F. R. M. near Garching, and Bernd Bocklitz and the personnel of the reactor station, Garching, for their help with the experimentd work. LITERATURE CITED
(4) Cabell, M. J., At. Energy Res. Estab.
(G.Brit.) C/M-233 (1957).
(5) Gammon, N., Jr., Forbes, R. B., ANAL.CHEM.21, 1391 (1949). (6) Kemp, D. M., Smales, A. A., Anal. Chim. Acta 23, 410 (1960). (7) Meinke, W. W., ANAL.CHEM.31, 792
(1959).
(1) Anderson, S., Wili?y, J. S.,Hendricks, L. J., J. Chem. Physics 32,949 (1960). (2) Banerjee, D. K., Iludke, C. C., Miller, F. D., ANAL.CHEM.33,418 (1961). (3) Baumgktner, F., Kerntechnil 3, 356
(1961).
s., Penniall, R., Ibid., 27, 434 (1955). (9) . , SheDerd. E.. hleinke. W. W.. U. S . At. &.ergy Comrn. AE(U-3879) i1958). (10) Tmka, J., Che7n. Listy 151, 1378 (1957). (8) Natelson,
(11) Tyner, E. H., ANAL. CHEM. 20, 76 (1948). (12) Vickery, R. C.,J . Chem. Soc. 251, (1955). (13) Vpgel, A. I., “A Text-boo& of Quantitative Inorganic Analysis, 2nd ed., p. 827, Longmans, Green and Co. London. 1951. (I4) Naturforsch* 13a, 645 (1958). (15) Young, A , Sweet, T. R., Baker, B. B., A?iaL cHEDI, 27, 356 ( 1 ~ ~ 5 ~ ) . RECEIVEDfor review July 10, 1962. Accepted April 29, 1963. H‘j
’‘
2,3-Diaminonaphthalene as a Reagent for the Determination of Milligram to Submicrogram Amounts of Selenium PETER
F. LOTT,
PETER
CUKOR, GEORGE MORIBER,’ and JOSEPH SOLGA?
St. John’s University, Jamaica 32,
N. Y .
b Selenium is detemnined with 2,3diaminonaphthalene. The reagent permits the determintation of milligram amounts gravimetrically, microgram amounts spectrophcrtometrically, and submicrogram amourits fluorometrically. Masking agents are employed to increase the selectivity so that selenium can b e determined n the presence of tellurium, copper, zinc, aluminum, etc. Data are included on such reaction conditions as the effect of pH, foreign ions on the reaction, and solvent extraction.
T
HE DETERMIXATION of small amounts of selmium is of considerable biological interest since the investigations of Sc hwarz and Foltz (7) which showed t h a t trace amounts of selenium are of nutritional benefit. Kolthoff and Elving (4) recently reviewed methods of selenium analysis. The determination of trace amounts of selenium generally is based either upon a reduction 0 ; splenium(1V) to (.lementa1 selenium 01 a measurement of the piaaselenol form’:d when selenium (IV) reacts with an aromatic o-diamine, particularly 3,3-diaminobenzidene. The use of this reagent has been recently reviewed ( 1 ) . The reagent is not specific; t o preve it the interference of foreign ions, procec ures incorporating masking agents or prior extraction of selenium with toluen1:-3,4-dithiol ( 2 , 8) have been developed. Procedures of
greater sensitivity are desired. Concurrent t o our work, Parker and Harvey ( 5 ) also investigated a series of aromatic o-diamines and similarly observed the greater sensitivity of 2.3diaminonaphthalene (DA4N)as a selenium reagent, but did not apply the reagent to the determination of selenium t o samples containing foreign ions. Gravimetrically, selenium is determined by reduction of selenium(1V) to the elemental state. To prevent the interference of many ions in this procedure, Schumann and Koelling (6) incorporated an ion exchange separation of cations prior t o the reduction of selenium. The use of an organic precipitant for the gravimetric determination of selenium has not been reported. Reported herein is a study on the determination of macro and micro amounts of selenium with DAN, in the presence of foreign ions. The reagent has been found suitable for the direct determination of milligram amount5 of selenium gravimetrically, while micro and submicrogram amounts of selenium are determined spectrophotometrically or fluorometrically, respectively. In addition to the use of masking agents to prevent foreign ion interferences, the separation of macro amounts of forpign cations by ion exchange has been incorporated into the determination of trace quantities of selenium. EXPERIMENTAL
Present address, Brooklyn Technical High School, Brooklyn, N. Y. 2 Present address, Geigg Chemical Co.,
Ardsley, N. Y.
