ANALYTICAL CHEMISTRY
1204
(5) Reed, J. F.,and Cummings, R. W., IND.ENG.CREM.,ANAL. ED., 12, 489 (1940). (6) Stackelberg, M. v., and Freyhold, H. v., 2. Electrochem., 46, 120 (1940). (7) Stout, P. R., Levy, J., and Williams, L. C., Collection Czechoslov. Chem. Conamuns., 10, 129 (1938). (8) Tsui, C., Am. J . Botany, 35, 172 (1948).
This work was supported by the Atomic Energy Commission Biological and hledical Division] Contract KO.AT (11-1)-159. LITERATURE CITED
(1) Assoc. Offic. Agr. Chemists, "Official Methods of Analysis," 7th
ed., p. 101, 1950. (2) Borcherdt, G. T., Meloche, V.W., and Adkins, H., J. Am. Chem. Soc., 59, 2171 (1937). (3) Kolthoff, I. XI,, and Lingane, J. J., "Polarography," p. 271,
RECEIVEDfor review October 22, 1953. Accepted February 24, 1954. Presented before the Division of Analytical Chemistry a t the 124th hIeeting of the AMERICAN CHEJIIC.ALSOCIETY,Chicago, Ill. Journal Article No. 1562 from the RIichigan Agricultural Experiment Station.
New York, Interscience Publishers, 1946. (4) RIenzel, R. G., and Jackson, 31. L., -4,v.a~. CHEM.,23, 1861
(1951).
Polarographic Determination of Quaternary Phosphonium Salts EUGENE L. COLICHMANI Department o f Chemistry, University o f Portland, Portland,
A
PPLICATIOK of the polarographic method to the determination of aryl and alkylaryl phosphonium salts is indicated by the reduction waves found for two typical quaternary phosphonium iodides. The diffusion current is seen to be proportional to concentration. This study shows that these polarographic reductions can be brought about reversibly a t the dropping mercury electrode. A quaternary ammonium salt, used as a supporting electrolyte, did not interfere with the polarographic determination of the quaternary phosphonium salts, even though the ammonium salt appears to reduce a t a lower voltage. It does not seem likely that this wave is due to impurities] since its height is sizable, and the supporting electrolyte salt used was purified by recrystallizing it twice. Polarographic determinations of quaternary ammonium (8, 10) and sulfonium salts ( I , 4 ) have been reported. These results indicate reductions a t relatively high negative voltages us. S.C.E. Only in special cases, such as those encountered with iodonium salts (6), will these onium polarographic reductions proceed a t voltages low enough that alkali metal supporting electrolyte salts can be tolerated. The present results on quaternary phosphonium salts are no exception. A stability toward polarographic reduction] a t least comparable to the ammonium series, is manifested. EXPERIMENTAL
Polarographic Materials. The apparatus, accessories, and polarographic characteristics were described reviously ( 3 , 6). Determinations were made a t 26.00" f 0.05" C? Drop time was 3.00 seconds. The m value for the capillary was 2.00 mg. per second. m*/at"s = 1.907 mg.*/ssec.-'/Z (open circuit) a t h = 64 cm., where m is the weight of mercury issuing from the capillary per second in milligrams and t is the drop time in seconds. Tetraethylammonium bromide was prepared from Eastman Kodak Co. Khite Label grade triethylamine and ethyl bromide and was recrystallized twice from ethyl alcohol for polarographic use. Maxima Suppressors. The methylcellulose (1500 centipoise viscosity) came from Dow Chemical Co., and the tetradecyltrimethylammonium bromide used was described previously ( 2 ) . Preparation of Phenyltrimethylphosphonium Iodide. Phenyldimethylphosphine was prepared in ether solution by a method similar to that described by Ingold e2 al. ( 7 ) . The following quantities of reactants were employed: phenyldichlorophosphine (0.5 mole) from Victor Chemical Co., methyl iodide (1.5 mole) from Eastman Kodak Cci., White Label grade, and Grignard magnesium turnings (1.5 moles). Contrary to Ingold's method, 1 Present address, Atomic Energy Research Department, North American Aviation, Inc., Box 309,Downey, Calif.
