Determination of Some Component Equilibrium-Constants by Cd(II) Picrate Extraction with Benzo-18-crown-6 Ether into Various Diluents and their Evaluation

Using benzo-18-crown-6 ether (B18C6), extraction experiments of cadmium picrate (CdPic2) into various diluents were performed at 298 K. Thereby, three kinds of extraction constants, KCd/CdL, Kex± and Kex, four kinds of distribution constants, KD,j (=[j]org/[j]), with j=Pic−, CdLPic2, CdLPic+ and CdL2+ and two kinds of ion-pair formation constants, K1,org {=Kex±/KCd/CdL(KD,Pic)2} and K2,org (=Kex/Kex±), for L=B18C6 were determined. Here, KCd/CdL, Kex± and Kex were defined as [CdL2+]org/[Cd2+][L]org, [CdLPic+]org[Pic−]org/P and [CdLPic2]org/P, respectively, with P=[Cd2+][L]org[Pic−]2 and the subscript “org” denotes an organic phase. Based on these equilibrium constants, distribution properties of the species j between the water (w) and org phases and reactivity of CdL2+ or CdLPic+ in the org phases were compared. Additionally, some Pb2+ selectivity coefficients, kpotPbCd(=KCd/CdL/KPb/PbL), against Cd2+ with L=18-crown-6 ether at the nitrobenzene/w, 1,2-dichloroethane/w, o-dichlorobenzene/w and dichloromethane/w interfaces.