- Orgadc
2nd Annad Summer S g r n p o e i n ~ n
Reagents
Water-Soluble 1,2=Dioximes as Analytical Reagents ROGER C. VOTER AND CHARLES V. BANKS Institute f o r Atomic Research and Department of Chemistry, Iowa State College, Ames, Iowa The water-soluble 1,2-dioximes possess an advantage over reagents for nickel and palladium, such as dimethylglyoxime, which must be made up in organic solvents, where the danger of contamination of the nickel precipitate with excess reagent is always imminent. Discussed in this paper are the l,2-dioximes reported as being water-solublediaminoglyoxime, a-furildioxime, 1,2-cyclopentanedionedioxime, 1,2-~yclohexanedionedioxime, and 1,2cycloheptanedionedioxime. Only the latter two compounds are sufficiently soluble in cool water to allow them to be made up and used in aqueous solution at room temperature. 1,2Xycloheptanedionedioxime was found to be superior in many ways to the previously reported water-soluble 1,2-di-
A
8 OPPOSED to such reagents as dimethylglyoxime, the use of water-soluble 1,a-dioximes minimizes the danger of con-
taminating the nickel precipitate with excess reagent and avoids the solvent action of alcohol or acetone on this precipitate. I t is more convenient and economical to use a stable aqueous solution of a water-soluble reagent. Several attempts have been made to solubilize dimethylglyoxime and thus eliminate some of its disadvantages.
Kasey (8) recommended the use of a 2% solution, prepared by slowly adding a solution containing sodium hydroxide to hot water containing solid dimethylglyoxime. Semon and Damerell (17) describe the preparation of sodium dimethylglyoximate octahydrate by dissolving solid dimethylglyoxime in aqueous sodium hydroxide solution and then adding ethanol to precipitate the octahydrate. This preparation, of coursz, does not eliminate the use of an organic solvent. Hillebrand and Lundell (6) and Lundell, Hoffman, and Bright ( 1 1 ) suggest the use of ammonium hydroxide for solution of dimethylglyoxime when ethanol is not readily available. Such solutions are not stable for long periods of time (1). Raithel (13) recommended preparing the dimethylglyoxime reagent by thoroughly mixing equal weights of sodium peroxide and solid dimethylglyoxime and dissolving this mixture in distilled water followed by dilution. Diehl, Ilenn, and Goodwine (3) pointed out the explosive hazard of preparing the reagent solution as Raithel recommended and showed that decomposition of such a solution was even more rapid than that of a solution of dirnethylglyoxime in 1% sodium hydroxide. The need for water-soluble 1,2-dioximes is apparent, for none of the proposed schemes to solubilize dimethylglyoxime has eliminated the use of an organic solvent and a t the same time resulted in a stable aqueous solution of dimethylglyoxime DIAMINOG LYOXIM E
Diaminoglyoxime, called niccolos, has been proposed by Kuras (9, 10) as a reagent for the micro- and macrogravimetric determination of nickel. This reagent is easily prepared by reaction of cyanogen with hydroxylamine according to the procedure of Fischer ( 5 ) . Diaminoglyoxime, although soluble in hot water, is difficultly soluble in cold water and alcohol. The orangeyellow nickel compound, which contains 20.05y0 nickel, is soluble in acid but insoluble in slightly ammoniacal solutions. It does oot tend to creep and is stable toward drying. Nickel can be
oximes. This reagent reacts with nickel ions to form a yellow precipitate that can be used for the gravimetric determination of this metal. Quantitative precipitation is obtained at pH 2.7 and greater. Nickel may be determined in solutions containing acetate, tartrate, chloride, citrate, perchlorate, sulfate, sulfosalicylate, nitrate, and thiocyanate anions. Nickel is satisfactorily determined in the presence of aluminum, chromium, manganese, vanadium, lead, magnesium, zinc, cadmium, arsenic, antimony, beryllium, iron, titanium, molybdenum, cobalt, bismuth, and copper, and in several alloys. A rapid, direct method for determining nicked in steels containing both cobalt and copper is described.
