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V O L U M E 22, NO. 11, N O V E M B E R 1 9 5 0 tatively the components of mixtures of closely related substances, such as members of a homologous series and even isomers. Thus, separations can be effected even if the components exhibit closely related partition ratios. This subject has been excellently reviewed by Craig (4). LITERATURE CITED ( 1 ) Berenblum, I., and Chain, E., Biochem. J . , 32, 295 (1938). (2) Berthelot, JI., and Jungfleisch; J., A n n . chim. phys., 26, 396 (1872). (3) Connick, R. E, and McVey, IT. H., J . Am. Chem. SOC.,71, 3182 (1949). (4) Craig, L. C., A x . 4 ~CHEM., . 21, 85 (1949); 22, 61 (1950). (5) Craig, L. C., J . B i d . Cheni., 155, 519 (1944). (6) Craig, L. C., and Post, O., . ~ N . A L .CHEM.,21, 500 (1949). (7) Debye, P., and Mcdulay, J., Physik. Z . , 26, 22 (1925). (8) Dodson, R., Forney, G., and Swift, E., J . Am. Chem. Soc., 58, 2573 (1936). (9) Edwards, F. C., and Voigt, A. F., ANAL.CHEM.,21, 1204 (1949). (10) Flagg, J. F., "Organic Reagents," New York, Interscience Puhlishers, 1948. (111 Furman. ?;. H.. Mason. W.B.. and Pekola. J. S.. ANAL.CHEM.. 21, 1325 (1949). (12) Furman, K. H., and hlorrison, G. H., manuscript in prepara~I
tion. (13) Garwin, L., and Hixon, A. N., I n d . Eng. Chem., 41, 2303 (1949). (14) Gentry, C. H. R., and Sherrington, L. C., Analyst, 75, 17 (1950). (15) Heberling, J. B., and Furman, X. H., U. S. Atomic Energy Commission, Rept. A-1068 (February 1945). (16) Hecht, F., and Grunwald, A,, Mikrochemie per. Mikrochim. Acta, 30, 279 (1943).
3rd Annual Summer Slympodum
(17) Hixson, A. W.. and Miller, R., U. S. Patent 2,227,833 (Jan. 7, 1941). (18) Huffman, E. H., and geaufait, L. J., J . Am. Chem. Soc., 71, 3179 (1949). (19) Irving, H., Cooke, S. J. H., Woodger, S. C., and Williams, R. J. P., J . Chem. Soc., 1949, 1847. (20) Irving, H., and Williams, R. J. P., Ibid., 1949, 1841. (21) Kirk, P. L., and Danielson, M., ANAL.CHEM.,20, 1122 (1948). (22) Kolthoff, I. M., and Sandell, E. B., J . Am. Chem. Soc., 63, 1906 (1941). (23) .McBryde, W., and Yoe, J. H., ANAL.CHEM.,20, 1094 (1948). (24) Moeller, T., IND. ENG.CHEM.,ANAL.ED.,15, 346 (1943). (25) Moeller, T., and Cohen, A. J., ANAL.CHEM.,22, 686 (1950). (26) Morrison, G. H.. and Taylor, R. P., manuscript in preparation. (27) Nachtrieb, N. H., and Fryxell, R. E., J . Am. Chem. SOC.,70, 3552 (1948). (28) Ibid., 71, 4035 (1949). (29) Nernst. W., 2. phusik Chem., 8, 110 (1891). (30) Palkin, S.,Murray, A. G., and Watkins, H. R., I n d . Eng. Chem., 17.612 11925). (31) Pierlk, C. Ibid., 12, 60 (1920). (32) Rodden, C. J., ANAL.CHEM.,21, 327 (1949). (33) Sato, Y., Barry, G. T., and Craig, L. C., J . B i d . Chem., 170, 501 (1947).' (34) Stolberg, C., 2. angew. Chem., 17, 769 (1904). (35) Templeton, C. C., Rothschild, B., and Hall, N. F., J . Phys. dl. Colloid Chem.. 53. 838 (1949). (36) Warf, J. C., J . Am.'Chem'. SOP.;71, 3257 (1949). (37) West, P. W., and Carlton, J. K., ANAL.CHEW,22, 1072 (1950). (38) Willard, H. H.. and Smith, G. F., J . Am. Chem. SOC.,45, 286 (1923).
k.,
RECEIVED July 8, 1950.