Apparatus a n d Reagents. Optical nieasurements were performed with t h r following instruments: Beckman DU, I’erkin-Elmer Model 202, Bausch
and Lomb Spectronic 20 spectrophotometers, and as Aminco-Bowman Spectrofluorimeter. Aisolution of 2.3-diaminonaphthalene was prepared by dissolving 1.00 gram of 2,3-diaminonaphthalene (Aldrich Chemical Co.. Milwaukee, Wis.) in 1 liter of 0.10N HCI, using a magnetic stirrer . Standard selenium solution containing 5.00 mg. of selenium per ml. was prepared by dissolving 8.168 grams of selenous acid (H2Se03)in 1liter of water. The solution was standardized gravimetrically by precipitation of the selenium with hydroxylamine. Other solutions of selenium were prepared by appropriate dilution of this stock solution. Masking mixture-solution 0.1M in sodium fluoride, sodium oxalate, and EDTA. Procedures. Preliminary experiments indicated t h a t t h e reaction was greatly influenced b y acid concentration, temperature, t h e length of time employed for color development, a n d t h e presence of foreign ions. The conditions cited below should be followed for samples known to contain a diverse number of foreign ions. GRAVIMETRIC PROCEDURE. To a solution adjusted approximately t o p H 2, and containing from 10 t o 50 mg. of selenium, add 25 ml. of the masking agent mixture and 60 to 300 ml. of stock Dd4K solution. (Stoichiometrically, 1 mg. of selenium requires approximately 1 1111. of 0.1% U - i S solution; for complete precipitation a four- to six-fold excess of DdS is necessary.) Adjust the solution to p H 1.5-2.0 by adding either S a O H or HC1, using a p H meter. Allom- the mixture to stand 2l/? t o 3 hours a t room tcmperature. Filter tlie prrcipitate through a fineporo-ity sintered-gla\\ crucible, wash with 20 ml. of l . 5 S HC1 and 50 ml. of water (to remove all traces of HCl), VOL. 35, NO. 9, AUGUST 1963
1159
1.0J
z 4 m c?
0
0.5-
v)
C
m
4 YI
U
0 .O.
200
300
500
400
600
700
800
Z
< m
G?
WAVELENGTH,
2m 4
I
0.0 0
100
I 200
3c 0
T I M E , M I NUTES
Figure 2.
200
300
400
WAVELENGTH,
Figure 1.
500
me
Absorbance spectra
5 mg. DAN in 50 ml. water 100 p g . Se DAN in 50 ml. water DAN 5 0 ml. 50% HCIO4 C. 75 mg. Se D. 100 pg. Se f DAN in 10 ml. toluene E. 5 mg. DAN in 10 ml. toluene