determined in the presence of sulfate, chloride, nitrate, manganese. chromium, aluminum, zinc, and the alkali metals. However. the use of this reagent is definitely limited by the fact that iron and cobalt seriously interfere. ALPHA-FURILDIOXIME
Alpha-furildioxime was first reported by Tschugaeff (19) iu 1905 as one of twelve 1,Sdioximes found to form colored complexes with nickel. I t was not until 1925, however, that Soulr (18) described it as a water-soluble compound, suitable for analytical xork, and recommended it as a specific reagent for the detection and determination of nickel. A satisfactory method for preparing a-furildioxime from furfural has been worked out by Reed, Banks, and Diehl (16) The solubility of this reagent in water at room temperature waE found to be 0.79 gram (0.0033 mole) per liter (15),which is ver) nearly the same as the solubility of dimethylglyoxime-i.e.. 0.40 gram (0.0034 mole) per liter. However, a 2% solution can be prepared (18) in hot mater and used ahile hot. Other workers ( 1 5 ) have used a 2% solution of the reagent in 30% ethanol. A hich is stable a t room temperature for long periods of time. Reed and Banks ( 1 6 ) have shown that a-furildioxime can be used to separate nickel but they do not recommend its use for determining this metal because the nickel-reagent ratio in the nickel precipitate has been found to vary from 1: 2 to 1:l with increasing pH. The yellow palladium compound, which contains 19.57% palladium, is quantitatively precipitated over the pH range 0.2 to 6 and it filters satisfactorily. I t is stable toward drying and as much as 150% excess reagent has no noticeable effect on the results. Palladium can be satisfactorily determined in the presence of various anions and cations and can be effectively separated from platinum by a single precipitation. Alpha-furildioxime, although a satisfactory reagent for the separation and determination of palladium, leaves much to be desired as to solubility in water and as an analytical reagent for nickel. 1,2-CYCLOPEhTANEDIONEDIOXIME
l,%Cyclopentanedionedioxime, although soluble in water t o the extent of 1.3grams(0.01 mo1e)per liter, haa very little promise
1320
1321
V O L U M E 21, NO. 11, N O V E M B E R 1 9 4 9 an analytical reagent because of the very narrow pH range w e r which the nickel compound is insoluble. ds
1,2-CYCLOHEX.4NEDIONEDIOXIME 111 1924 Wallach ( 2 3 ) reported that 1,2-cyclohexanedioiit*lioxime, now called nioxime, yielded a scarlet precipitate with nickel and was a very sensitive qualitative test for nickel. Seven vears later Feigl ( 4 ) pointed out that this compound should br YII ideal reagent for nickrl. inasmuch as its solubility in water cvould constitute a significant advantage over dimethylglyoxime. It was not until 1945, hon-ever, that Rauh, Smith, Banks, and Diehl ( 1 4 ) succeeded in obtaining a sufficient amount of 1,2~.>-elohexanedionedioxime to make a detailed study of its proper.ies and uses as an analytical reagent. The solubility ul nioxime in nater a t 21.5' C. is 8.2 grams (0.058 mole) per liter Ir 17 times greater than the rorre.sponding molar solubility of ~iimethylglyoxime. Wcnger, Rlonnier, arid Rusconi ( 2 4 ) have used nioxime to ,ict,ermine nickel by a semiquantitative method based on the iniit of detection of the reaction. Voter, Banks, and Diehl (21) have shown that nioxime ea11 -atisfactorily be used for the gravimetric determination of nickel :n thc presence of man?- of the common anions and cations, prod e d an empirical factor is used to correct for the amount of axcess reagent that is carried down. Even though nioxime offers wveral advantages over dimethylglyoxime, such as watersolubility, increased sensitivity, quantitative precipitation down to pH 3, and a lower factor for nickel, its use as an analytical reagent for nickel is nevertheless limited because no single. precipitation method has been reported which makes it possible to determine nickel in the presence of iron. Sickel nioximt, precipitates are difficult to filter and the steps necessary to alleviate this trouble are time-consuming. Sioxime quantitatively precipitates palladium from solutions, the pH of x-hich are as low as 1, and has been shown to be satisfactory as an analytical reagent for this metal (22). In addition ro the advantages of water-solubility and increased sensitivity, ?he uw of niosime also makes possible a considerable saving of rime, because palladium nioxime can be filtered from a hot soluri(in after a brief digestion period. Johnson and Simmons (7) in 1946 showed that the color of riic.k(al niosime, stabilized with gum arabic solution, can be usetl SP thr, basis for a spectrophotomrtric method of deterniinirig riichpl i n steels.
