ANALYTICAL EDITION
April 15, 1942
of diethylstilbestrol. Presumably the bromination product contains seven atoms of bromine. Studies made with 4,4'dihydroxystilbene indicate that four Of these are located in the 3,5- and 3',5'-positions. It would be expected that simultaneously two atoms of bromine would add at the double bond. The splitting out of one of these bromine atoms as hydrogen bromide would provide a vinylene linkage into enter. The diagram tmo more bromine atoms appears to explain the data in the most satisfactory manner.
359
Literature Cited (1) Dechne, C. B., J. Am. Pharm. Assoc., 30, 208-9 (1941).
(2) Dod&, E. C., Goldberg, L., Lawson, W., and Robinson, R., Nature, 141, 247 (1938). (3) Francis, A. W., and Hill, A. J., J. Am. Chem. Soc., 46, 2498 (1924); IND.ENG.CHEM.,ANAL.ED., 13, 357 (1941). (4) Sprung, Jf. M.,Ibid., 13, 35 (1941). PRESENTED before the Division of Medicinal Chemistry a t t h e 102nd hleeting of the h V E R 1 C A N CHEDIIC4L SOCIETY, ~ t ~ a n t City, ic N. J.
Separation of Copper, Lead, and Zinc with Salicvlaldoxime J
L. P. BIEFELD AND W. B. LIGETT Purdue University, Lafayette, Ind.
T
HE separation of copper from other metals which form
complexes with salicylaldoxime is possible because copper salicylaldoximate may be precipitated in weakly acidic solutions, whereas the salicylaldoximates of most other metals are precipitated only from neutral or slightly basic solutions (1-6, IO). Lead has been separated from silver, zinc, and cadmium by precipitation in strongly ammoniacal solution (7). The effect of hydrogen-ion concentration upon the precipitation of zinc with salicylaldoxime has been reported briefly ( 5 ) . The purpose of the present investigation was to make a more detailed study of the effect of p H on the precipitation of zinc salicylaldoximate, and to determine the best conditions for a separation of copper, lead, and zinc based upon p H control and ammonia-complex formation.
Precipitation of Zinc Salicylaldoximate The fact that zinc forms a n insoluble complex with salicvlaldoxime was first reported by Ephraim studied the properties of the precipitate and concluded that it was not suitable for the quantitative determination of zinc because the p H range for complete precipitation was too narrow, the precipitate was appreciably soluble in various neutral salt solutions, and the compound slomly decomposed above 80" C. The compound precipitated by Pearson contained 19.45 per cent zinc by analysis and which contains evidently mas Zn(C7H602S)2, 19.36 per cent zinc. Flagg and Furman (5) found that if zinc salicylaldoximate, together with the solution from which it has been freshly precipitated, is warmed to 90" C. for 10 minutes, a compound corresponding t o Zn(C;H602N) results. This compound, containing 32.61 per cent zinc, can be dried at 110" C. without decomposition. Since the compound obtained by Flagg and Furman is obviously more suitable for quantitative purposes, the work described below is based upon precipitation of the compound Zn(CiH50zS).
(e).
REAGENTSAND APPAR.4TvS. The salicylaldoxime used was obtained from the Eastman Kodak Company. A 1 per cent solution was prepared bv dissolving 1 gram of the reagent in 5 ml. of alcohol and slomly pouring the alcohol
solution into 95 ml. of water warmed to 80" C. The reagent solution was cooled and filtered before use. The zinc solution was prepared from reagent grade zinc nitrate. It was standardized by precipitation and weighing as Zn?\'H4P04,and by precipitation as ZnSH4P04and ignition to ZnPZOr. , A glass electrode pH meter as described by Mellon (8) was used. I t was calibrated with Clark and Lubs buffer solutions. The reagents used in standardization of the zinc solution, those used in preparation of the buffers, and the ammonia used for adjustment of pH were all of reagent grade. Calibrated weights and volumetric ware were used. Redistilled water was employed for the preparation of all solutions, for dilutions, and for washing the precipitates. PRECIPITATION AND pH MEASUREMENT. In each case, 25 ml. of a 1 per cent salicylaldoxime solution were added dropwise to 25 ml. of zinc solution containing 0.0999 gram of zinc and ammonia in an amount estimated to give the desired pH. Water was added to make 100 ml. The mixture was mechanically stirred during addition of the reagent. After all the reagent had been added, solution and precipitate were heated to about 90" C. for 10 minutes, cooled to room temperature, filtered with suction on KO.4 Jena glass crucibles, washed with water, and dried a t 110" C. for 1 hour. Ferric chloride solution was used to test for complete washing of the precipitate, thorough washing
PH FIGURE1. PRECIPITATION OF COPPER, LEAD,ASD Zrsc
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INDUSTRIAL AND ENGINEERING CHEMISTRY
being indicated by the absence of coloration in a final portion of filtrate. The pH measurement was made upon the filtrate before the addition of any wash water. pH RAXGEFOR PRECIPITATION. The theoretical factor 0.3261 for zinc in Zn(C7H&O2N)was used in calculating the results which are presented in Figure 1, curve 3. As shown by the curve, the precipitation of zinc salicylaldoximate is complete only in the p H range 7.1 to 8.1. It is completely soluble below pH 5.8 and above pH 9.7 if the pH is regulated with ammonia.