A. B.
+ +
and dry to constant weight a t 110' C. The gravimetric factor for selenium is
selenium, after following the same ion exchange procedure as above, add 0.5 ml. of 0.1M EDTA, 0.5 ml. of 0.1M 0.3385. sodium fluoride solution, and 5 ml. of SPECTROPEOTOMETRIC PROCEDURE. DAN solution, and adjust to p H 2.0. After appropriate treatment to dissolve the sample containing approximately Add 5 ml. of 0.1% DAN solution, 10 pg. of selenium, adjust the solution allow to stand for 2 hours, and extract with exactly 10 ml. of toluene as into p H 2 and pass it through a 2 5 4 . dicated above. Measure the fluoresburet filled to the 10-ml. mark with cence intensity of the sample at an Dowex 50WX8, 50- to 100-mesh reexciting wavelength of 390 mp and a generated resin a t a flow rate of */zml. fluorescent wavelength of 590 mp, per minute. Collect the effluent and using a sample containing 1.0 pg. of any remaining traces of selenium washed selenium as the reference standard. A from the column with 20 ml. of water. linear calibration curve was observed To this solution add 5 ml. of O.l# over the range 0 to 1 pg. of selenium (ethylenedinitrilo)tetraacetic acid diper 10 ml. of toluene. The 0 sample sodium salt (EDTA) solution, 1 ml. of gave a scale reading of 0.10. This 0.1M sodium fluoride and 1 ml. of blank reading, which was reproducible sodium oxalate solution and adjust to within 2%, would correspond to 0.16 p H 1.5-2.5. Add 5 ml. of 0.1% DAN pg. of selenium per 10 ml. of toluene. solution, and allow to stand for 2 hours. Transfer to a separatory funnel, add exactly 5 ml. of toluene, and extract the piazselenol by shaking for minute. RESULTS AND DISCUSSION Separate. To remove droplets of water Properties of the Reagent. Purified the toluene layer is filtered into the DAN exists in the form of white cuvette through a small filter paper plug placed in the stem of the separatory needles. The solid reagent is slowly funnel. The absorbance is determined air-oxidized, forming a yellow-brown a t 380 mp using a reagent blank. The material. An aqueous solution is calibration curves follow Beer's law more readily oxidized but could be over the range 0 to 20 pg. of selenium stored for 3 days under refrigeration per 5 ml. of toluene in a 1-cm. cell a t this without being sufficiently oxidized wavelength. to effect the determination of selenium. FLUOROMETRIC PROCEDURE. To samParker and Harvey (6) reported the ples containing from 0 to 1 pg. of 1160
ANALYTICAL CHEMISTRY
Effect of pH on absorbance
effects of impurities in the reagent on the fluorometric determination of parts per billion concentrations of selenium. Under our conditions we observed no significant difference in the gravimetric and spectrophotometric determination if the commercial or purified reagent was used, as well as in the fluorometric procedure for selenium concentrations of 0 to 1 pg. per 10 ml. of toluene. We performed all work under normal laboratory conditions-i.e., in daylight, not deaerating solutions, or purifying reagents like C.P. toluene. Selenium reacts with DAN to form the piaxselenol which is a reddish colored precipitate. The precipitate is stable to air-drying and will not decompose below 290' C. if carefully washed to remove traces of HCl. Otherwise, the precipitate decomposes a t temperatures below 100' C. Microanalyses of the piazselenol confirmed the formula CloHeNzSe. The piazselenol may be extracted with toluene. Spectral Characteristics. The absorbance curves for DAN and its piazselenol in water and in toluene are shown in Figure 1. The greatest difference in absorption between D A N and the piaxselenol occurs Because the rea t 380 mp. agent has a slight absorption a t this wavelength, a reagent blank should be used in all spectrophotometric measurements. When an equivalent volume of a concentrated mineral acid like perchloric or sulfuric acid is added to an aqueous solution of the piazselenol a bluish colored solution is formed which can be returned to its original color by adding base. This hliic color is probably due to the formation of the diprotonated piazselenol,
Foreign Ion Effect DAN DAN only, gravimetric' Gravimetric' Table 1.
