m-Cresoxyacetic Acid as a Reagent for Thorium - Analytical Chemistry

m-Cresoxyacetic Acid as a Reagent for Thorium Separation of Thorium f r o m the Rare Earths of Monazite and from Cranium

.

31. \ E S K i T A R A M A N I A H , B. S. \ RAGAAV4 RAO, AhD C. L.4KSII1I-INi R 4 0 , Andhra C'nicersity, Raltair, S o u t h India

Procedure for Estimation of Thorium. Take 10 ml. of thorium solution in a 400-ml. beaker, add 10 grams of solid ammonium nitrate and 3 drops of Congo red solution ( l q ) ,and neutralize with ammonia. -1dd 8 ml. of 0.1 -Vnitric (or hydrochloric) acid, dilute to 100 ml., and t'hen boil. Remove the burner and add over a period of 5 minutes 100 ml. of a boiling 2% solution of VLcresoxyacetic acid with constant stirring. After all the reagent has been added, continue boiling for 5 minutes, then set aside for 1 hour. Filter through a 11-cm. Whatman S o . 41 filter and wash with a hot solution of 1 gram of the reagent and 10 grams of ammonium nitrate in 1 liter of water. Ignite to the oxide, cool, and weigh as Thos. On addition of rri-cresosyacetic acid to a neutral or slightly acid thorium solution, a white curdy precipitate separates, which is rather difficult to filter. When ammonium nitrate is present ( 5 grams for 100 ml. of solution) the precipitate is less flocculent, settles more rapidly, and is easy to filter through a JVhat'nian No. 41 filter. The washed precipitate was dried. to constant weight a t 105' C. Ignition of the dried residue to the oxide gave slightly differing values with different samples. I t s composition corresponds approximately to three acid groups to one of thorium together with three molecules of water. This naturally points to its being a basic salt. Ignition t o the oxide for weighing is thus necessary. The results are given in Table I.

111,; aeparation of thorium from the rat'e earths, particularly in Pi,evious work on t,he subject has I ~ e t ~critically n reviewed by TVillard and Gordon (11),who also dwrril)e :in elegant method lor the decomposition of monazite ant1 the wtimation of thorium therein. Reference may also he ni:itle to R later communication by Gordon, Vanselow, and JVillard ( 8 ) . Several reagents have been under investigation in this hhoratory (4,9, IO). Organic reagents present the advantage that the precipitate is voluminous and etiablc small quantities of t h t , ineta1 ion to be handled conveniently. ttdresoxyacetic acid, ~v1iic.his described here, gives with as little as 2.0 mg. of thorium oxide a precipitate large enough for easy handling. The pt'ecipitate has a varying composition and cannot be weighed directly, hut this difficulty is overcome by igniting to the oxide.

'ITmonazite, is of great interest.

