Effects of the anion on the extraction of zinc with 8-hydroxyquinoline into chloroform

Abstract

Zinc 8-hydroxyquinoline complexes are extracted into a chloroform phase as a mixture of two species. Which of the two is extracted predominantly into the chloroform phase depends primarily on the kind of anion in the aqueous phase. The species extracted from an aqueous phase containing nitrate, sulfate or chloride ion is predominantly the anhydride of the 1:2 zinc 8-hydroxyquinoline complex, ZnOx 2 which is so readily hydrated on the contact with water and precipitates as ZnOx 2·2H 2O. On the other hand, in the case of perchlorate, thiocyanate or iodide ion the extracted species is predominantly the ion-pair complex containing the respective anion. The extractability of these ion-pair complexes into a chloroform phase increases on the following order: ClO 4 − > I − > SCN − > Br − > Cl − ⪢ SO 4 2−.