the calculated values of K , range from (4.8 to 6.1) X lo3. Consequently, a K , of (6.5 f 1) X lo3is indicated, and the conception of the mechanism involved appears to bl: essentially valid. A more refined treatment is not warranted until a reagent of 1 0 0 ~ opurity is available. Attempts were also made to use M T C as a n extractant for ‘Tc(II1) or Tc(1V). Only 2.40/, of the technetium could be extracted from the green colored solution of Tc(II1) which was obtained by coulometric reduction of a Tc(VJ.1) solution, 0.1M in HC1 and 0.5M in KCl, a t -0.03 volt us. S.C.E. Since a polarographic run on the Tc(II1) solution used showel the presence of about 3% of Tc(VII), i t may be concluded that i t is not possible to extract Tc(II1) with the qua1,ernai-y ammonium salt. No significant extraction was found for Tc(1V) ohtained by the reduction of pertechnetate with ascorbic acid. The prior work on perrhenate with M T C (3) indicates the general utility
and great selectivity of this extraction in isolating Re-and therefore also Tcfrom most other elements. Chromium, cobalt, rhenium, and vanadium are among the few elements which might coextract with technetium. Unlike technetium, however, the distribution in some of these systems is strongly pHdependent; hence, resolution from technetium may still be feasible by control of p H in the aqueous phase. Perrhenate can be recovered from the quaternary ammonium salt extract by stripping the latter with 2.5M perchloric acid in three stages (3); over 90% is recovered in the first stripping solution. An attempt was made to separate pertechnetate and perrhenate from 2M HC1 solutions with M T C extraction, which involved measuring the amount of Tc in both aqueous and organic layers by the radiometric method and the unextracted Re in the aqueous layer polarographically. Rhenium follows technetium so closely that their separation from each other is not possible from the indicated medium. This separation
might be feasible, however, using sulfuric or perchloric acid media. ACKNOWLEDGMENT
One of the authors (G.B.S.S.) thanks the National Academy of Sciences (U. S. A.) for an appointment supported by the International Cooperation Administration under the Visiting Research Scientist Program. LITERATURE CITED
(1) Boyd, G. E., Larson, Q.V., J . Phys. Chern. 64, 988 (1960). (2) Moore, Fletcher L., “Liquid-liquid
Extraction with High-Molecular Weight Amines,” NAS-NS 3101, Office of Technical Services, Washington, 1960. (3) Peterson, H. E., MacDuff, J. . S., Hovey, hl. W., Report 5889, [Jnited States Department of Interior, Bureau of Mines, 1961. ( 4 ) Salaria, G. B. S., Rulfs, C. L., Elving, P. J., ANAL.CHEW35, 979 (1!163). (5) Salaria, G. B. S., Rulfs, C. L., Elving, P. J., J. Chem. SOC.2479 (1963). RECEIVED for review February 8, 1963. Accepted AprilJO, 1963.
A Scheme for the Separation of Platinum, Palladium, Rhodium, and Iridium by Solvent Extraction G. H. FAYE and W. It INMAN Mineral Sciences Division, Mines Branch, Deparfmenf o f Mines and Technical Surveys, Ottawa, Canada
b A new scheme is described for the fractionation of solutions containing microgram or milligi*am quantities of platinum, palladiurn, rhodium, and iridium by solvent extraction procedures. The iodide complexes of platinum and palladium are extracted with tributyl phosphote, and thereby separated from rhodium and iridium. Modifications and extensions of existing methods are used for the separation of palladium from platinum and for the separation of iridium from rhodium. The addition of phosphoric acid improves the precision of the stannous chloride-hydrobromic acid method for the spectrophotometric determination of iridilJm. have been developed in these luhoratories for the determination 3f the platinum metals (I1, 12) have involved the use of an anion exchange procedure ( 9 ) for the separation of platinum, palladium, and rhodium in sample ~~olutions obtained subsequent to fire assay. This method is tedious, time consuming, and involves the use of large quantities of perchloric HE METHODS TH4T
and hydrochloric acids; in addition, it does not readily permit the isolation of iridium from a solution of mixed platinum metals. Therefore, an alternative method was sought that would overcome these problems. Various solvent extraction methods for fractionating certain binary mixtures and for separating pairs of the platinum group metals have been proposed (4-6, 16),but, until recently, the literature did not reveal a solvent extraction scheme that will permit the fractionation of a solution containing platinum, palladium, rhodium, and iridium by simple batch-wise operations. After the work described in this paper had been completed, Sen Gupta and Beamish (16) described a solvent extraction scheme in which micro amounts of platinum, palladium, rhodium, and iridium are Separated by a combination of the methods of Yoe and Kirkland (18),and of Tertipis and Beamish (16). The present paper describes an alternative solvent extraction procedure for the isolation of the individual platinum metals from solutions containing microgram or milligram amounts of platinum, palladium, rhodium, and iridium. Plati-