Ore.
it was not necessary to isolate the phenyldimethylphosphine by a painstaking vacuum distillation under anhydrous conditions. Instead, an additional 1 mole of methyl iodide x a s added, and the ethereal mixture was refluxed for several hours. Excess methyl magnesium iodide m-as decomposed with ice water and hydrochloric acid. Then metathesis to the desired phosphonium iodide was completed by heating with a large excess of potassium iodide. The yield of phenyltrimethylphosphonium iodide, which separated from refrigerated aqueous solution, was 81%. The phosphonium iodide obtained was recrystallized from C.P. methanol. The melting point found was 231" C. The melting point was reported to be 236" and 226" to 22'7" C. (6,Q). -4small amount of picrate was prepared for characterization by metathesis with sodium picrate. The melting point found was 133" C. The melting point was reported to be 132" to 133" C. (7). Preparation of Tetra-o-tolylphosphonium Iodide. This symmetrical phosphonium salt was prepared by the same rocedure as Willard ( 1 1 ) describes for the tetraphenyl analog. !'he semisolid] oily phosphonium iodide obtained was washed with several portions of hot water and then extracted several times with alcohol. A portion of the dried residue was fused with sodium. After acidification with nitric acid, an argentometric determination using potassium chromate as an outside indicator showed 24.0% iodide; the theoretical amount is 24.2%. RESULTS AND DISCUSSION
All of the polarographic determinations of the phosphonium iodides were made in 95% alcohol containing either 0.05 or 0.10M
Table I. Polarographic D a t a o n Phosphonium Iodides Concn. of ( E t ) d B r in Alcohol, M
0.05c 0.05d 0.10d
-El,
I,
Volt
U8.
S.C.E.
Id
pa.
Slopea Value
C' Millimolar
Phenyltrimethylphosphonium iodide 2.20-2.22 1.78-1,85 2.30-2.32 1 .so-1.90 2.19-2.20 1.75-1.90 2.32-2.33 1.70-1,87 2.18-2.20 1.73-1.90 2.29-2,31 1.70-1.77
0.055-0.060
0.053-0.060 0.054-0.061 0.056-0.060 0.058-0.060
0.056-0.061
Tetra-0-tolylphosphonium iodide 3.60-3.70 0.025-0.031 0 . 05bs 2.40-2.42 0.05bvd 2,38-2.CO 3,QO-3.95 0 ..026-0.032 O.lOd,* 2,35-2.:I7 3.80-3.90 0.027-0.030 0.10CSf 2.38-2.40 3.76-3.84 0.027-0.0330 a Slope value obtained by plot of E d . s . us. log I/Id I. Concentration range investigated was 0.001 t o 0.003-W phosphonium salt. No maximum suppressor used. d Methylcellulose used as maximum suppressor a t constant ratio (3) of 0 .032570per millimolar concn. of phosphonium salt. 8 Concentration range investigated was 0.001 t o 0.005M phosphonium salt. / Tetradecyltrimethylammonium bromide used a s maximum auppreaaor a t constant ratio (3) of O.bOlM per millimolar concn. of phosphonium salt. 0 Reduction irreversible a t concentrations below 0.002M.
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1205
V O L U M E 2 6 , NO. 7, J U L Y 1 9 5 4 tetraethylammonium bromide (TEAB) as a supporting electrolyte. Methylcellulose and tetradecyltrimethylammonium bromide both proved to be qatisfactory maxima suppressors. Gelatin was not compatible with the systems under investigation. All attempts to xork M ith buffer solutions containing sodium or potassium salts and tetraethylammonium bromide were unsuccessful owing to interference by reduction of the alkali metal ions. I n this respect, tetraethylammonium bromide reduces a t a lower negative voltage than either phosphonium salt. The tetraethylammonium bromide supporting electrolyte showed small reduction waves not proportional to concentration. These came about 0.20 to 0.40 volt before the phosphonium ion reductions. A plateau is obtained between the two onium ion waves, and thus no interference is noted in the reduction properties of phosphonium salts. The polarographic results obtained are given in Table I. Half-wave potential values have been corrected for the small I R drop across the cell. I t is seen that the El82 values do not change significantly with concentration changes in the region investigated. These reduction waves show diffusion current values proportional to concentration within a t least 5%. Slope analysis considerations (Table I ) indicate that the polarographic reduction of phenyltrimethylphosphonium iodide proceeds in two successive reversible 1-electron steps. I n the case of