SEPARATION OF THORIUM FRO31 RARE EARTHS

Materials Used. m-Cresoxyacetic acid was prepared in this laboratory from m-cresol by condensing it. with monochloroacetic acid in the presence of sodium hydroxide ( 3 ) and purified by thwe crystallizations from boiling water. The final product melted at 102" C. Ammonium nitrate was an analytical reagent supplied by the British Drug Houses, Ltd., Poole, England. Ten grams of tbe nitrate on ignition in a platinum dish left no n-eighable residue. Thorium nitrate was prepared as follows: Fifty grams of thorium nitrate (laboratory reagent 'c uality) were dissolved in 1 liter of water and acidified with 40 mi. of hydrochloric acid, and the thorium was precipitated hot with an excess of oxalic acid. The precipitate was allowed to settle overnight, filtered, and washed with 270 oxalic acid in 0.2 S hydrochloric acid. The precipitate was dissolved by digestion with concentrated nitric acid over a water bath. The solution was then evaporated on a water bath until the greater part of the nitric acid had been driven awiy, The liquid was dilut,ed to 1 liter and after addition of 30 ml. of hydrochloric acid, precipitation xith oxalic acid was repeated. The precipitate after complete washing was again dissolved in nitric acid. T o the hot nitrate solution was added sufficient 3Tchydrogen peroxide to precipitate the hydrous oxide of thorium. The precipitate was first washed with 3% ammonium nitrate solution and finally with hot water until free from nitrate. The wished residue was dissolved 11.v running hot 10% nitric acid through the filter several times. The clear solution was evaporated to dryness on a water bath. The residue was then dried for 40 hours in an air oven a t 105 i 2" C. A standard solution of thorium nitrate was prepared by dissolving t,he dried salt in water. Aliquots of this solution mere used in the following experiments. The thorium content of this solution mas determined by two independent methods-m-nitrobenzoic acid ( 6 )and sebacic acid (8) nhich yielded in 10 nil. of the solution 0.0884 and 0.885 gram of thorium oxide, respectively. Technical cerous oxalate from which RAREEAR'rii NITRATES. .other rare earths had not been removed was dissolved in nitric acid and the thorium was completely removed by two precipitations with hydrogen peroxide. The rare earth oxalates were then precipitated with oxalic acid. The residue after two precipitations was dissolved in nitric acid and cerium(1V) was reduced with hydrogen peroxide to cerium(II1). Excess peroxide was then hoiled off and the solution was diluted to 1 liter.

Quantities of 40 nig. and above of thorium dioxide were estimated in this way. IVith less than 40 my., half the above quantities of materials were used a n d the total volume of the liquid n-as limited to 100 ml. EFFECT OF pH. Preliminarj- experiments showed that although til-cresoxj-acetic acid did not precipitate the rare earths (trivalent cerium, lanthanum, neodymium, and praseodymium) in acid solution, a turbidity appeared :it pH 3.2. Cerium(1V) is precipitnted even at p H 2.0; hence it is first reduced to cerium (111) with hydrogen peroxide. The effect of acidity on the precipitation and separation of thorium, was studied. The results given in Table I1 show that altering p H from 2.0 to

T a b l e I. S O .

T a b l e 11. So.

pH

1 2 3 4 5 6

3 0 2 3 2 0 1.5

7

TIventy-five milliliters of the solution on precipitation as oxalate and ignition to the oxide gave 0.4330 gram of rare earth oxides exptessed as R20a (after allowing for excess oxygen as estimated from iodine liberated with potawium iodide). Qualitative analysis showed that the residue contained cerium, neodymium, praseodymium, and lanthnnum. I t \vas not further analyzed quantitatively.

E s t i m a t i o n of T h o r i u m

ThOn Taken, Gram 0.0022 0.0083 0,0066 0.0132 0.0221 0 0442 0 0883 0.1327

747

Difference, 11g. +0.2 -0.2 +o. 1 -0.2 +a. 1 +O.l t o 1

.....

EiTert of pII on Precipitation of T h o r i u m Thorium Taken, Gram 0 0883

ThOz I'oiind, Grain 0 0 0 0 0 0 0

1 ,

1.6 1.3

RzOa

1 2 3

ThOz Found. Grail1 0 0024 0 0031 0 0067 0 0130 0 0222 0 0443 0 0886 0 1327

0 0442 0.0888 0 0888

Added, Gram 0.0866 0.8866 1.2990

0885 0886 0883 0880 0875 0870 0808

.%t pH ThOr found. grain 0.0443 0 0906 0 0910

DifferPnre AIg

-0

1

-0

5 0 $5 7

-1

-1 -7 2.3

Diff.. ing.

+O. 1 +2.1 +2.5

At p n 2.0 ThOz found. Diff.. gram mg. 0 0444 0.0902 0 0911

+0.2 f1.7 +2.6

ANALYTICAL CHEMISTRY

748 Table 111. Double Precipitation of Thorium NO.

Tho? Taken, Gram 0.0442 0,0442 0,0885 0,0885 0.0885 0.0885 0.0885 0 0885

Table I\'. ~~~~~l~ so.