Ion The fluorescent spectrum of the piazselenol shows maxima a t 390 mp and 480 mfi for the incident radiation and a fluorescence maximum at 540 mp. A third fluopescence maximum which was also present in the blank occurred a t 600 mp, which indicates that some 2,3-diamhonaphthalene was extracted by toluene. Therefore, a reagent blank should be run with the analysis, Since the 390/540 peaks were stronger than the 480/540 peaks and the blank readings were comparable in both cases, mertsurements a t the 390/540 peaks were preferred. Effect of pH and Time. Measurements of the absorbance of the aqueous solution of DAN and selenous acid a t various p I I values at room temperature showed t h a t the formation of the piazsel2nol is dependent on the acidity of the solution. As indicated in Figure 2, maximum absorbance occurs :it p H 2 after 100 minutes of standing. T h e color is stable for 4 hours. Heating accelerates the time for reaching maximum absorbance but it also increases the rate of the air oxidation of DAN. Although maximum color coulS be developed by keeping the mixture in a boiling water bath for 10 minutes, this is not recommended because of the instability of DAN. In the giavimetric studies, quantitative precipitation of selenium occurred in 2l/9 to 3 hours a t room temperature. If the mixture was allowed to stand longe-, a t times a white precipitate appeared which may have been the dimer observed by Parker and Harvey (6). Interference Studies. For the spectrophotometric and fluorometric procedure, in t h e presence of masking agents, the primary interference which was observed at a 21300-fold excess of foreign ion t o selenium was due to substances like hypochlorite which oxidized the reagent or reducing agents like Sn(I1) which reduced selenium t o the elemental state (Table I). Using masking agents alone, some ions like zinc, aluminum, or sodium could be present a t a million-fold escess without causing any interference. Copper could not be masked a t a million-fold excess and probably interfenld in the procedure by catalyzing the oxidation of DAN. Incorporating ion exhange separation of macro amounts of cations prevented this interference. Results obtained on analyzing synthetic samples are reported in Table 11. I n the gravimetric procedure, only Ce(IV) and Ti(IV) rmcted with DAN in the presence of masking agents (Table I). Tellurium showed no tend-
+ Masking Agents
Precipitate formation Se(1V) Al(II1) Au( 111) Ba(I1) Bi(II1) Ca(I1) Ce(1V) Cd( 11) Co(I1) Cr(II1) Cu(11) Fe(I1) Fe(II1) Hg(II) K(I) MgW Mn(I1) :?;I)) Pb(I1) Sn(1V) Sr(I1) Te(1V) Ti(IV) UOI(I1) Sb(II1) Zn(I1) Reagents (no selenium) BrEDTA ClO*CN c10,C?O, Citrate P-
Spectrophotometric.
Fluorometricd FluoresAbsorbance cence (%) 0.31 0.31 0.32 0.31 0.31 0.30 0.33 0.30 0.31 0.31 0.33 0.33 0.34 0.28 0.32 0.30 0.32 0.33 0.29 0.31 0.29 0.31 0.37 0.30 0.30 0.22 0.33
89 82 85 89 89 89
0.34 0.26 0.32 0.35 0.34 0.31 0.32 0.34 0.32 0.30 0.54 0.36
88 88 98 91 87 76 97 89 90 80 31
88 88 80
93 88 80 80 88 91 89 93 89 80 82 82 89 89 82 87 89
88 10
88
89 0.30 acid) = 2 ml. of 0.01M ion solution 5 ml. 0.1% DAN eolution at pH 2. b 2 ml. of 0.01M ion solution 2 ml. masking mixture 5 ml. 0.1% DAN; solution at pH 2. 0 Samples contained 10 pg. of selenium masking agents 2 ml. of 0.OliM solution of ion per 50-ml. solution. d Samplea contained 1 pg. of selenium masking agents 1 mg. of 0.01M solution of ion per 50-ml. solution. No observable change.
+
+ + +
+
+ +
ency to react with DAN and some selenium mixtures containing tellurium were analyzed without adding any masking agents. It is necessary t o wash the precipitate with 1.5N HC1 to remove traces of ions, particularly cadmium, which coprecipitate with selenium. The gravimetric results are reported in Table 111. ANALYSIS OF SAMPLES
Copper. Samples of reagent grade copper were analyzed for selenium spectrophotometrically and fluorometrically. For the spectrophotometric procedure, in a 250-ml. beaker add varying amounts (0 t o 10 pg.) of selenium t o 0.5- or 1.0-gram copper samples. Dissolve the copper using 8 ml. of 12M "Os per gram of copper, and after dissolution boil to remove
Table II.