num and palladium are separated simultaneously from rhodium and iridium by extraction of their iodide complexes with tributyl phosphate. Palladium is then separated from platinum with p-nitrosodimethylaniline by the method of Yoe and Kirkland (18), and iridium is separated from rhodium with tributyl phosphate by a modification of the method of Wilson and Jacobs (17). EXPERIMENTAL
Reagents and Solutions. Equilibrated Tri-n-butyl Phosphate (TUP), This was prepared by shaking the purified grade of T B P (Fisher Scientific Co.) with an equal volume of 6 N hydrochloric acid in a separatory funnel for approximately 1 minute. Standard Platinum and Palladium Solutions. These were prepared separately by dissolving an accuratelyweighed quantity of Johnson, Matthey and Co., Inc., Specpiire platinum or palladium sponge in aqua regia, rvaporating the solution to dryness several times with hydrochloric acid, thcn dissolving the residue and diluting to a known volume with 1N hydrochloric acid. VOL 35, NO. 8, JULY 1963
985
Standard Rhodium Solution. This was prepared by dissolving Johnson and Matthey Specpure ammonium chlororhodite in a known volume of 1M hydrochloric acid. The solution was standardized gravimetrically with thiobarbituric acid ( I O ) . Standard Iridium Solution. This was prepared by dissolving Johnson and Matthey Specpure ammonium chloroiridate in a known volume of 1X hydrochloric acid. The solution was standardized gravimetrically with 2-mercaptobenzothiazole (3). More dilute solutions of the above metals were prepared by diluting aliquots of the concentrated solutions t o known volumes with 1N hydrochloric acid. Recommended Procedure. (a) Separation of Platinum and Palladium from Rhodium and Iridium. Evaporate t h e sample solution, containing a mixture of t h e platinum metals as their chloro-complexes, t o incipient dryness in t h e presence of a few milligrams of sodium chloride. Dissolve the salts in 10 ml. of 6iV hydrochloric acid and transfer t h e resulting solution t o a 60-ml. separatorp funnel by washing with a n additional 10-ml. portion of 6 N hydrochloric acid. Shake the sample solution with 5 ml. of an aqueous 4% (w./v.) solution of sodium iodide and allow the mixture to stand for approximately 10 minutes. Extract the platinum and palladium iodide complexes with two separate 15-ml. portions of a 15% solution of T B P in hexane. Withdraw the aqueous phase, wash i t with 10 ml. of hexane in a separate funnel, and then reserve i t for the separation of rhodium and iridium as in Procedure (e). Combine the TBP-hexane evtracts and strip the mixture of platinum and palladium by shaking i t with three separate 10-ml. portions of concentrated nitric acid for approximately 30 seconds each. Place the nitric acid stripping solution in a separatory funnel, dilute with an equal volume of water, and shake with 10 ml. of hexane to wash out as much T B P as possible. If the sample solution is expected to contain 50 pg. or less of palladium, transfer it to a beaker and treat as in Procedure (b) for the separation and/or the determination of palladium. When the sample solution is expected to contain more than 50 pg. of palladium, dilute it to a known volume and remove a suitable aliquot for the separate determination of palladium. I n the latter case, place both the aliquot and the remainder of the solution in separate beakers and treat as in Procedure (b). (b) Separation and Determination of Palladium and Platinum. The following procedure is based largely on thc 11-ork of Yoe and Kirkland ( I @ , but because it differs in certain aspects from their procedure, it is prewntrd in detail hew. Treat the platinum-palladium solution obtained in (a) with a few milligrams of sodium chloride and evaporate to incipient dryness. To convert platinum and palladium to their chloro complexes, add 2 to 3 ml. of 121- hydro986
ANALYTICAL CHEMISTRY