1,2-CYCLOHEIYTASEDIONEDIOXIME
because niusime was found to possess some dktinct advitntages aver dimethylglyoxime as an analytical reagent for nickel and palladium, it was thought, that an investigation of the properties o f Pome of the higher homologs of 1,2-cyclohesanedionedioxim~ rniyht be worth while. In this connection, \-ander Haar, Voter, and Bttiiks (20) ,levised a method of preparing 1,2-~ycloheptanedionedioxime heptosime) from cycloheptanone. It was soon noted that this -ompound possessed characteristics which would make i t a :.ahable reagent for nickel, in that the previously stated dis:tdvantages elchibited by nioxime were not experienced with heptosime. Heptosime, which forms a yellow precipitate with niche1 ions, possesses almost all the good characteristics of both ,limethj.lglyosimeand niosime without their disadvantages. Presumably heptoxime reacts with nickel ions, as do other 1,2, iioximes, to give molecules of the resonance-stabilized square .npl:inar configuration. Physical Properties. Heptoxime, a white, crystalline solid with a molecular weight of 186.18, melts a t 179-180" C. when wcrystallizcd from water. By precipitating a measured volume of a saturated hcptoxime + ~ l i ~ t i nwith n an excess of nickel, the solubility of heptoxime in
water was found to be 4.8 grams (0.031 mole) per liter a t 19.5"C. Although this is somewhat less than the solubility of nioxime, it is still more than 9 times greater than the corresponding molar solubility of dimethylglyoxime. Reagents. A saturated aqueous solution of heptoxime waq used. A standard nickel chloride solution was prepared from Nond nickel obtained from the International Nickel Company (21), This solution was analyzed electrolytically and found to contain 0.001991 gram of nickel per gram of solution. All samples from this solution were measured by use of weight burets. The following solutions were made up by dissolving the reagentgrade chemicals in water: Citric acid solution, 1 gram per 3 rnl. of solution. Sodium sulfite solution, 1 gram per 10 ml. of dolution. Ammonium thiocyanate solution, 1 gram per 2 ml. of solution. Ammonium acetat,e solution, 1 gram per 5 ml. of solution. Gravimetric Determination of Nickel. Procedures for dettvmining nickel with dimethylglyoxime call for precipitation from neutral or mildly ammoniacal solutions (8). However, nickel heptosimc is best, precipitated from a slightly acid medium. This constitutes a distinct advantage, for nickel may be separated from certain cations without the use of complexing agents which would be needed under the pH conditions required for the quantitative precipitation of nickel nith dimethylglyoxime. Precipitation of nickel ions n i t h hrptosime was found to be quantita.tive tit pH values of 2.7 ur greater. The nickel lieptosime precipitate is of such a character that quantitative operations are easily performed. It does not tend ro creep as does nickel dimethylglyoxime. Nickel heptoxime was dried for as long as 5 hours a t 120" C. without apparent (leeomposition or loss of weight. ,4 series of determinations in which the amounts of nickel taken were varied indicated that samples of nickel from 6 to 61 mg. could be determined successfully (Table I). The solution volume was 200 ml. for each sample except determination 5 . where a larger volume was required because of the voluminous rharacter of the prrcipitate. The results of several determinations in which the per cent excess of heptoxime as varied are shown in Table 11. It i p apparent that excess reagent does not noticeably affect the results. Evidence obtained indicates that the presence of ammonium acetate helps prevent adsorption of excess reagent by t h P nickel heptoxime. The effect of various anions on the determination of nickel was studied. These anions, added as their ammonium salts or as the respective acids, \yere found not to interfere in the determinittion of nickel. Typical results are shown in Table 111.
