SCIENTlFlC C O M M UNICATION
Downloaded by UNIV OF NEBRASKA-LINCOLN on September 14, 2015 | http://pubs.acs.org Publication Date: April 1, 1956 | doi: 10.1021/ac50161a054
Gravimetric Determination Palladium(1 I) and Mercu ry(l I) as Bisethvlenediamine~alladium(lI> Tetraiodimercu rate(llj SIR: We have observed that milligram quantities of mercury(I1) or palladium(I1) may be precipitated quantitatively as bisethylenediaminepalladium(I1) tetraiodomercurate(II), [Pd(en)?]HgL. This precipitation is not influenced adversely by excess of the Precipitating reagent or most common anions and the precipitate is easily filtered and dried to constant weight. This salt is substantially insoluble in the pH range 6 to 8 and is only slowly attacked by hot concentrated nitric acid. These properties, together with the high molecular meight (935) and favorable gravimetric factor, suggcst the use of this precipitation for the gravimetric determination of either mercury(I1) or palladiuni(I1). M7e have established the applicability of this method to our own rather specific needs and have obtained uniformly satisfactory results. Limited studies on interferences indicated that precipitation with the tetraiodomercurate(I1) ion may prove useful for the quantitative precipitation of complexes of other tiansitional metal ions. Reagents. Bisethylenediaminepalladium(I1) bromide was prepared by fuming palladium(I1) nitrate or chloride to dryness several times with hydrobromic acid, heating this product with a slight excess of aqueous ethylenediamine, and precipitating the salt by the addition of a 10-fold volume of ethyl alcohol. The product was filtered, washed with absolute ethyl alcohol, and dried in vacuo at room temperature. Analysis. Calculated for [Pd(en),]Br2: Pd, 27.6. Found (by the dimethylglyoxime method): Pd, 27.6. A 0.8052-gram sample of this product was dissolved in water to provide 100.0 ml. of solution, which was used as the standard palladium solution. Somewhat more concentrated (ca. 0.05M) solutions of this compound were used as a precipitation reagent. The standard solution of potassium tetraiodomercurate(I1) contained 0.3239 gram of mercury(I1) iodide and 1.0 gram of potassium iodide in 100.0 ml. of solution; solutions ca. 0.09AI with respect to tetraidomercurate ion were used as precipitation reagents. Solutions of the following compounds were used in testing for cationic interferences: bisethylcnedianiineplatinum(I1) bromide (4), bisethylenediaminegold( 111) bromide (1), tetrammineplatinum( 11) bromide ( 6 ) , chloropentamminechromium( 111) chloride (j), bisethylenediaminecopper( 11)chloride ( 3 ) , and trisethylenediaminenickel( 11) chloride ( 2 ) . Determination of Palladium. Aliquots of the standard solution of bisethylenediaminepalladium(II) bromide solution were adjusted to pH 6 to 8 and treated dropwise with potassium
Table I. ,
d, A .
7.80 0.43 4.94
4.63 4.25 3.99 3.73 3.48 3.23 3.08 2.88 2.77 2.68
X-Ray Diffraction Data for Bisethyletierliaiiiixiepalladium(I1) Tetraiodonierc~irate(I1)” 1/10 0.9 0.7 0.1 0.8
0.7 1.0 0.7 1.0 0.1
0.7
0.1 0.8 0.2
d, A.
1/10 0.2 0.0 0.4 0.2 0.2
0.5 0.4 0.3 0.2 0.2 0.2 0.4
d, A . . 69 .66
.GI
.51 .47 .45 .42 .38 .34 .28 .24 23 .13
1/10 0.1 0.4 0.3 0.4 0.3 0.3 0.1 0.1 0.1 0.2 0.1 0.1
0.1
From pattern obtained using CuKor rndiation, 15-ma. filament current, 35-kv.tube voltage, a n d exposure time of 0 hours. 0
tetraiodomercurate(I1) solution until no further precipitation mas evident. The precipitate was allowed to coagulate for about 10 minutes, filtered on a tared fritted-glass crurible, washed with distilled water, and dried to constant weight a t 115”. Thus, 1.0-, 3.0-, 5.0-, and 10.0-ml. aliquots containing, respectively, 2.22, 6.66, 11.10, and 22.20 mg. of palladium weie found by this procedure to contain 2.18, 6.64, 11.11, and 22.21 mg., respectively. The composition of the salt precipitated was further confirmed by ignition of a weighed sample to palladium(I1) oxide. Found: Pd, 11.7. Calculated for [Pd(en)>]HgIa: Pd, 11.4. Apparently the only precaution necessary is to ensure that the precipitate does not dry on the walls of the beaker, from vhich the precipitate is difficult to remove. Before biscthvlenediaminepalladium( 11) tetraiodomercurate( 11) is dried, it exhibits appreciable solubility in ethyl alcohol and acetone, but is substantially insoluble in these solvents after thorough drying a t 115”. X-ray diffraction data for this compound are given in Table I. Determination of Mercury. Aliquots (1.0, 5.0, and 10.0 ml.) of the standard potassium tetraiodomercurate(I1) solution were adjusted to pH 6 to 8 and treated with a slight excess of bisethylenediaminepnlladium(I1) bromide or iodide solution; the precipitates were treated as described above. These three aliquots contained 1.43, 7.15, and 14.3 mg. of mercury, as compared with 1.30, 7.06, and 14.2 mg. found, respectively. Interferences. Tests for possible interferences by common anions were carried out as follows: To 10 ml. of mater was added a quantity of hydrochloric acid such that the solution finally analyzed for palladium was ca. 0.05111 with respect to chloride ion. Bisethylenediaminepalladium(I1) iodide was dissolved in this solution, the pH was adjusted t o 7 to 8, and an aliquot was analyzed for palladium by the dimethylglyoxime method. Found: Pd, 18.3 mg. Another aliquot was analyzed by precipitation of bisethylenediaminepalladium( 11) tetraiodomercurate( 11) as described above (found: Pd, 18.4 mg.), and the palladium content calculated from the data obtained by igniting this precipitate to palladium(I1) oxide was 18.4 mg. In strictly analogous experiments, the weights of palladium found in the presence of the following anions are: bromide 18.4, iodide 18.3, nitrate 18.5, sulfate 18.4, and perchlorate 18.5. That the precipitates obtained in these experiments did not contain anions other than the tetraiodomereurate( 11) ion was confirmed by means of x-ray diffraction patterns. Accordingly, it may be concluded that the common anions do not interfere with this precipitation. Similar tests for interferences by transitional metal cations show that bisethylenediamineplatinuni(II), tetrammineplatinum(II), bisethylenediaminegold(III), chloropentamniinechromium(III), bisethylenediaminecopper(II), and trisethylenediaminenickel( 11) ions interfere and must therefore be removed prior to the precipitation of either palladium or mercury. Both of the platinum(I1) complexes apparently precipitate as the ditriiodomercurate(I1) salts, although under other conditions the tetraiodomercurates may also be obtained. Preliminary results also suggest that interferences by complexes of copper(I1) and nickel(I1) may be obviated by carrying out the precipitation in somewhat more acidic solutions. Department of Chemistry, T h e University of T e x a s , Austin 12, T e x .
GEORGE W. WATT DONALD 3’1.SOWAICDS ROBERT E. MCCARLEY
LITERATURE CrTED
(1) Block, B. P., Bailar, 3. C., Jr., -1.Am. Chem. SOC.73. 4723 (1951).
(2) Bucknall, Wr.R., Wardlaw, W., J . Chem. SOC.1928,2739. (3) Chattaway, F. W., Drew, H. D. I