Separation of Cations from Selenium by Ion Exchange
(Selenium taken, 10.0 pg.) Selenium Mixture' found, pg. AI(III), Zn(I1) 10.1 Cu(II), Ca(I1) 10.1 Cd(II), Mn(II), Ni(I1) 10.0 Ca(II), Mg(II), Ba(I1) 10.0 Mn(II), Ni(II), Sr(I1) 10.0 .0.100 gram each ion.
oxides of nitrogen. Add 25 ml. of water and reboil. Adjust t o pII. 1-1.5 with sodium hydroxide. Follow the prescribed spectrophotometric procedure but increase the size of the ion exchange column to that required t o remove all copper from this a m p l e VOL. 35, NO. 9, AUGUST 1963
1161
(a 0.5-gram sample requires 35 ml. of resin) and wash the column with an additional 20 ml. of water. For the fluorometric procedure, add varying amounts of selenium (0 to 2 pg.) to 0.25- or 0.5-gram samples of copper. Dissolve the copper in 5 ml. of 12M "03, after dissolution boil t o remove
Table 111. Masking mixtureja ml.
osideh of nitrogen, add 25 ml. of water, reboil and adjust to pH 1-15 with sodium hydroxide. Follow the prescribed fluorometric procedure, but double the size of the ion exchange column: for 0.5-gram samples wash the ion exchange with three 10-ml. portions of water.
Gravimetric Results
Selenium, mg. Found 24.6, 24.5, 24.9 1 ... 1 ... 49.7, 49.8, 50.3 1 ... 73.9, 74.5 none Te( IV) 24.6, 24.8, 24.8. 24.8, 25.0 5 Te(IV) 24.7 24.8 25 Cd(I1j 24.7 25.0 25 Sb(II1) 24.7 23.7 25 Sn(1V) 24.7 25.2 25 Sb(III), Sn(IV), Th(1V) 24.7 25.1 25 Al(III), Cr(III), Cu(II), 24.7 23.9, 24.2, 24.4, Mg(II), Zn(I1) 24.9 Solution 0.10M in NaF, EDTA, Na2C2O1 All samples were precipitated with fourto six-fold excess of DAN. Foreign ions 25 mg. each
Table IV.
Present 24.7 49.4 74.1 24.7
Results of Selenium Analysis Selenium
Sample Johnson-Matthey' spectrographic copper (0.500-gram sample) Matheson, Coleman & Bella electrolytic foil, Reagent ACS (0.500-gram sample) British Drug Housesa ANALAR Grade copper (0.250-gram samples) Fisher Cert'ifieda copper (0.250-gram sample) J. T. Bakera Reagent Grade copper (0.250gram sample)
J. T. Bake9 Reagent Grade copper (0.500 gram, aa nitrate) J. T. Bake9 Reagent Grade copper (1.000 gram, as sulfate)
Fisher* Certified zinc (1.000-gram sample)
Added, fig. none 0.25 0.50 none 0.25 0.50 none 0.50
1.00 none 0.50
1.00 none 0.50
1.00 none 2.0 5.0 10.0 none 2.0 5.0 none 12.0
24.0
Eimer and Amend* aluminum chloride (1.000-gram sample) Sulfuric acida DuPont Technical (0.200 gram sample) LJrineb
none 12.0 24.0 none 0.5
1.0 none 10.0
20.0
30.0 Fluorometric Procedure. * Spectrophotometric Procedure. 1 162
ANALYTICAL CHEMISTRY
Found, pg. 0.16, 0.16 0.39 0.60 0.46, 0.47
0.71 0.92 0.64, 0.75 1.17 1.64 1.58, 1.78 1.96 2.42 2 79, 2.38 3.26 4.03 4 . 9 , 4.9 7.0 10.0 14.1 7.8, 7.5 8.6 11.0 2.0 1.5.0 27.0 none 13.0 24.0 0.31, 0.32 1.1
1.30, 1.22 none 9.0 22.0 30.0
Av. selenium content, p.p.m. 0.28
0.91 2.7 6.2 11 9.6
6.7 2.6 0.3 1.8
none
Initially samples of copper mere converted to the sulfate after dissolution in nitric acid by adding 3 ml. of concentrated sulfuric acid and heating until copious fumes of sulfur trioxide were evolved. As this gave similar but lower results, due probably to a volatilization of some selenium, this conversion step is not recommended. The copper sample should be dissolved in the minimum amount of nitric acid. If too much nitric acid is employed a poor separation of copper is attained on the ion exchange column. Boiling to remove oxides of nitrogen is recommended to prevent nitrite ion interference. The results of the analvses are listed in Table IV. It is interesting t o note that in the JohnsonMatthey sample, the