Rz0a Added, Gram 0.8660 0.8660 0.8660 0.8660

1.2990 1 ,2990 1.7320 1 7320

ThOz Found, Gram 0.0441 0 0442 0 0885 0 0886 0 0884 0 0885 0 0884 0 0886

Difference, Mg.

-0.1

.....

..... +O.l -0.1 ..... -0.1 +O.l

Analysis of RIonazite

m-Nitrobenzoic Acid Method m-Cresoxyacetic Acid Method Sample, grain ThOn, % Sample, gram ThOr, %

2.5 has no significant effect on the separation. I n all cases the oxide was colored, showing coprecipitation, even a t low percentage of cerite earths. Wash the precipitate of thorium mDOUBLE PRECIPITATION. cresoxyacetate partially (cf. estimation of thorium), and transfer the precipitate and filter to the original beaker. Add 50 ml. of hot 1 to 4 nitric acid, heat on a water bath, and macerate the filter paper to pulp. After the paper has been completely disintegrated (about 20 minutes), cool and filter through a glass filter of medium porosity. K a s h thoroughly with hot water. Collect the filtrate and the washings, evaporate to about 100 nil., and reprecipitate thorium as in the first precipitation. Results of double precipitation are shown in Table 111. Determination of Thorium in Monazite. Weigh about 1 gram of finely ground monazite into a platinum crucible, add 3 to 4 ml. of concentrated sulfuric acid, and heat t o gentle fumes over a microburner for about 3 hours. Add occasionally 3 to 4 drop8 of acid to replenish the acid evaporated. Cool the residue, place the crucible in a 400-ml. beaker, and add quickly 25 ml. of ice-cold water. Stir briskly. Empty the crucible into the beakrr and rinse carefully with ice-cold water. Remove the crucible, let settle, and decant the clear liquid through a Whatman Eo. 42 filter. Stir the residue twice with 5 to 10 ml. of ice-cold water and decant. Ordinarily the residue consists of a few tiny black particles which can be counted; reject the residue. If the residue is appreciable (decomposition of the mineral is incomplete), transfer it to the filter, ignite, redigest, and extract. Combine the two filtrates. rldjust the total volume to 100 ml., then boil. Add 100 ml. of a boiling hot solution of oxalic acid, which has been saturated in the cold, stirring continuously. Set aside overnight. Filter through a Whatman S o . 42 filter and wash with a mixture of equal volumes of 0.2 N oxalic acid and 0.2 M hydrochloric acid until free from phosphate. Transfer the filter and the precipitate to a silica dish and dissolve in concentrated nitric acid. Evaporate on a water bath to dryness. Dissolve the residue in water and repeat precipitation m-ith oxalic acid. Redissolve. .4dd 3 to 4 ml. of 10% hydrogen peroxide and evaporate on a water bath almost to dryness. Cool, stir Kith 15 to 20 ml. of mater, then transfer to a 400-ml. beaker. Dilute to about 100 nil. Determine the thorium on double precipitation.

Murty, Lakshmana, and Raghava ( 5 )recently described the use of tm-o organic reagents-m-nitrobenzoic acid and o-chlorobenzoic acid-where thorium was separated from about 60-fold excess of uranium after a second precipitation. ni-Cresoxyscetic acid appears to be a more valuable reagent in this separation, in that a 100-fold excess of uranium is easily removed. Preliminary experiments indicated that the uranium impurity in the thorium precipitate showed a marked tendency to increase with the time of contact of the mother liquor with the precipitate. A precipitate filtered immediately on precipitation contained but little uranium, whereas the same piwipitate after standing for 24 hours occluded nearly five times as much. Thus in the separation of thorium from uranium, the occlusion of the uranium salt 011 the thorium precipitate appears to he the disturbing factor, rather than the coprecipitation of the element. Experimental. LTranyl nitrate was prepared as follon.li: Pure uranyl acetate, reagent grade, was treated with a slight excess of freshly distilled ammonia saturated with carbon dioxide. The liquid was set aside for 24hours, then saturated with hydrogen sulfide and filtered from any precipitate formed. The filtrate n-a? acidified with dilute hydrochloric acid and boiled to drive off carbon dioxide. From this solution uranium was precipitated with animonia and the precipitate was ignited to the oxide. The oxide was dissolved in pure nitric acid, and evaporated and t,he nitrate was crystallized twice from redistilled water. A stock solution of uranyl nit'rate was prepared from these crystals and standardized by tannic acid ( 1 ) . Ten milliliters of the stock solution gave 0.6060 gram of Ud08. hnimoniuni chloride n-as of analytical grade. In the following experiments suitahle quantities of the thorium and uranium solutions vere mixed to obtain the necessary u r a nium-thorium ratio.

