Effects of the Anion on the Extraction of Cobalt with 8-Quinolinol into Chloroform

Abstract

Abstract The effects of the anions, especially the perchlorate ion, on the extraction of cobalt into chloroform with 8-quinolinol (Hql) were examined. Two kinds of cobalt(II) 8-quinolinol complexes, species A and B, are extracted into the chloroform phase from the aqueous cobalt(II) solution containing perchlorate ions. Species A contains no perchlorate ion and is extracted above pH 7.7; species B is an ion-pair complex containing a perchlorate ion and is predominantly extracted below pH 5.1. The compositions of species A and B were estimated to be Co2ql4(Hql)2 and Co2ql3(Hql)3ClO4, respectively. These dimer complexes are related by the following equilibrium, with logKAB=−7.2: [Co_2ql_3(Hql)_3]^+ClO_4(o)^-\ightleftarrowsCo_2ql_4(Hql)_2(o)+ClO_4^-+H^+ The species extracted into the chloroform phase from the aqueous cobalt(II) solution containing sulfate ions does not contain any sulfate ions. The formation of the species containing anions increases in the order: ClO4−>NO3−>Cl−>So42−, which is also the general order of the extent of forming the ion-pair compounds. The ion-pair complex tends to prevent the oxidation from cobalt(II) 8-quinolinol complex to cobalt(III) 8-quinolinol complex.