Separation of Copper and Lead Curves 1and 2, Figure 1, reproduced from papers by Biefeld and Howe (2) and Ligett and Biefeld (7), respectively, show that the separation of copper from lead by precipitation with salicylaldoxime may be effected easily by control of the pH. The adjustment of the p H is usually made with acetic acid. Hydrogen ion is formed by the reaction between the metal ion and the reagent, and if a considerable amount of copper is present the hydrogen-ion concentration may be so increased that precipitation of copper will be incomplete (2). The simplest procedure is to buffer the solution with acetate ion. However, this is not satisfactory if it is desired to determine lead in the filtrate by precipitation with salicylaldoxime because the lead complex is appreciably soluble in acetate solutions (6). It was found that the correct pH could be readily attained by the use of modified methyl orange as indicator. After the addition of reagent to the solution of copper and lead, one or two drops of indicator were added. Then the solution was neutralized with ammonia, finishing with 0.5 M ammonia added dropwise with stirring. After standing for a few minutes, the supernatant liquid again shows the acid color of the indicator. This is due to the fact that the precipitation reaction does not immediately reach equilibrium after neutralization and a small additional amount of hydrogen ion is formed as the reaction goes to completion. It was unnecessary to bring the solution back to the neutral point again,
Separation of Lead and Zinc Curve 2, Figure 1, is reproduced from a previous paper of the authors (7). Together with curve 3, it indicates why a separation of lead from zinc is possible in highly ammoniacal solution, although considerably more ammonia is required to prevent the precipitation of zinc with lead than would seem to be necessary. Attempts were made to precipitate zinc from the filtrate after the separation of lead from zinc in highly ammoniacal solution. Neutralization of the large excess of ammonia present and the addition of salicylaldoxime did not result in the precipitation of zinc salicylaldoximate. Evidently the high concentration of ammonium salts present after neutrdi&ion of the ammonia acts to prevent the precipitation. Removal of the excess ammonia in the filtrate by boiling the solutions was attempted. Prolonged boiling resulted in precipitation, but the precipitate formed was light brown in color and gave results only approximating the amount of zinc known to be present. In view of these negative results, it was concluded that salicylaldoxime was not suitable for the determination of zinc in the filtrate after the separation of lead from strongly ammoniacal solution. However, the fact that the high concentration of ammonium salts was so effective in preventing the precipitation of zinc salicylaldoximate suggested an improvement upon the previously presented method ('7) of separating lead and zinc. It seemed that a high concentration of ammonium salts might make i t possible to use a lower concentrat,ion of ammonia when attempting to separate lead and zinc
4
with salicylaldoxime. This would be desirable, because if too much ammonia is present in this determination, an appreciable amount of the lead is not precipitated, and if too little ammonia is present, zinc salicylaldoximate coprecipitates with the lead complex. The purpose of the experiments outlined below was to determine whether the permissible range of ammonia concentration in the separation of lead from zinc might be widened by the use of a high concentration of salts. REAGENTS AND APPARATUS. Lead and zinc solutions were prepared from the corresponding reagent grade nitrates. The lead solution was standardized by precipitation as the sulfate. The same care with reagents, volumetric ware, and weights was taken as in the precipitation of zinc salicylaldoximate, with the added precaution that the ammonium nitrate used was tested for insoluble matter. PROCEDURE FOR SEPARATION. A 12-ml. portion of 1 per cent salicylaldoxime was added to a solution containing 0.0398 gram of lead and 0.0400 ram of zinc. This is an excess of rea ent over that required k r the precipitation of both metals. $hen 5 grams of ammonium nitrate were added, followed by varying amounts of concentrated ammonia solution and water to make 65 ml. The precipitate was allowed to stand in contact with the solution, with occasional stirring, for 1 hour. It was filtered, washed with 20 per cent alcohol, and dried at 110' C. for 1 hour. The amount of lead was calculated from the wei ht of recipitate, using the factor 0.6053 for lead in Pb(GH68,N). !'he resu1ts:are given in Table I. TABLEI. Concd. NHI Added
.w.