PROCEDURE. To the solution of t'horium-uranium nitrates containing not more than 0.1 gram of the thorium dioxide, add 10 grams of ammonium chloride, followed by 10 ml. of 0.1 S hydrochloric acid, and dilute to 100 nil. Boil and then add 1 gram of ni-cresoxgacetic acid in 100 ml. of boiling water. Continue t o boil for 5 minutes and filter immediately through a 11-cni. Whatman S o . 41 filter. I n this process most' of the precipitate is transferred to the filter. iifter all the mother liquor has drained, wash the precipitate back into the beaker n-ith a hot liquid containing 2 grams of the reagent and 5 grams of ammonium chloride per liter. Stir u p the precipitate three times with 50-111l. portions of the wash liquid in the beaker, let it settle, and pour off the supernatant liquid through the original filter. Now transfer the precipitate completely to the filter, using a policeman to reremove traces sticking to the beaker and complete the n-ashing. Ignite the wet precipitate and weigh as ThOl. I n this way the precipitate is removed from the mother liquor quickly and occlusion. of uranium on the thorium precipitate is reduced to a minimum. The results are shown in Table V. In all except cases 1 and 2 the thorium oxide shows a very slight

Table V. Separation of Thorium from Uranium Expt. SO.

Analysis of Monazite Sand. The sample taken for analysis was from Travancore, South India. Results of analysps with mcresoxyacetic acid are given in Table IV. For compariqon, rewlts obtained with m-nitrobeneoic acid are included.

3

SEPAR4TIOY O F kHORIUM FROM UR4YIUM

7 8 9

The classical procedure employing oxalic acid has been found unsatisfactory by several investigators (5, 7 ) . Ryan, hlcDonnel1, and Beamish (7') successfully separated 10 nig. of thorium from as much as 100 mg. of uranium by precipitating twice n-ith ferron(7iodo-8-hydroxyquinoline-5-sulfonic acid). The further treatment of the ferron precipitate is a complex process. The precipitate is ignited to the oxide and brought into solution by repeated evaDoration of the residue with nitric and hvdrochloric acids. On the whole, ferron is a distinctly superior reagent to oxalic acid.

1 7

4 5 6

10 11

12

ThOz UaOs Tho? Taken, Added, Obtained, Gram Gram Gram SISCXEPRECIPITATIOS 0 I212 0 0646 0 0696 0 0696 0 2424 0 0697 0 0696 0 0696 0 4818 0 7272 0 0698 0 Of396 0 7272 0 0349 0 0348 1 2120 0 0350 0 0348 0 0140 0 0139 0 6060 0 7272 0 0140 0 0139 0 0141 0 0139 0 9696 0 0069 0 0069 0 4848 0 0069 0 6060 0 0070 0 7272 0 0070 0 0069 DOUBLE PRECIPITlTIOS 0 0698 0 0696 0.6060 0 0696 0 4696 0 0696 0 0346 0 7272 0 0348 1 2120 0 0348 0 0348 0 0140 0 ,272 0 0139 0 0139 0 0139 0 9696 0 0068 0 4848 0 0069 0 0068 0 0069 p 7272

Difference, Mg.

.....

fO. 1

.....

t0.2 -0.1 +0.2 +0.1 +0.1 +0.2

..... f0.1 +O.l -0.1

..... -0.2

.....

