition-determination method of the ion pairs, MLA sub( 2), extracted into Bz was re-examined. Similar analyses were performed in the SrA sub( 2-), BaA sub( 2-)18C6, and SrA sub( 2-)DB18C6 systems without considering the formation of MA super( +) in the aqueous phases.