Aspects of Substoichiometry: Palladium

Abstract

A detailed study has been carried out of the solvent extraction of the complexes formed by palladium with diethyldithiocarbamic acid and dithizone under substoichiometric conditions. The results of this study have been applied to the development of methods for the determination of palladium by neutron activation analysis and isotope dilution analysis. Under substoichiometric conditions, that is, where the metal is in excess of the chelating agent, palladium was found to form three complexes with diethyldithiocarbamic acid (HDDC); the normal complex, palladium diethyldithiocarbamate [Pd(DDC)2], and two ternary complexes, palladium chloride diethyldithiocarbamate [Pd.C1(DDC)] and palladium hydroxide diethyldithiocarbamate [Pd.OH(DDC)]. With dithizone (H2Dz), three complexes were also formed: primary palladium dithizonate (Pd(HDz)2], secondary palladium dithizonate [Pd.Dz], and palladium chloride dithizonate [Pd.C1(HDz)]. The formulae of these complexes have been verified by analysis, and their ultraviolet spectra examined. The extraction of palladium diethyldithiocarbamate, palladium chloride diethyldithiocarbamate, primary palladium dithizonate, and palladium chloride dithizonate into chloroform and carbon tetrachloride has been studied under a variety of conditions using radioactive tracer techniques. The partition coefficients and solubilities in both solvents have been measured. The extraction constants of palladium diethyldithiocarbamate and palladium chloride diethyldithiocarbamate into chloroform have been determined by competition with ethylenediaminetetraacetic acid and potassium cyanide, and hence the stability constants calculated. The stability constants of the cyanopalladate ion [Pd(CN)2-4] and the protonated ethylenediaminetetraacetic acid complex (H2PdY] have also been determined. Two highly selective radiochemical separation procedures have been developed and applied to the determination of traces of palladium in rocks, biological material, and platinum. The first involves the extraction of palladium diethyldithiocarbamate from a medium of 5N hydrochloric acid using a substoichiometric amount of cupric diethyldithiocarbamate in chloroform. Using this separation, amounts of palladium down to 10-8g have been determined by neutron activation analysis. The second involves the extraction of primary palladium dithizonate from a medium of 0.1N sulfuric acid and less than 0.01N chloride ion concentration using a substoichiometric amount of dithizone in carbon tetrachloride. Using this separation, amounts of palladium down to 3x10-9 g have been determined by isotope dilution analysis.