SEPAR.4TION OF
LEADAND
(0.0358 gram of lead present) Precipitate Lead Found Found Gram Gram 0.0395 0.0400 0.0357 0.0357 0.0357 0.0398 0.0357 0.0358
ZINC
E rroi M g.
+o. 1 fO.2 -0.1 -0.1 -0.1
0.0 -0.1 0.0
DISCUSSION OF RESULTS. The data of Table I demonstrate that a wide range of ammonia concentrations will suffice to keep the zinc from precipitating and still permit complete precipitation of lead salicylaldoximate, provided a large amount of ammonium nitrate is present. In the absence of ammonium nitrate, however, concentrations of ammonia as low as those given are not adequate, and the permissible range of ammonia concentration is much less. The precipitate obtained in the presence of high concentrations of ammonium nitrate is very satisfactory with respect to ease of handling. Freshly precipitated, it is gelatinous, but during a period of about 30 minutes it gradually changes to a form which is easily filtered. The progressive change is readily apparent when three or four separate solutions are precipitated a t intervals of a few minutes.
Separation of Copper, Lead, and Zinc The procedure described is based upon the facts outlined above, and is intended to be applicable to solutions containing varying proportions of the three metals. SOLUTIONS.The copper solution was prepared from reagent grade copper nitrate, and was standardized by electrodeposition and by precipitation with salicylaldoxime. The lead and zinc solutions and the reagent solution were prepared as described above. PROCEDURE FOR ANALYSIS. Portions of the copper, lead, and zinc solutions were taken to give solutions with varying quantities of each metal. A 30-ml. portion of 1 per cent salicylaldoxime was added. The solutions were then made neutral t o modified methyl orange by the dropwise addition of 0.5 M ammonia solution, The resulting precipitate and solution were allowed
ANALYTICAL EDITION
April 15, 1942
361
complex is easily obtained by the use of modified methyl Copper Lead Zinc orange. The separation of PrePreMetal cipitate PreMetal lead from zinc in highly amMetal cipitate Netal ;\fetal cipitate Xetal present found found Error present found found Error present found found E r r o r moniacal solution is improved Gram Gram Gram .Ma. Gram Gram Gram Mg. Gram Gram Gram .\fa. by the addition of a large 0.0694 0,1896 0.0695 + 0 . 1 0.0 0.0597 0.0987 0,0597 0.0 0.0089 0.0471 0.0089 amount of ammonium ni0.0694 0.0694 0.1893 0 . 0 0 , 0 5 9 7 0.0986 0 . 0 0 . 0 0.0597 0,0469 0 , 0 0 8 9 o.oos9 trate. I n the presence of a 0.0 0.0926 0.2526 0.0926 0.0 0.0199 0.0329 0,0199 0.0 0.0312 0,1649 0,0312 0.0926 0.2527 0.0926 0.0 0.0199 0.0330 0,0200 + O . l 0.0312 0.1645 0.0311 - 0 . 1 high concentration of am0.0231 0.0633 0.0232 + 0 . 1 0.0796 0.1311 0,0794 - 0 . 2 0.0 0.0223 0.1177 0 , 0 2 2 3 0.0231 0.0631 0.0231 0.0 0 , 0 7 9 6 0.1313 0,0795 - 0 . 1 0.0 0.0223 0.1178 0.0223 monium nitrate, a wide range 0.0463 0.1259 0 , 0 4 6 1 - 0 . 2 0.0398 0.0656 0.0397 - 0 . 1 0.0 0.0446 0.2354 0 , 0 4 4 6 of ammonia concentration 0.0463 0.1258 0.0461 - 0 . 2 0.0398 0,0656 0.0397 - 0 . 1 0.0 0.0446 0 , 2 3 5 6 0,0446 may be used to prevent coprecipitation of zinc salicylaldoximate while still permitt o stand 0.5 hour, filtered on a Gooch crucible, washed with 20 ting complete precipitation of the lead. Zinc cannot be per cent alcohol, dried at 110’ C., and weighed as Cu(C7H802N)~. quantitatively precipitated as the salicylaldoximate in the The factor for copper is 0.1893. strongly ammoniacal filtrate from the lead separation. The filtrate was transferred t o a beaker and 0.7 gram of ammonium nitrate and 1.0 ml. of concentrated ammonia were added for each 10 ml. of solution. This resulted in precipitation of Literature Cited lead salicylaldoximate. After standin 1 hour, the precipitate (1) Azzarello, E., and Accardo, A., Ann. chim. applicata, 23, 483 was filtered on a Gooch crucible, washef with 20 per cent alcohol, (1933). dried at 110” C., and weighed as Pb(C7Hs02N). The factor for ( 2 ) Biefeld,’L. P., and Howe, D. E., IND. ENQ.CHEM.,AXAL.ED., Lead is 0.6053. 11, 251 (1939). Zinc was determined in the atrate by precipitation and weigh(3) Chambers, bl., Chemist-Analyst, 26, 52 (1937). ing as ZniTHIPO,. The results are given in Table 11. TABLE 11.