manufacturer chemically analyzed a 150-gram copper sample and reported that the concentration of selenium in the sample was below his limit of detection of 2 p.p.m. With the fluorometric procedure a 0.5-gram sample was analyzed and found to contain 0.28 p.p.m. of selenium. Zinc or Aluminum. Add varying amounts of selenium t o 1-gram zinc or aluminum samples, and dissolve i n hydrochloric acid. Follow t h e prescribed spectrophotometric procedure; for reagent grade samples if desired t h e ion exchange separation step may be eliminated (Table IV). Technical Grade Sulfuric Acid. Add varying amounts of selenium t o 0.1- or 0.2-gram samples of sulfuric acid, and adjust t o p H 2 with 35% sodium hydroxide. Then follow the recommended fluorometric procedure (Table IV). Urine. Add varying amounts of selenium t o 10 ml. of normal human urine. Xineralize in 100-ml. Kjeldah1 flasks with a mixture of 10 ml. of nitric acid, 4 ml. of perchloric acid and 2 ml. of sulfuric acid. Boil with a Meeker burner; during the course of the digestion the solution turns deep yellow originally and after concentration to about 5 ml., pale yellow. Continue the digestion until copious fumes of perchloric acid are evolved, whereupon the solution again turns colorless, and digestion is stopped. Adjust the solution t o pH 2, with sodium hydroside, boil to remove traces of hypochlorite and follow the recommended spectrophotometric procedure (Table IV). Accuracy a n d Precision. The recovery of known amounts of selenium mas satisfactory from t h e samples listed i n Tables 11, 111, and IV. The gravimetric procedure showed a relative standard deviation of 1.52% while the spectrophotometric and fluorometric procedure showed a relative standard deviation of 9.9% for thc deterinination of selenium in copper. The sensitivity
of the spectrophotometric procedure is 0.0032 pg. per sq. em. for log 10/l = 0.001, and the fluorometric procedure with DAN is over 10 times as sensitive as the spectrophotometric procedure. Although DAN is over twice as sensitive as 3,3-diamin~benzidene it is more susceptible t o interferences. The direct determination of selenium in copper with 3,3-dianiinobenzidene has been reported ( 3 ) . l'his mas not possible with DAN. I n the determination of selenium in biological material bcth reagents were susceptible to some interference which was probably caused by traces of hypochlorite present aftcr perchloric acid
digestion. Experiments are under may t o develop a rapid procedure for the determination of selenium in biological samples. ACKNOWLEDGMENT
The authors express their thanks to K. L. Cheng for his suggestions on this work. LITERATURE CITED
(1) Broad, W. C., Barnard, A. J., Jr., Chemist-Analyst 50, 124 (1961). (2) Cheng, K. L., ANAL.CHEM.28, 1738 (1956). (3) Cheng, K. L., Chemist-Analyst 45, 67 (1956).
( 4 ) Kolthoff I. M., Elying, P. J., Treatise on Analytkal Chemistry, Part 11, Vol.
7, Interscience, Xew York, 1961. (5) Parker, C. A., Harvey, L. G., Analyst 87.558 (19621. (6) Schumann, H., Hoelling, JV.,2. Chenz. 1, 371 (1961). (7) Schwarz, K., Foltz, C. XI., J . Am. Chem. SOC.79, 3292 (1957). ( 8 ) Watkinson, J. H., AXAL.CHEM.32. 981 (1960). RECEIVED for review Sovember 29, 1962. Accepted June 5, 1963. Presented a t the Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy, March 1963. This investigation was supported by research grant GM 09792 from the Sational Institutes of Health, U. S. Public Health Service. One of the authors, G. M., received support through a Sational Science Foundation Fellowship.