+0.1

..... -0.1 -0.1

749

V O L U M E 24, NO. 4, A P R I L 1 9 5 2 disoloration, although its weight corresponds to that originally takeg, within limits of experimental error. The thorium dioxide residue in experiments 6 and 9 was dissolved by heating with concentrated nitric acid and a few milliliters of concentrated hydrochloric acid, evaporated to dryness on a water bath with occasional additions of 2 to 3 ml. of nitric acid, and extracted with 30 nil. of water, and the thorium was reprecipitated. Then 20 ml. of the filtrate were made alkaline with carbon dioxide-free ammonia. There was no turbidity nor even a faint color to shoFy the presence of the uranyl ion. Thus the amount of uranium impurity is so small that ordinal- chemical tests fail to show its presence. One can attribute the diwoloration to occlusion of insignificant quantities of uranium. Even when the uranium-thorium ratio wan increased to 100, the discoloration showed no marked increase in intensit.y, nor did the thorium oxide residue show any overweight. I n a second precipitation a pure white residue of thorium dioxide was ohtained.

LITERATURE CITED

(1) Das Gupta. R. RI., J . Indian Cheni. Soc.. 6 , 777 (1929). (2) Gordon. Louis, Tanselow, C . H.. and If-illard, H. H., ANAL. ' CHEW,21, 1323 (1949). (3) Koelsch, C. F., J . A m . Chern. Soc., 53, 304 (1931). (4) Lakshmana Rao, B. R., and Raghava Rao, B. S. V,, J. Indzan Chem. SOC.,27, 457 (1950). (5)

(6) (7) (8) (8) (9)

Llurtv. T. K. S.. Lakshmana Rao. B R.. and Ranhava Rao. B. S.i'., Ihzd., 27, 610 (1950). Xeish, A . C., Ckern. S e w s , 90, 196 (1904). Ryan, D. E.. MoDonnell, IT. J., and Ilearnish, F. E. AYAL. CHEW.,19,416 (1947). Smith, T. O., and James C., J . Am. Chew.Soc., 34,281 (1912). Venkataramaniah. RI.. and Raghava Rao. B. S. V., Analust, 75, I

553 (1950).

(IO) Venkataramaniah, ll.,Satyanarayanamurty, T. K., and Raghava Rao, H. S.V., J. Indian Chem. Soc.. 27, 81 (1950). (11) Willard, H. H.. and Gordon, Louis. ASLL. ( ' H E x . , 20, 165 (1948). R s c b : ~ v t nf u r rerein' AIarch 21, 1930.

.icrel)ted October li, 1931

Determination of Primary Aromatic Amines by Diazotization Using the Dead-Stop End Point H. G. SCHOLTEN' AND K . G. STONE Kedzie Chemical Laboratory. Michigan State College, East Lansing, Mich.

TH"