chloric acid, evaporate the solution just to dryness, then repeat these operations twice. ildd 2 ml. of sodium acetatehydrochloric acid buffer solution (14) and approximately 10 ml. of water to the residue in the beaker. Warm the mixture gently for a few minutes and, with a rubber policeman, carefully loosen any sticky salt deposits that may be adhering to the bottom of the beaker. Cool the solution to room temperature in a cold water bath. When palladium is to be determined (in the whole sample solution or aliquot thereof), add 1 ml. of a 0.5% alcoholic solution of p-nitrosodimethylaniline, 15 ml. of 95% ethyl alcohol, and dilute the solution to 50 ml. with water. Measure the absorbance of the solution at 525 mp according to the method of Yoe and Kirkland (I&'), and then determine the palladium content of the sample by reference to a calibration curve prepared from data obtained from standard palladium solutions that have been taken through the T B P extraction procedure. Combine that portion of the solution, taken for spectrophotometric measurements, with the remainder of the solution and transfer the whole to a 60-ml. separatory funnel and reserve for the separation of palladium from platinum. When the sample contains 50 pg. or more of palladium, and an aliquot has been taken from it for the separate determination of palladium, add 2 ml. of the p-nitrosodimethylaniline reagent, 15 ml. of ethyl alcohol, and transfer the mixture to a 60-ml. separatory funnel. Extract the palladium-p-nitrosodimethylaniline complex with two or three separate 10- to 15-ml. portions of chloroform. If milligram amounts of palladium are to be separated, add an additional 1 to 2 ml. of p-nitrosodimethylaniline reagent and continue the extraction with further portions of chloroform until the aqueous phase is light yellow to colorless. Filter the aqueous phase (or aliquot thereof) through a Whatman No. 31 paper into a 400-ml. beaker, add approximately 2 ml. of concentrated sulfuric acid and approximately 5 ml. of concentrated perchloric acid, evaporate the solution to fumes of sulfur trioxide and then cool to room temperature. Boil the sample with 12N hydrochloric acid to convert platinum to the chlorocomplex and then determine the platinum content spectrophotometrically by the method of Ayres and Meyer ( 2 ) or by the procedure of Faye and Inman (11).
(c) The Separation of Iridium from Rhodium. Transfer the rhodium-iridium fraction obtained in (a) to a 250ml. beaker, evaporate nearly to dryness, and treat with a few drops of concentrated nitric acid to destroy iodides. Convert the rhodium and iridium to their chloro-complex by the repeated addition and evaporation of 2- to 3-ml. portions of 12N hydrochloric acid. Take up the final residue of salts with 5 ml. of 6 N hydrochloric acid and wash the resultant solution into a 60-ml. separatory funnel with an additional 5 ml. of 6N hydrochloric acid. Add 5 ml.
of equilibrated T B P and 5 ml. of hexane and shake the funnel and contents for 1 minute. Transfer the lower aqueous phase to a second funnel and repeat the extraction step. Drain the aqueous phase into a clean separatory funnel, a a s h with approximately 10 ml. of hexane, and reserve for the determination of rhodium by the stannous bromide method of Berman and Ironside ( 7 ) . Combine the two TBP-hexane extracts in a separatory funnel and strip the mixture of iridium by shaking it with three separate 1 5 m l . portions of 1:9 hydrobromic acid. The stripping solution is then analvzed for iridium bv Procedure (d). " (d) Determination of Iridium. Transfer the hydrobromic acid stripping solution from (c) to a 250-ml. beaker and evaporate i t to dryness in the presence of a few milligrams of sodium chloride. Add 7 ml. of concentrated hydrobromic acid (which should not be colored), cover the beaker with a watchglass, and boil the solution until i t has evaporated to 2.0 to 2.5 ml. (as judged visually). Transfer the solution to a 25-ml. volumetric flask by washing with 3 ml. of concentrated hydrobromic acid and 7 ml. of 25% (v./v.) phosphoric acid. Place the flask in a boiling water bath and. after 10 minutes, add 5 ml. of stannous chloride reagent as recommended by Berman and McBryde ( 8 ) . Exactly 2 minutes after reagent addition, remove the flask and cool to room temperature in a cold water bath. Dilute the solution to the mark and measure the absorbance of the iridium complex a t 402 mP (8). Determine the iridium content of the sample by reference to a calibration curve prepared from data obtained from standard iridium solutions that have been taken through the entire extraction procedure for the separation of iridium from rhodium. RESULTS A N D DISCUSSION
Extraction of Iodide Complexes of Platinum a n d Palladium with TBP. Yoe and Kirkland (18) developed a method for the simultaneous separation of submilligram quantities of platinum and palladium from other platinum group metals in which the iodide complexes of platinum and palladium are reacted with diethyldithiocarbamate and the resultant products are extracted into chloroform. The present authors considered the possibility that rhodium and iridium do not form iodide complexes readily in a highly acid solution at room temperature, and that the iodide complexes of platinum and palladium [presumably [Pd14]-* ( I S ) and [Pt14]-' ( I ) ] might be amenable to separation from rhodium and iridium by extraction Ivith a suitable solvent. second po.sibility for w c l i a beparation elibts if iridium and rhodium remain as their chloro-complexes and iridium(1T') iy reduced to iridium(II1)