Table I.
Determination of Nickel Wcight Of
Sickel Taken
Detn.
Gram
a
Precipitate Gram
Xickel Found
iclg.
1 0.0063 0,0400 0.0064 0.0878 0.0140 2 0,0135 0.1421 0.0226 3 0.0225 0.2168 0.0345 4 0.0345 0.3866 0.0615 5" 0.0614 Solution containing samplc di1;ited t o 600 ml.
Table 11.
Detn
+0.1 +o. 1 $0.1 0.0 f0.1
Effect of Excess Heptoxinie on Determination of Nickel Excess Heptoxinw Addeda
Sickel Taken
Weight of Preciuitate
Nickel Found
?%
Dram
Cram
Gram
0,0235 0.1486 0.0241 0.1521 0,0242 0.1525 0.0261 0.1648 0.0232 0.1468 5 150 2 grams of ammonium acetate also present.
1 2 3 4
Error
Gram
30 50 80 100
0.0236 0.0242 0.0243 0.0262 0.0233
Error ~\f!3. fO.l
to.1 +O.l f0.1 +o. 1
ANALYTICAL CHEMISTRY
1322 Table 111. Effect of Various Anions upon Determination of Nickel Anion Present Acetate Tartrate Chloride Citrate Perchlorate Sulfate Sulfosalicylate Nitrate ‘Thiocyanate
Anion Grams 1.6 9.0 1.4 2.0 1.8 1.5 2.0 1.7 1.5
Nickel Taken Gram 0.0224 0.0222 0.0236 0,0235 0,0243 0.0234 0.0259 0,0224 0.0218
Weight of Precipitate Gram 0.1408 0,1397 0.1495 0.1483 0.1525 0.1484 0,1625 0.1406 0.1375
Kickel Found Gram 0,0224 0,0222 0,0238 0.0236 0,0213 0.0236 0,0258 0.0224 0.0219
Error hlg. 0.0 0.0 +0.2 +O.l 0.0 f0.2
-0.1 0.0 +0.1
Nickel was determined in the presence of aluminum, chromic, manganous, vanadate, plumbous, magnesium, zinc, cadmium, antimonite, arsenite, beryllium, ferric, titanous, cuprous, cobaltous, molybdate, and bismuth ions. Bluminum, chromic, antimonite, arsenite, ferric, titanic, and bismuth ions, when present, must be complexed with either tartrate or citrate to prevent their coprecipitation as hydroxides. Cobaltous ions react with heptoxime to form a brown comples compound which remains in solutions if the cobalt concentration is not too high. However, if an appreciable amount of cobaltous ion is present, a reprecipitation may be necessary. Enough heptoxime must be added not only to precipitate the nickel but also to complex the cobaltous ions. Copper ions react with heptoxime, yielding an insoluble brown precipitate. However, this interference is eliminated by taking advantage of the fact that cuprous thiocyanate is soluble in excess thiocyanate (25). The soluble complex formed effectively masks the cuprous ions and prevents their reaction with heptoxime. Acetate is added to prevent the precipitation of plumbous chloride when lead is present. These data are shown in Table IV.
Table IV.