potle are applicable if availahle. I n any case a galvanometer xith n sensitivity of 0.01 microitmpere per millimeter of scale is d c4rahle. Purification of Amines. All amines determined were purified by recrystallization from a solvent. The first time an adequate amount of Norite was used to adsorti colored materials and a n y impurities that were removable by this treatment. -4s quantitative recovery was no ohject, the ratio of Sorite t,o amine wits Siiigh and ;\hmed (8) proposed the use of a potentiomcJtric end usually 10 t o 25. The substituted benzoic acids and €1acid were recrystallized from mater: 2-naphthylamine and o- and p-nitropoint, but the time factor K:IS not changed. The use of potasanilines were recrystallized from 50% aqueous isopropyl alcohol : qium bromide as a catalyst has been recommended (6,7 ) and is ni-niti,oaniline was recrystallized from 7573 aqueous isopropy! 211niclst helpful for deci,easing the reiiction time. Clippinger and cohol: and isopropyl alcohol alone was used for the nitroamino1'0~1lk( 1 ) h a w suggested that nitrite may be used with cyanide tolucwia. All amines were dried briefly a t 105" and stored over barium oxide until used. f o r the ectablisl~mentof the di.:itl-.stem for the diazotization method l-naphthol-3,6-disulfonic acid, further identification was neces:tromatic amines it iras found th:it the cyanide vas not needed sary t o provide knowledge of the species. T h e sample gave a ir' the potrntial applied betwecri the platinum electrode? \vas 0.4 flanie test for sodium after moistening with hydrochloric acid. ;lectrometric titration of a sample dissolved in tyater n-ith 0.1 S volt. Pn,ler these condition+ i: current flowed R heriever an odium hydroxide showed an acid group nhose pIi was about 3.5 amount of nitrous acid equal to 0.05 ml. of 0.1 -1I sodium nitrite arid another whose p I i was about 8.5. -4s one form of H acid is solution IVM piesent in 200 to 400 nil. of reaction solution. The the monosodium salt with 1.5 moles of water of crystallization, n.r,rk reported here covers t h P use of the dead-stop technique for this form was used for calculating recoveries in the analysis. Independent Determination of Amines. The substituted tlit, tlct~c~rininationof primary aromatic amines and the use of benzoic acids were determined by dissolving samples in water a i d sulfanilic, acid as a stantlard fov sodium nitrite solutions. titrating with 0.1 S sodium hydroxide standardized against potassium acid phthalate t o a phenolphthalein end point. All other EXPERIMESTAL amines except o-nitroaniline were determined b y dissolving in t,he solvent given in Table I and titratiug t o an end point,, using crysApparatus. The electrical circuit and electrodes descrilled by tal violet or methyl violet indicators as descrihed by Seaman and \\-erninioiit itrid Hopkinson ( I I ) are the basic requirements. The .4llen (6)with 0.2 S perchloric acid in glacial acetic acid also S:iI,gent IIoclel I11 manu:iI prrl:irograph and the Fisher Elccdrostandardized against, potassium acid r)hthalate (6). o-Sit,roaniline is so neakly hasic that titration in acetic acid is not possible and no solvent ryas found Table 1. Determination of Pure Amines in ivhich the amine perchlorate was sufB y ;\cidinietry ficiently insoluble to permit the titration .i i i i i ne L C t,r f I S 0 . 0 Salvent Indicat.,r ( h l o r change ', on this basis. Since the method of puri100 2 = 0 2 fication was the same as that which 100 0 f 0 4 100 1 = a 2 100 3 * 0 3 yielded high purity rn- and p-nitroani100 0 * 0 3 100 5 * 0 . 1 line, it n-o;id -seem that the ortho coniBlue to blue-green 99.5 i0.1 100 3 + a 1 2-Saphthylamine pound should also be of high purity. Blue-green toyellow-green 100.5 + 0 . 2 99 9 * 0 2 5-?;1tro-2-aminotoluene 9 9 9 i 0 2 4-Pl'itro-2-aminotoliiene Yellow t o colorless 1 0 0 . 3 zt 0 2 Procedure. Weieh samnlcs which o-Nitroaniline 99.9 r 0 . 1 \vill--drochloric acid (12 S),and 1 3 to 5 determinations. grain of potassium bromide as the c T i t r a n t was 0.1 ,\' XaOH with phenolphthalein indicator. catalyst. Insert the glass paddle of a .i T i t r a n t was 0.2 N HClO+ in HO.4c. e Titrant was 0.1 .V NaOH with electrornetric end point detection. power stirrer and the platinum wire I Crystal violet indicator. electrodes which have been cleaned in Methyl violet indicator.

ckterniination of primnr!. aromatic amines by diazotization (Equat'ion 1) has been troublesome because the detrrtion of t,he end point requir,ed :in external indic,:ttor. usuall?st:trch-iodide paper, and a period of waiting to alloir- the sodium riitrite added to react before teqtiny to see if an excw? was present. R S H J CHI HSO? = RS?C>I 2I1,O (1)

+

+

+

f(jr

~

';

-

i.Calculated

-

as monosodium salt of 8-amino-l-naphthol-3,6-disulionic acid with 1 . j H?O ~

-

1 Present address. Dow Chemical Co.. Bay City. M i c h