Solvent Extraction of Cadmium Picrate by 18-Crown-6 Ether into Several Less-polar Diluents and Nitrobenzene: Re-evaluation of the Corresponding Overall Extraction Systems

TCadmium picrate (CdPic2) in water was extracted at 25°C by 18-crown-6 ether (18C6) into o-dichlorobenzene (oDCBz), bromobenzene (BBz), dibutylether (DBE), and nitrobenzene (NB). Their extraction constants (Kex and Kex±) were determined, where Kex and Kex± at L=18C6 were defined as (CdLPic2)o/((Cd2+)(L)o(Pic−)2) and (CdLPic+) o(Pic−)o/((Cd2+)(L)o)(Pic−)2), respectively. The subscript “o” denotes an organic phase, such as oDCBz and BBz. The same extraction constants were re-determined for a system with benzene. Also, individual distribution constants (KD,Pic=(Pic−)o/(Pic−)) of picrate ion Pic− into the above o phases were determined with the Kex determination. Properties for the CdPic2 extraction with 18C6 were discussed by using the above constants and those available from the same extraction systems with other diluents. From comparing the experimental log KD,Pic value with the log KD,Pic S one for only the high-polar NB system, an interfacial potential difference (Δφeq) at extraction equilibrium was evaluated, where the symbol, log KD,Pic S, shows the log KD,Pic value standardized at Δφeq=0 V and 25°C. In the course of this study, an extraction constant for an HPic extraction into DBE was determined spectrophotometrically at 25°C.