-
DETERMIX.4TIOX OF COPPER,
-
LEAD,AND
7
-
ZINC
(4) Ephraim, F., Ber., 63, 1928 (1930).
(5) Flagg, J. P., and Furman, N. H., IXD. ENO. CHEM..ANAL. E D . , 12, 663 (1940). (6) Ishibashi, M.,and Kishi, H., J . Chem. SOC.Japan, 5 5 , 1067
Summary Zinc salicylaldoximate begins to precipitate at pH 5.8, is completely precipitated in the range 7.1 to 8.1, and is again soluble above pH 9.7 if the pH is regulated with ammonia Copper, lead, and zinc in the same solution may be separated with salicylaldoxime by precipitating the copper in weakly acidic solution, filtering it off, and then making the filtrate strongly ammoniacal to cause precipitation of the lead complex. The correct pH for precipitation of the copper
(1934). (7) Ligett, W. B., and Biefeld, L. P., IND.ENG.CAEM.,. ~ N A L . ED., 13, 813 (1941). (8) Mellon, M.G., “Methods of Quantitative Chemical Analysis”, p. 413, N e w York, Macmillan Co., 1937. (9) Pearson, Th. G., 2. anal. Chem., 112, 179 (1938). (10) Riley, H. L., J . Chem. SOC.,1933, 895. PREEENTED before t h e Division of Analytical a n d Micro Chemistry a t t h e CHEMICAL SOCIETY,Atlantic City, N . J . 102nd Meeting of t h e AMERICAN
Color Reactions of Organic Nitrogen Compounds with Selenious Acid- Sulfuric Acid Solution BARTLETT T. DEWEY’
AND
ALBERT H. GELRIAN, North Pacific College of Oregon, Portland, Ore.
S
ELENIOUS and selenic acids were proposed as reagents for the identification of the opium alkaloids by Brandt ( I ) , Lafon (S),and Ferreira da Silva (2). Mecke (6) observed the colors produced on the addition of a 0.5 per cent solution of selenious acid in concentrated sulfuric acid to the opium alkaloids, and recommended this solution as a reagent for the identification of minute quantities of these compounds. Levine (4) observed the color reactions of phenols and phenolic ethers with selenious acid-sulfuric acid reagent. He stated that the color production is a specific test for phenolic hydroxyl groups. The production of colored compounds he attributed to the oxidizing action of selenious acid, and he stated that a red or red-brown precipitate accompanying or following the primary color reaction is due to the reduction of selenious acid with the liberation of elemental selenium. Levine concluded that a positive reaction cannot be accepted as indicative of the presence of the opium alkaloids unless other phenolic compounds are absent. The present work reports the color reactions of some organic nitrogen compounds with selenious acid-sulfuric acid solution. I
Present address, 1704 Cascade Ave., Boulder, Colo.
Experimental One milligram of the compound was placed on a spot plate and a drop of a 0.5 per cent solution of selenious acid in concentrated sulfuric acid was added. Chemicals used were Eastman grade supplied by Eastman Kodak Co., Rochester, N. Y., and c. r, quality of the Pfanstiehl Chemical Go., Waukegan, Ill. To determine if the reaction is characteristic of the selenious acid reagent, a similar test was carried out simultaneouslywith sulfuric acid. The color changes which took place during a 3-hour period are recorded in Table I. Some compounds produced the same color in the sulfuric acid as in the selenious acid-sulfuric acid solution: benzidine, o-bromoaniline, m-bromoaniline, p,p’-diaminodiphenylmethane, dibenzylamine, diphenylnitrosoamine, diphenylthiocarbazone, methyl-o-toluidine, methyl-m-toluidine, methylp-toluidine, p-nitroaniline, p-nitrosodiphenylamine, m-phenylenediamine hydrochloride, and p-phenylenediamine. The following compounds gave either a faint pink or no color a t all: allylthiourea, o-aminobenzoic acid, m-aminobenzoic acid, p-aminobenzoic acid, dl-a-amino-a-methylbutyric acid, d-arginine monohydrochloride, asparagine, barbituric acid, o-chloroaniline, p-chloroaniline, creatinine, I-
