Abstract
ABSTRACT The extraction of rhenium(vii) with benzo-15-crown-5 (B15C5) and dibenzo-18-crown-6 (DB1SC6) into 1,2-dichloroethane was investigated. The presence of K+, NH4 + or Na+ in aqueous phase was necessary for the extraction. The study showed that the Re(VII) was extracted by forming ion-pair compounds of [M+(B18C6][Re4 -] and [M+ (B15C5)n][ReO4 −](M+= K+, NH4 +. and Na+; n = 1-2). Effea of cationic crown ether complexes on extraction of RcO4 - is discussed in terms of structure of extracted species. It was found that K+-B15C5 cation is the most efficient since K+ forms hydrophobic 1:2 complex readily with B1SCS. Equilibrium constants (Kex) and thermodynamic quantities for these extraction reactions were determined. The Kex values decrease in the sequences of K+ > NH4 + > Na+ and B15C5 > DB18C6. The thermodynamic measurement indicated that the extraction of ReO4 − with cationic B15C5 and DB18C6 complexes was enthalpy driven. The different extraction behaviors between anion species and alkali picrates are discussed.
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