Ion Present Aluminuma Chromica Manganous Vanadate Plumbousb M;y%iumj
Effect of Various Metal Ions on Determination of Nickel
Ion Gram 0.2 0.2 0.3 0.3 0 ,05
0 . 2 each Cadmium ~ _ _ ~ $ ~ ~ $ t e h ] 0 . 3 each Beryllium 0.2 1.0 Ferrica 0.1 Titanice Cuprousd 0.01 0,007 Cobaltous 0.2 Molybdate 0.1 Bismutha
Nickel Taken Gram 0.0241 0.0251 0.0242 0,0240 0.0233
Weight of Precipitate Gram 0.1517 0.1580 0.1522 0.1616 0.1474
Sickel Found Gram 0.0241 0.0261 0.0241 0,0241 0,0234
0.0224
0.1416
0.0225
$0.1
0.0224 0.0219 0.0231 0,0215 0.0202 0.0213 0.0244 0,0230
0.1408 0.1395 0.1461 0.1365 0.1273 0.1356 0.1546 0.1459
0.0224 0,0222 0,0232 0,0217 0.0202
0.0 +0.3 +0.1 1-0.2
Error Mg.
0.0 0.0 +0.2 +0.1 +0.1
solutions being added to the sample solution. If lead is known to be present add 5 ml. of ammonium acetate solution. Add 10 ml. of sodium sulfite solution. After diluting the solution to 200 ml. adjust the pH to about 3.5 with ammonium hydroxide. Warm the solution to about 50” C. and add 20 ml. of ammonium thiocyanate solution. Stir until any precipitate of cuprous thiocyanate dissolves. For samples high in copper content, an additional 10 ml. of ammonium thiocyanate solution may be needed to dissolve this precipitate. As soon as the solution is clear, slowly add ~ i t constant h stirring 15 ml. of saturated heptoxime solution for each 10 mg. of nickel present plus 5 ml. in excess. Digest a t about 80 O C. for 10 minutes. Allow the beaker to stand in cool tap water for 30 minutes. Filter the solution through a weighed filter crucible of medium porosity, keeping the crucible filled with liquid. mash with cold water and dry a t 110” to 120” C. for at least 1 hour. The factor for nickel is 0.1590. I t is important that the pH be adjusted to about 3.5 before addition of the ammonium thiocyanate in order to prevent the formation of insoluble perthiocyanic acid (12). This procedure can readily be adapted for determining nickel in the presence of any of the metallic ions shown in Table IV. The metallic ions present determine the complexing agents that must be used. Khen tartrate or citrate is not used, 5 ml. of the ammonium acetate solution should be added to buffer the solution. I n most cases, a solution volume of about 200 ml. and a pH of about 4.0 are preferable.
Table V.
Determination of Kickel in Steel and an Aluminum Alloy Nickel Present
Material N.B.S. cast iron No. 115
Nickel Found
Found
%
%
%
15.89
15.82 15.93 15.94 15.84 9.29 9.26 9 . 23a 9.28’= 3.25 3.26 3.27
K.B.S. 18 chromium-9 nickel steel Xo. lOlc
9.27
N . B . S . nickel steel KO.33c
3.28
N.B.S. nickel-molybdenum steel So. llla
1.75
Ab..
15.88 9.28 9.26 3.26
1.75 1.75 1.74b 1.75b 0.558
S.B.S. chromium-nickel-molyb0.563 denum steel S o . 139 0.556 X.B.S. aluminum-base alloy 0.41 0.42 No. 85, 0.42 a Analysis run by analyst unfamiliar with this procedure. b To these samples were added 5 mg. of Cu + - and 5 mg. of Co ples contained 22.5 and 24.5 mg. of nickel, respectively.
1.75 0.557
0.42
*.
