Kinetics of Extraction of Palladium(II) with o-Xylylene Bis-(diethyldithiocarbamate) or 3-Mercapto-l, 5-diphenylformazan from Aqueous Chloride Medium

Abstract

The mechanism and rate of the extraction of palladium(ll) with o-xylylene bis(diethyldithiocarbamate) (o-XEDTC) or 3-mercapto-l, 5-diphenylformazan (dithizone, Hdz) into chloroform were described. The extracted palladium-(ll)-o-XEDTC was represented as PdCl2 (o-XEDTC). The rate of the extraction of palladium(ll) with o-XEDTC or Hdz from weakly acidic chloride medium can be represented as -d[Pd(II)]/dt=k1[PdCl2(H2O)-][Q]orgK-1DR+k2[PdCI42-]X [Q]orgK-DR, where Q represents o-XEDTC or dithizone and KDR is the distribution constant of the extradants between chloroform and water. The replacement of chloride ions and/or water molecules with these extradante should proceed through the formation of five coordinated square pyramidal intermediates, and the subsequent reaction of the release of chloride ions or/and water molecules. That the reactivity of o-XEDTC toward PdCl2(H2O)4-n(2-n)+ is smaller than that of dithizone may be related to a steric effect on the formation of a five coordinated intermediate. Palladium(ll) was separated with o-XEDTC from other metal ions as copper(ll), zinc(ll), nickel(ll) and cobalt(ll). The interference of iron(lll) can be masked with phosphate or pyrophosphate.