by t8heiodide medium, for i t is known that the chloro-comp:exes of iridium (111)and rhodium are not extracted appreciably by TBP. Experiments performed to determine the feasibility of this itpproach showed that at least 5 mg. of platinum or palladium, as the iodide complex, can be completely extracted from a solution that is 4.7-11 in hydrochloric acid with one 15-ml. portion of 8 . 15% solution of TUP in hexane. I n tach of these experiments, the aqueou:; phase, after extraction, was analyzed by a suitable spectrophotometric method and the platinum met'al under consideration was not detected. Separate experiments with rhodium or iridium showed that, under conditions similar to those above, the extent of estraction of these elements was negligible. Tributj-1 phosphate was chosen for usc in the present investigation because it is capable of extracting the chlorocomplexes of certain platinum metals (5, 17) and therefore v:as considered to be a likely solvent for the iodo-compleses. A 15% solxion of T B P in hexane \vas employed to lower the viscosity of the extractant and thus permit a cleaner separation of the liquid phases. Recovery of Platinum a n d Palladium from T B P Ertract. I n t h e proposed extraction scheme, platinum and palladium had fJo be recovered from t h e organic phase prior t o their separation by t h e steps described i n Procedure (b). For this purpose, mixtures of 12.V hydrochloric acid and 30% hydrogen peroxide, and also nit'ric acid solutions of various concentrations, w r c tested; hoivever, only concentrated nitric acid (about 16N) proved to be satisfactory for the complete stripping of platinum aiid palladium from the ext.ract. Separation a n d Recovery of Iridium. Wilson and Jacobs 117) reported a method for the separ:ition of iridium from rhodium by extmction with tributyl phosphate. These workers were concerned only with the isolation and determination of rhodium, for they discarded the iridium-TI3P extract after t,he separation had been effected and gave no data to show the completeness of the extraction of iridium. T o determine the mtractability of iridium with TBP, experiments mere performed in which various known amounts of iridium sto:k solution were each evaporated to dryness in the presence of a few milligrams of sodium chloride and treated with 3 to 4 ml. of a 1: 1 niisture of 12N hydrochloric acid and 30% hydrogen peroside, to ensure that all the iridium \vas in the quadriv:LIeiit st:Lt,r. Aftw ei.,zporating to dryness and taking u l ~in 6N hydrochloric acid, each sarrlple was taken through the double batJchwise ex-
Table I.
Extractability of Iridium with TBP
Iridium taken, pg. 212
Iridium found, pg. (final raffinate) 8
Extraction, % (difference) 96.7
21 18 33 28 155
.i30 ...
1060 1060 1060 5300
96.0
98.3 96.9 97.4 97.1
Average 97.1
for use in the present work because of it5 comparatively high sensitivity. However, in early tests with standard iridium solutions, this method gave erratic results. Similar difficulty with this procedure has been reported by Tertipir and Beamish (16). Subsequent experiments in this laboratory showed that the addition of phosphoric acid to the iridiumhydrobromic acid system prior to reagent addition, gave highly reproducible results under the conditions described in Procedure (d). A satisfactory esplanation for the stabilizing role of phosphoric acid cannot be given at the present time.
Table 11.
Separation of Platinum, Palladium, Rhodium, and Iridium Taken, pg. Found, pg. ~Palladium Platinum Rhodium Iridium Palladium Platinum Rhodium Iridium
500 50 50 50 50 25_ -
21 309 41 41 41 _21_
21 21 11 214 21 255 -__
21 21 11 21 318 31 --8 _
500 50 52 50 50 24 555 1120 1718
21 319 43 42 40 22 490 1025 1990
23 22 11 210 21 266 .. 511 497 507
19 20 12 21 325 320 515 1044 2125
500 510 530 1060 1000 510 2000 510 2120 When 100 fig. or more of an individual platinum metal was to be determined, diquots were taken from fractions for analysis. 567 1134 1701
traction step with T B P according to Procedure (e). Because of the comparatively large quantities of iridium taken in these tests, the extent of extraction was determined by difference after analyzing the aqueous phase for unextracted iridium by Procedure (d). The results of these experiments are given in Table I. The results given in Table I show that at least 5 mg. of iridium can be estracted from a 6N hydrochloric acid solution with two separate 10-ml. portions of a 1: 1 mixture of T B P and hexane with a n average recovery of 9i%.