- Separations
THE RARE EARTHS Separative Extraction of Certain Rare Earth Elements as 5,7-Dichloro8-quinolinol Chelates ?'HERALD MOELLER AND DALE E. JACKSON' Noyes Chemical Laboratory, University of Illinois, Urbana, Ill. Although the 8-quinolinol chelates of the tripositive rare earth elements are not quantitatively extracted into chloroform, extraction of the corresponding 5,7dichloro-8-quinolinol chelates is complete in controlled pH ranges. Extraction of neodymium and erbium above pH values of 9.4 and 8.3, respectively, shows extraction to be favored by decreased basicity in the rare earth metal ion. Overlaps in the extraction ranges of these two ions indicate that separations among the rare earth elements through extraction of the 5,7-dichloro-8-quinolinol chelates at controlled pH are only fractional in character. Spectrophotometric studies on chloroform solutions
T
HE tripositive rare earth metal ions show comparatively little tendencies to form complexes with a variety of normally powerful coordinating agents. hlthough this may be due in part to the relatively large sizes of these cations, it is more probable that their peculiar electronic configurations (in general, 4fT5s*5p9render the orbital hybridizations essential to complex formation difficult to achieve. Certain chelating groups, notably the p-diketones and %quinolinols, however, are capable of overcoming this difficulty through the formation of inner complex compounds. Such compounds, in common with inner com1
Del.
Present address, E. I. du Pant de Nernours & Company, Wilmington,
of the neodymium and erbium chelates show broad chelate absorptions centering around 4000 A,, with sharp characteristic rare earth absorptions at longer wave lengths. Bands at 5740, 5818, and 5872 A. for neodymium and at 5208 and 5245 A . for erbium are of particular importance. Neodymium absorption at 5818 A. and erbium absorption at 5208 A. obey Beer's law in the concentration range M and are more intense than corresponding absorptions in aqueous solution. Spectrophotometric determination of neodymium in the presence of neighboring rare earth elements is feasible at lower concentrations than in aqueous solutions.
plexes in general, are difficultly soluble in water but are soluble in a variety of less polar solvents, among them benzene and chloroform. That separations based upon differences in degree of extraction into such nonaqueous media can be effected is thus a possibility. Precipitation of certain of the rare earth elements as 8-quinolinol chelates has been suggested for gravimetric determinations (1, 4, 6, 14, 15). Literature reports notwithstanding, it is exceedingly difficult to form such compounds in the three 8quinolinol to one metal ion stoichiometry predictable from normal valency relations except under very c-refully controlled conditions (3, 5 ) . Instead, basic compounds of widely variable
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Figure 1.
Absorption Spectrum of Chloroform Solution of 5,7-l~ichloro-8-quinolinol Chelate of Neod y mi um
compositions normally result not only with 8-quinoliuol itscxlf (3, 5) but also with such substituted materials as Ekquinolinol5-sulfonic acid (16). I n extraction experiments, however, where an escess of the chelating agent is preseht the material taken into the nonaqueous phase has this 3 to 1 stoichiometry (6). Extraction of 8-quinolinol chelates into chloroform is never complete, but extraction of the 5,7-dichloro-8-quinolinolchelates from aqueous solutions of controlled p H values is easily effected. Inasmuch BS 5,7-dichloro-Squinolinol is a stronger acid than 8quinolinol, ita metal derivatives might be expected to be more ionic and less readily extracted. The apparent anomaly may be due to the reduced solubilities of the chlorinated chelates and their consequent resistance to hydrolysis which would decrease the extent of extraction. Greater ease of extraction of the heavier tripositive ions might be espected because of their reduced basicities (IS). Under comparable conditions, this should be reflected in extraction of these materials at somewhat lower p H values, although since the basicity differences among the rare earth metal ions are not large, large differences in extraction p H values could not be expected. Absorption spectra measurements have been found useful in previous extraction studies involving the Squinolinols (2,7 , IO, 11). The absorption spectra of chloroform solutions of such chelates in general resemble those of the chelating agents except that bathochromic shifts give broad absorptions centering in the vicinity of 4000 A. (9, I f , fa). Because of a general interest m the absorption spectra of the tripositive rare earth metal ions, i t was of interest to determine the effect of chelation upon these
spectra as well. The strong absbrption of the chelating agent iii the ultraviolet limits the choice of rare earth ions to those showing inherent absorption in the visible or near infrared. Furtherinow, the broad chelate absorption around 4000 A. prevents stud,v of ions absorbing in this spectral region from this point of view. Seodymium and erbium ions have sufficient, bands a t longer wave lengths to permit their use. These ions havr the a d d d advantage of differing basicities (IS),thus permitting romp:irativr extraction studies as a function of basicity. Thij p ~ p e i .c m cerns the extraction of these two materials into chloroforni :is 5,7-dichloro-8-quinolinol chelates and with the spectrophotometric characteristics of the resulting nonaqueous solut.ioiis. APPARATUS AND MATERIALS
All absorption spectra measurements were nia
