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

Yoshihiro Kudo Shoichi Katsuta

doi:10.4172/2157-7544.1000146

Abstract

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.

Highlights

From comparing the experimental log KD,Pic value with the log KS D,Pic one for only the high-polar NB system, an interfacial potential difference (∆φeq) at extraction equilibrium was evaluated, where the symbol, log KD,PicS, shows the log KD,Pic value standardized at Δφeq=0 V and 25°C
Compositions of extracted complexes were determined by plotting log (D/(Pic−)2) against log (18C6)o at o=BBz, oDCBz, DBE, NB, and Bz [1,2,3,4,11]
D refers to an experimental distribution ratio of Cd(II) into the o phases and the (Pic−) and (18C6)o values were calculated from Equations (3) and (2), respectively

Summary

Introduction

From comparing the experimental log KD,Pic value with the KS D,Pic one for only the high-polar NB system, an interfacial potential difference (∆φeq) at extraction equilibrium was evaluated, where the symbol, log KD,PicS, shows the log KD,Pic value standardized at Δφeq=0 V and 25°C. 18-Crown-6 ether (18C6) extracts CdBr2, cadmium picrate (CdPic2), or alkaline-earth metal picrates into various diluents [1,2,3]. In the previous study [1], the authors clarified that the extracted ion-pair complex, Cd(18C6)Br2, very weakly interacts with water molecules and the diluents ones and they suggested that another complex. It has been suggested that the latter ion-pair complex has a more polar structure than the former does [1]. Kinds of the diluents used for the CdPic extraction experiments with 18C6 were fewer, compared with kinds of the diluents for the CdBr2 extraction ones. Component equilibria which constitute overall extraction equilibria have been considered to be at least 6-10 ones [1,3,4]. Except for several studies of the M(II) extraction with dibenzo-18C6 into nitrobenzene (NB)

Methods

Results

Conclusion