tetra-o-tolylphosphonium iodide, a slope value equal to approximately 0.03 indicates that the reduction occurs by a single 2-electron reversible process. Rave-height comparison-that is, comparing IdlC values under the same conditions with known ( 5 ) phenyl iodonium salt 1-electron reductions-indicates the same conclusions in regard to the number of electrons involved in these phosphonium ion reduction waves. LITERATURE CITED
(1) Ronner, W.A , , and Kahn, J. E., J . Am. Chem. Soc., 73, 2241 (1951). (2) Colichman, E. L., Ibid., 72, 1834 (1950). (3) Ibid., 74, 722 (1952). (4) Colichman, E. L., and Love, D. L., J . O r g . Chem., 18, 40 (1953). (5) Colichman, E. L., and Naffei, H. P., J . Am. Chem. Soc., 74, 2744 (1952). (6) Fenton, G. W., and Ingold, C. K., J . Chem. SOC.,1929, 2342. (7) Inaold. C. K., Shaw, F. R., and Wilson, I. S.. Itid., 1928, 1280. (8) Pech, J., Collection Czechosloo. Chem. Communs., 6, 126 (1934). (9) Pope, W. J., and Gibson, C. S., J . Chem. Soc., 1912, 735. (10) Van Rysselberghe, P., and NcGee, J. M., J . Am. Chem. Soc., 67, 1039 (1945). (11) Willard, H. H., Perkins, L. R., and Blicke, F. F., Ihid., 70, 737 (1948). RECEIVED for review January 18, 1954. Accepted Bpril 7 , 1954.
Investiga-
tion sponsored by the Research Corp.
Extraction of Niobium into Diisopropyl Ketone From Hydrochloric Acid Solutions H. G. H I C K S and R. S. GILBERT California Research and Development Co., Livermore, Calif.
T
HE extraction of niobium into diisopropyl ketone from mineral acid-hydrofluoric acid aqueous solution has been investigated ( 1 ) . The present work demonstrates the extraction of niobium into diisopropyl ketone from hydrochloric acid solutions in the absence of hydrofluoric acid. A radiochemical separation procedure based on these findings has been designed and found to be excellent. The authors were unable to keep sufficient tantalum in hydrochloric acid solutions, thus rendering cornparison b e h e e n tantalum and niobium unreliable. EXPERIMENTAL
Ten milliliters of concentrated hydrochloric acid were added to about 20 mg. of freshly precipitated niobium oxide containing 35-day niobium-95 and the mixture was digested in a hot water bath. The solution was cooled in an ice bath, saturated with hydrogen chloride gas, and digested hot. This procedure was repeated until the entire precipitate dissolved (usually twice was sufficient) to give a clear, slightly yellow solution which was adjusted to ION in hydrochloric acid. The solution was used as a “stock” solution for the extraction studies described below. A small amount of the stock solution was added to a known volume of standardized hydrochloric acid and the aqueous solution was stirred with an equal volume of diisopropyl ketone for 1 minute in a centrifuge cone. The technical grade diisopropyl ketone had been previously equilibrated with the proper concentration of hydrochloric acid. The layers were then centrifuged and separated, and equal aliquots of each phase were transferred to machined tetrafluoroethylene (Teflon) cups. These cups were covered with pressure-sensitive tape to avoid spilling. The gamma activity of the niobium-95 in the aliquots was counted with a single-channel scintillation pulse analyzer using a thallium-activated sodium iodide crystal. Organic and aqueous phases of the same extraction were counted consecutively in the same position relative to the crystal to minimize errors. The results are shown in Figure 1. 1 Present address, University of California Radiation Laboratory, Livermore, Calif.
In order to check that equilibrium was attained, extractions were performed using mixing times up to 15 minutes. No change was noted in the amount of niobium extracted. No attempt was made to keep ionic strength constant, hence no information was obtained concerning species in solution. DISCUSSION
The data in Figure 1 shovi that niobium extracts well into diisopropyl ketone from 10-11 hydrochloric acid and passes back into the aqueous phase when the diisopropyl ketone is equilibrated with 6M hydrochloric acid. This extraction behavior has been incorporated in the radiochemical separation
a
ag
50
W 0
c W
6: a
0 4
a
IP
HOl MOLARITY
Figure 1. Extraction of Niobium into Diisopropyl Ketone from Hydrochloric Acid Solutions