Zinc Complexing Properties with Dialkylphosphorodithioic Acids THOMAS H. HANDLEY Analytical Chemistry D,;vision, Oak Ridge National laboratory, Oak Ridge, Tenn.
RAQUEL H. ZUCAL' cind JOHN A. DEAN Department of Chemistry, University o f Tennessee, Knoxville, Tenn.
The composition of the zinc dialkylphosphorodithioate complex which partitions between aqueous acid solutions and CC14 has been established as [(RO)ZPSS]2Zn. Chara zteristic constants have been evaluated; these include the over-all extracticsn constant, the partition coefficient of the zinc complexes, and the stab lity constant of the zinc di-n-butyl and diisobutyl esters. The extractioq mechanism is discussed briefly and the characteristic constants obtained for zinc are compared with those reported for dialkylphosphate complex of zinc.
D
acids have been screened for their extraction of metal ions ( 3 ) from an acid media. and the behavior of several individual esters of dialkylpho*phorodithioic :tcids have been reported ( 8 ) . The manner in w h c h extractablc species form with this class of reagents, and a quantitative evaluation of the extraction characteristics of the zinc complexes were the obje1:t.s of this study. Few pure sulfur chelate complexes have been fully investigated. The dialkylphosphor odithioic acids are known to be quite strong acids (8 and Table I). Among the dialkyl IALKYLPHOSPHORODITHIOIC
1 Present addreos, Co nision Nacional Energia Atomica, Ruenos Aires, ;irgentina.
esters there is only a small change in the acid dissociation constant, but a very large change in the partition coefficients. There is no evidence for association of the reagent in the organic phase (8). EXPERIMENTAL
Dialkylphosphorodithioic Acids. Di-n-butyl phosphorodithioic acid was obtained from Victor Chemical Co., Chicago, Ill. As received, t h e reagent was shown t o be 99.6% pure by electrometric titration. T h e ammonium salt of t h e diethyl ester was obtained from t h e Monsanto Chemical Co., St. Louis, Mo. Other dialkyl esters were obtained from Lubrizol Corp., Cleveland, Ohio. Esters which required purification were converted t o t h e ammonium salts, followed by extraction of impurities with benzene or CC14 and reformation of the acid with addition of mineral acid to the
l a ble 1.
aqueous layer. The free acid may be extracted with CCla and the CCla removed by warming under reduced pressure. The ammonium salts may be recrystallized from ethyl acetate. Because the free phosphorodithioic acids are somewhat sensitive t o hydrolysis, solutions should be prepared fresh each day, or the free acids converted to alkali or ammonium salts. Determination of Metal Distribution Ratio. T h e distribution ratio, D = - -If lo was measured either by use
'
1 M 1'
of radiotracers with carriers (3') or by titrimetric EDTA methods. Except in strongly acidic solutions, the ionic strength was maintained at 1.0. Extractions were performed with a Burrell wrist-action shaker by shaking equal volumes (10 mi.) of the organic and aqueous phases for 10 minutes at 25' & 2' C. in separatory funnels of conventional design. Preliminitry ex-
Characteristic Constants for Zinc Dialkylphosphorodithioates
System: CCL-aqueous acid medium Ester log K* log KcPc lOgP, pKm 10gPc log Kc Diethyl ca. -10 ca. - 9 . 3 0.45 -0.10 ... Di-n-butyl 1.22 6.57 2.52 0.22 2:7t 3.81 Diisobutyl 1.29 5.77 2.63 0.10 2.70" 4.00 Di-sec-butyl 1.37 ... ... ... 2.77" ... Di-( 2-ethy1)hexyl 1.40 ... ... ... 2 86" ... a Estimated from extrapolation parallel to the complete distribution ciirve for di-nbutyl ester on logarithmic coordinates. ~~~
~~~~~~
VOL. 35, NO. 9, AUGUST 1963
~
1163
