Kinetics of Extraction of Palladium(II) with o-Xylylene Bis- (diethyldithiocarbamate) or 3-Mercapto-1, 5-diphenylformazan from Aqueous Chloride Medium

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The mechanism and rate of the extraction of palladium(II) with o-xylylene bis(diethyldithiocarbamate) (o-XEDTC) or 3-mercapto-1, 5-diphenylformazan (dithizone, Hdz) into chloroform were described. The extracted palladium- (II)-o-XEDTC was represented as PdCl₂ (o-XEDTC). The rate of the extraction of palladium(II) with o-XEDTC or Hdz from weakly acidic chloride medium can be represented as -d[Pd(II)]/dt=k₁[PdCl₃(H₂O)^-][Q]_orgK^-1_DR+k₂[PdCl₄^2-]× [Q]_orgK^-1_DR, where Q represents o-XEDTC or dithizone and K_DR is the distribution constant of the extractants between chloroform and water. The replacement of chloride ions and/or water molecules with these extractants 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 PdCln(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(II) was separated with o-XEDTC from other metal ions as copper(II), zinc(II), nickel(II) and cobalt(II). The interference of iron(III) can be masked with phosphate or pyrophosphate.