Sam-
~~
0,0216
0,0246 0,0232
0.0 +0.3
i-0.2 +0.2
Recommended Procedure. The following procedure is for the determination of nickel in iron and steel containing both cobalt and copper. Weigh a sample that contains approximately 20 mg. of nickel into a 500-ml. Erlenmeyer flask, and dissolve the sample in an appropriate acid or acid mixture. Decompcse any carbides with 10 ml. of nitric acid. Add 10 ml. of 60% perchloric acid per gram of sample taken. After fuming begins, boil the solution for 15 minutes. Add 4 volumes of water and, after dissolving any salts, filter off the silica. Wash with 1% hydrochloric acid and then with water. To the filtrate add 18 ml. of the citric acid solution for each gram of sample taken plus 3 ml. in excess. Filter all
The recommended procedure for determining nickel in steels containing both cobalt and copper was tested on five Sational Bureau of Standards steels representing a wide range of nickel content. An aluminum-base alloy was also analyzed for nickel. The results shown in Table V attest the accuracy of this simple and direct procedure. Adaptation of this procedure, so that dimethylglyosime could be used as the precipitating agent, was unsuccessful, as nickel dimethylglyoxime is somewhat soluble in the presence of thiocyanate ions. ACKNOWLEDGMENT
The authors wish to thank Raymond C. Ferguson for hie assistance in performing some of the ana’yses with heptoxime. LITERATURE CITED (1) D i e h l , H . , “Applications of Dioximes t o Analytical Chemistry,” p. 20, Columbus, Ohio, G. Frederick S m i t h Chemical Co.,
1940. (2) IEid., pp. 30-1. (3) Diehl, H . , Henn, J . , and Goodwine, W. C . , Chemist-Analyst, 35, 76 (1946).
1323
V O L U M E 2 1 , N O . 11, N O V E M B E R 1 9 4 9 (4) Feigl, F., “Qualitative Analyse mit Hilfe von Tupfelreaktionen,” p. 73, Leipzig, Akademische Verlagsgesellschaft, 1931. (5) Fischer, E., Ber., 22, 1931 (1889). (6) Hillebrand, W. F., and Lundell, G. E. F., “Applied Inorganic Analysis,” p. 40, New York, John Wiley & Sons, 1929. (7) Johnson, W.C., and Simmons, M., A n a l y s t , 71,554 (1946). ( 8 ) Kasey, J . B., Chemist-Analyst, 18, 8 (1929). (9) Kuras, M., Collection Czechoslov. Chem. Communs., 12, 198 (1947). (10) Kuras, hl., .Ilikrochemie per. Mikrochim. A c t a , 32, 192 (1944). (11) Lundell, G. E. F., Hoffman, J. I., and Bright, H. A , “Chemical Analysis of Iron and Steel,” pp. 32, 281, New York, John Wiley & Sons, 1931. (12) McAlpine, R. K., and Soule, B. A., “Qualitative Chemical Analysis,” p. 466, New York, D. Van Nostrand Co., 1933. (13) Raithel, E. E., Chemist-Analyst, 35, 35 (1946). (14) Rauh, E. G., Smith, G. F., Banks, C. V., and Diehl, H., J . Org. Chem., 10, 199 (1945). (15) Reed, S. A , , and Banks, C.V., Proc.Iowa Acad. Sci., 55,267 (1948).
2nd Annual Summer Sumposium
(16) Reed, S. A., Banks, C. V., and Diehl, H., J . Org. Chem., 12, 792 (1947). (17) Semon, W. L., and Darnerell, V. R., “Organic Syntheses,” Coll. Vol. 2, p. 206, New York, John Wiley & Sons, 1943. (18) Soule, B. A,, J . Am. Chem. SOC.,47, 981 (1925). (19) Tschugaeff, L., Z. anorg. Chem., 46, 144 (1905). Voter, R. C., and Banks, C. V., J . Org. (20) Vander Haar, R. W., Chem., 14, 836 (1949). (21) Voter, R. C., Banks, C. V., and Diehl, H., ANAL.CHEM.,20, 458 (1948). (22) Ibid., p. 652. (23) Wallach, O., A n n . , 437, 175 (1924). (24) Wenaer. P. E., Monnier, D., and Rusconi, Y., A n a l . C h i m . A&, 1, 190 (1947). (25) Willard, H. H., and Furman, N.H., “Elementary Quantitative Analysis,” p. 446, New York, D. Van Nostrand Co., 1940. RECEIVED July 25, 1949.
Contribution 70 f r o m Iowa State College Instit u t e for Atomic Research, Ames, Iowa.