In two subsequent experiments with 1060 pg. of iridium, three batch-wise estractions resulted in total recoveries of 99.1 and 99.2%, respectively. Experiments showed that iridium can be readily recovered from the T B P extract by back-extraction with dilute aqueous solutions of hydrobromic, hydrochloric, or perchloric acids. d 1: 9 aqueous solution of hydrobromic acid was chosen as the stripping agent in the proposed scheme of separation and analysis, because iridium is subsequently determined spectrophotometrically in a hydrobromic acid medium by a modification of the method of Berman and 11cRryde ( 8 ) . Determination of Iridium. T h c stannous chloride-hydrobromic acid method of Berman and NcBryde (8) for the determination of iridium was chosen
APPLICATION OF PROPOSED METHOD
A number of synthetic mixtures, each containing various known amounts of platinum, palladium, rhodium, and iridium, mere prepared from the stock solution of the respective platinum metals. Each sample solution was evaporated t o drynes. in the presence of a few milligrams of sodium chloride, treated with a mixture of 12.4' hydrochloric acid and 3091, hydrogen peroxide, and again evaporated to dryness. The residue of salts was then treated according to the Recommended Procedure for the separation and determination of the individual platinum metals. The results obtained in these experiments are given in Table I1 and show that the proposed scheme is suitable for the separation of both microgram and milligram quantities of platinum, palladium, rhodium, and iridium, and also that i t is applicable to mixtures in which the ratio of one platinum metal to others is comparatively high. LITERATURE CITED
(1) hrdagh, E. G. R., Seaborne, F. S., Grant, N. S., Can. Netals 8, 117, 140 (1924). (2) .4yres, G. H., hfeyer, il. S., ANAL. CHEM.23,299 (1951). (3) Barefoot, R. R., SIcDonnell, W. J., Benmish, F. E., Ibid. p. 514. \ - - - - ,
(4) Berg. E. W., Lau. E. Y.. -4naZ. Chim. ' Acta 27, 248 (1962).' (5) Berg, E. W., Senn, W. L., Jr,,, Ibid., 19, 12 (1958). (6) Ibid., p. 109. VOL. 35, NO. 8, JULY 1963
-~
987
( 7 ) Berman, S. S., Ironside, R., Can. J . Chem. 36, 1151 (1958). (8) Berman, S. S., McBryde, W. -4. E. Analyst 81,566 (1956). (9) Berman, S. S., McBryde, W. A. E., Can. J. Chem. 36, 835 (1958). (10) Currah, J. E., McBryde, W. A. E., Cruikshank, A. J., Beamish, F. E., IND. ENQ.CHEM.,ANAL.ED.18, 120 (1946).
(11) Faye, G. H., Inman, W. R., Ibid., 33, 278 (1961). (12) Ibid., 34, 972 (1962). (13) Fraser, J. G., Beamish, F. E., McBryde, W. .4.E., Ibid., 26,495 (1954). (14) Kirkland. J. J.. Yoe. J. H.. Ibid.. ' ~. 1340. ' (15) Sen Gupta, J . G., Beamish, F. E., Ibid., 34, 1761 (1962).
(16) Tertipis, G. G., Beamish, F. E., I b i d . , p . 623. (17) Wilson, R. B., Jacobs, W. D., Ibid., 33, 1650 (1961). (18) Yoe. J. H.. Kirkland. J. J.. Ibid..
RECEIVED for review February 18, 1963. Accepted April 8, 1963.
Behavior of Dialkyl Phosphorodithioic Acids in Liquid Extraction Systems RAQUEL H. ZUCAL' and JOHN A. DEAN Department o f Chemistry, University of Tennessee, Knoxville, Tenn. THOMAS H. HANDLEY Analytical Chemistry Division, Oak Ridge Nafional laboratory, Oak Ridge, Tenn.
b The solubility and acidity of the diethyl, diisopropyl, di-n-butyl, and diisobutyl esters of phosphorodithioic acid in water and the distribution of each between CClc methyl isobutyl ketone, or n-amyl acetate and HCINaCl solutions have been studied. From the data, the acid dissociation constants and the partition coefficients were calculated. No evidence was found for dimerization of dialkyl phosphorodithioic acids in the organic phase. These constants are discussed, together with data for the dialkyl phosphates. The acid dissociation constant i s somewhat larger and the partition coefficient is much larger when comparing di-n-butyl phosphorodithioic acid with di-n-butyl phosphate.
