Electrophoretic and chromatographic studies on the hydrolysis of lead(II) in presence of acetylacetone

Abstract

The Influence of acetylacetone (2,4-pentanedlone) on the formation of lead hydroxlde precipitate and lead lonlc species In aqueous solutlons was studled by high voltage electrophoresls and adsorption chromatography on fllter paper cellulose. The combination of these two technlques enables one to follow both the hydrolysls and complexlng of metal lonlc species even In appreclably complex systems. The experiments were performed In a wlde range of pH values and concentrations of lead nltrate In 0.5M sodium perchlorate solutlons. The concentratlons of acetylacetone varled from 0.01 to 0.5M. The precipitation dlagrams, pH vs. log concn of lead nltrate at constant concentratlons of acetylacetone, shows reglons where Pb2+ lonlc specles, lead catlonlc hydrolytlc specles, catlonlc, uncharged, and anlon-IC hydroxoacetylacetonato complexes, and uncharged acetylacetonate Pb( A~a c )~~, were found to exist.The combination of high voltage electrophoresis, adsorption chromatography on filter paper cellulose, and tyndallometry can be used for characterization of different metal ionic species in aqueous solutions. In our previous papers, we introduced the combination of these techniques for characterization of zinc, lead, and bismuth ionic and/or hydrolytic species in aqueous solutions (1-3). The composition of soluble zirconyl oxalato complexes in aqueous solutions of zirconyl chloride-ammonium oxalate was also investigated using potentiometric titration in addition (4).The work reported herein stresses the complexing influence of acetylacetone (2,4-pentanedione) on the hydrolysis of lead(I1) in aqueous solutions. EXPERIMENTALMaterials. Standard solution of lead(I1) nitrate and sodium perchlorate were prepared by dissolving Merck p.a. salts in doubledistilled water, and their concentrations were determined by the ion exchange technique (Dowex 50-X) ( 5 ) .Carbonate-free solutions of sodium hydroxide were prepared in the usual way (6) and standardized by acidimetric titration. Standard 1.OM acetylacetone solution was prepared by dissolving Merck p.a. acetylacetone in double-distilled water.For electrophoretic experiments, radioisotope tracer 210Pb (New England Nuclear Co., Boston, Mass.) was used.Procedure. The electrolytic systems lead nitrate-sodium perchlorate-acetylacetone-sodium hydroxide or perchloric acid were prepared by mixing (7) equal volumes of aqueous solutions of lead nitrate and solutions of sodium hydroxide of perchloric acid and acetylacetone in 1.OM sodium perchlorate. Twenty ml and 1500 ml of the solutions were prepared for tyndallometric determinations and electrophoretic measurements, respectively. The systems were incubated overnight at 20 "C in a water bath, and then the onset of precipitation was determined tyndallometrically (I, 8-1 I ). At the same time, the electrophoretic mobility of 210Pb was determined in each system (I, 4,121.To avoid radioactive spots of 210Bi, the radioautographs of spots of 210Pb were performed 30 days after electrophoresis (2). RESULTS AND DISCUSSIONThe results of tyndallometric...