- Organic Reagents
Precipitation of Thorium from Homogeneous Solution Separation from Rare Earths of Monazite Sand with Tetrachlorophthalic Acid LOUIS GORDON AND C. H. VANSELOW, Syracuse University, Syracuse, N. Y . HOBART H. WILLARD, University of Michigan, Ann Arbor, Mich. The reaction between thorium salts and certain dicarboxylic acids such as succinic, phthalic, and tetrachlorophthalic, proceeds extremely slowly in aqueous solution at room temperature. A visible precipitate does not form for many hours, whereas a gelatinous precipitate is obtained if the solutions are at or near boiling. When a clear solution of thorium and a dicarboxylic acid are warmed to 70” to 85“ C., with continuous stirring, a thorium salt slowly
P
RECIPITATES obtained by the method of precipitation from homogeneous solution possess more desirable characteristics for analytical separations than do those obtained by the conventional procedure. The method has been successfully employed for the determination of aluminum ( 8 ) , gallium (4), thorium ( 6 ) , zirconium ( 7 ) , and magnesium ( I ) , and for the separation of zirconium and hafnium ( 5 ) . For effecting the separation of thorium from the rare earths, two dicarboxylic acids have been reported in the literature as juccessful. The fumaric acid method ( 2 ) separates thorium from the rare earths in 40% ethanol as a white flocculent precipitate. Sebacic acid ( 3 ) is described as effecting this separation by precipitating thorium in a granular and voluminous form, but it is the experience of the authors that the product is too gelatinous. In neither method was less than 50 mg. of thorium oxide quantitatively precipitated. The precipitation of thorium from homogeneous solution rmploying a dicarbosylic acid appeared to offer several advantages-formation of a dense granular precipitate, separation from the rare earths, separation of small quantities of thorium, and weighing of the precipitate as the thorium salt without recourse to ignition to thorium oxide n-hich practically every gravimetric method requires. Only the first three of these objectives were attained. Tetrachlorophthalic acid and the other dicarboxylic acids that were studied seem to precipitate thorium in the method which is described here by a merhnnism quite different from the case
precipitates in a dense, crystalline, and readily filterable form. Tetrachlorophthalic acid is the only one studied which quantitatively precipitates thorium. Upon double precipitation at pH 1.0 to 1.2, this acid effects quantitative separation of thorium from the large amounts of rare earths normally found in monazite sand. This precipitation is accomplished by a relatively simple procedure. The precipitate is ignited to the oxide.
where either urea (4,6 , 8) or an ester of oxalic acid (1, 6) is used. The hydrolysis of urea produces ammonia, which in turn results in an increase in hydroxyl ion necessary for precipitation. The hydrolysis of an ester of oxalic acid directly results in the production of the necessary precipitant. I n the method described in this paper, a solution of tetrachlorophthalic acid is added directly to the solution of thorium and rare earths. At room temperature, a visible precipitate does not form for several hours. When the solution is gently warmed to 70” to 85 O C., with mechanical stirring, the thorium salt slowly precipitates in a dense, crystalline, and readily filterable form. The exact mechanism of this precipitation from homogeneous solution has not yet been determined. It is probably due to the increased dissociation, with rise in temperature, of a complex of thorium with hydroxyl ion with concurrent precipitation of a thorium salt. Yarious treatments that are commonly used to induce precipitation from supersaturated states were of no influence in effecting precipitation of the thorium salt from cool solutions. PRELIRIINARY INVESTIGATIONS WITH DICARBOXYLIC ACIDS
Materials Used. Pure thorium and rare earth perchlorates were prepared as for the urea method (6). -411dicarboxylic acids rrere C.P. products. Succinic Acid. The addition of a hot succinic acid solution to a solution containing thorium resulted in a gelatinous precipitate which was converted on long digestion to a crystalline precipitate. The addition of a cool succinic acid solution to a cool solution containing thorium resulted in the slow production of a dense crystalline precipitate upon slow heating ant1 rapid stirring.