D
phosphorodithioic acids have been screened in acid media for their selectivity in extraction of metal ions ( 7 ) , but little is known about estractants which contain thiono and thiolo phosphorus groups. Hence, the principal objective of this investigation was to establish the general behavior of several individual esters of this class of reagents. The use of liquid-liquid partition to investigate the equilibria of dialkylphosphorodithioic acids in solution seemed most applicable among methods which have been employed to study similar equilibria in view of the strength of these acids and the ultimate employment of the information to metal extraction systems. IALKYL
EXPERIMENTAL
Special Reagents. Dialkyl phosphorodithioic acids. iMethods for preparation and purification have been described, and commercial sources of the reagents listed ( 7 ) . Methyl isobutyl ketone, technical grade, was distilled before use. 988
ANALYTICAL CHEMISTRY
Apparatus. Extractions were performed with a Burrell wrist-action shaker. p H measurements were made with a Beckman Model G p H meter which had been calibrated with a phthalate buffer (pH = 4.01 at 25" C.) and checked against a 0.1N HCl buffer (pH = 1.10) which contained a n appropriate quantity of iYaC1 t o adjust t h e ionic strength. Titrations were performed with microsyringe pipets, 0.5- and 1.0-ml. capacity. Procedure. Equal volumes, 5 ml., of both phases were contacted for a period of 2 hours a t 25" C. Phase separation was assisted by centrifugation at 2000 r.p.m. for 10 minutes. The acid concentration in t h e aqueous phase was determined from a p H measurement or, when [H+] > 0.1M, by a n alkalimetric titration. An extractive two-phase method \vas employed with the organic phase. The concentration of phosphorodithioic acid was determined by an iodometric titration (3, 4). The change in volume due t o mutual solubility or the solvents can be neglected for the system CC'14-water and, although i t is about 5% for methyl isobutyl ketone-water and n-amyl acetate-water, corrections nere not attempted. Reagent Solubility in Aqueous Media. The solubility of di-n-butyl phosphorodithioic acid as a function of HCl or NaCl concentration was obtained by saturating the aqueous phase with the pure reagent during a shaking period of 1 hour a t 30" C. Results are shown in Figure 1. The solubility of the diisobutyl ester was determined also in HCl medium; results superimposed essentially on the curve for the di-n-butyl ester. Dependency of Distribution Ratio on Concentration of Reagent in Organic Phase. T w o methods were suggested by Dyrssen ( 5 ) t o establish whether dimerization of the reagent occurred in the organic phase and, incidentally, to determine the partition coefficient, P, = [HR],/[HR] of the
reagent between the aqueous and organic phases when the acid dissociation constant is known. The subscript o signifies the organic phase. I n one case, the hydrogen ion concentration established by the reagent distributing between a n organic solvent and a n aqueous solution of a univalent salt of a strong acid is plotted as a function of reagent concentration in the organic phase, C,,,. For such a system,
where K, is the dimerization constant of the reagent in the organic phase and K, is the acid dissociation constant in Iyater saturated with the organic solvent. -4 plot of log Cor, us. log [H+][R-] is sho.il-n in Figure 2 for solutions of di-n-butyl phosphorodithioic acid shaken ~ ~ i atnhequal volume of 1-11 SaCl. For each of the organic solvent-water systems the points fell reasonably close to the straight line drawn with a slope equal to one although considerable scatter prevailed. A slope of one implies that the reagent exists only as a monomer in the organic phase and the term involving the dimerization constant may be neglected. Subsequent data will lend further support. I n the second ease, the distribution ratio, D, of the reagent between the particular organic solvent and an aqueous solution of HCl n-as studied as a function of total reagent concentration. For such a system,
+
D = 2 I(* (P,/+)*c, P,/+ nhere d = 1 K a / [ H f ] . On doulile logarithmic coordinates, a plot of D os. the equilibrium concentration of reagent in the aqueous phase, Caq, for a series of fixed HCl concentrations, gives a qe;ies of horizontal lines as shown
+
1 Prcscnt address, Comision Nacional Energia htornica, Bucnos Aires, Argentina.
