Sept., 1958
AGGREGATION OF AMINEEXTRACTANT SPECIESIN BENZENE
forced, of course. It serves only to illustrate that the observed entropies are not inconsistent with independent theoretical estimates, that the permissible vibrational frequencies of physically adsorbed atonis lie between l o l l sec.-l and 1013sec.-1.45r46 More definitive is the minimum in Aswhich occurs at 0 = 0.8. This is unquestionably associated with coinpletioii of the first layer and occupation of the second. An approximate integration of was carried out using the ideal configurational entropy, to extrapolate G t o O = 0. The R In [(l integral entropy so obtained exhibits a minimum very close to 0 = 1. This gives a measure of statistical support4’ t o the B.E.T. value of Nm,on which the coverage values are based. Of considerable interest is the fact that oxygenation of the surface, while eliminating the minimum in (Fig. 3) does not substantially affect the value of Nm (Table 11). This provides a notable demonstration of the empirical consistency of the B.E.T. equation.
as
as,
(47)
T.L. Hill, Advances in Catalusis, 4 , 250 (1952).
1119
Free Energy of Adsorption.-It is of interest that for the adsorption of between 0.2 and 0.5 monolayer of krypton, goes through a minimum as the surface is progressively oxygenated (Fig. 1). It is not possible, therefore, to construct A p for stage I1 for a given krypton coverage in this range by a linear combination of for stage I and that for stage 111. This demonstrates that oxygenation is a continuous process that occurs uniformly over the surface and not in patches. It indicates, furthermore, that the oxygenated layer changes in character as the oxygen coverage approaches that of a monolayer. This tends to confirm earlier proposals on surface r e a r r a ~ i g e m e n tthat ~ ~ ~ were ~~~~ based on the kinetics and heats of oxygenation,l4 the changes in electrical surface properties with progressive o x y g e n a t i o ~ i ,and ~ , ~the ~ thermal restoration of Oxygenated germanium surfaces. lo Acknowledgment.-The author wishes to acknowledge most gratefully the skillful technical assistance of Mr. Charles 8. Martel, Jr.
AGGREGATION OF SOME OF THE AMINE EXTJL4CTANT SPECIES I N BENZENE BY KENNETH A. ALLEN Oak Ridge National Laboratory, Oak Ridge, Tennessee1 Received June 9,1968
In light scattering measurements at 546 mp the normal sulfates of tri-n-octylamine, di-l-i~obuty1-3,5-dirnethyIhexyIamine, methyldi-n-octylamine, 1,3-ethylpentyl-4-ethyloctylamineand di-n-decylamine showed aggregation numbers of 1, 4, 9, 11 and 38, respectively, in benzene solution. Tri-n-octylamine bisulfate is dimeric. The linear dependences on concentration of the 90°/Oo scattering ratios indicated that these solutes were monodisperse. The uranyl sulfate complexes 0% these amine sulfates were all monomeric except that of the primary amine, which a peared t o be a dimer. The monomeric natures of tri-n-octylamine sulfate and of the di-n-decylamine sulfate-uranyl sulgte complex were confirmed by isopiestic and viscosimetric measurements.
Introduction I n previous papers an apparent constant amine sulfate activity in the extraction of sulfuric acid by benzene solutions of tri-n-octyl- and di-n-decyl:imines was interpreted as indicating aggregation of the amine salts.2 Similar evidence for other amines has arisen during the extensive investigations on t,heir use as extractants for u r a n i u n ~ . ~The present light scattering study (supported by isopiestic and viscosimetric measurements) was undertaken in order to establish reliable estimates of the actual particle sizes involved in these systems, with a view toward further elucidation of the associated twophase equilibria. The results of this study have iiot, in general, substantiated the previous interpretation of the apparent activity constancy of these solutes. For example, tri-n-octylamine sul(1) Operated for the U.S.A.E.C. by Union Carbide Nuclear Company. (2) K. A. Allen, THIa JOURNAL,60, 239 (1950); 60, 943 (1956). (3) K. B. Brown, C. F. Coleman, D. J. Crouse and A. D. Ryon, “Progresa Report on Raw Materials,” ORNL-2268, April 26, 1957; K. E. Brown, C. F. Coleman, D. J. Crouae, J. 0. Denis and J. G. Moore, “The Use of Amines as Extractants for Uranium from Acidic Sulfate Liquors-A Preliminary Report,” AECD-4142, M a y 27, 1954; J. G. Moore, K. E. Brown and C. F. Coleman, “Further Studies of the Amines a8 Extractants for Uranium from Acid Sulfate Solutions,” AECD-4145. June 24, 1955.
fate proved to be monomeric, and only one of the other amine sulfates (di-n-decyl) proved to be as large as had been considered reasonable for consistency with the equilibration behavior. Even in this case, one of the important extraction mechanisms based on aggregation has proven untenable (see footnote 10). Further work aimed at resolution of these apparently real discrepancies is in progress and will be described iii future publications. The present paper reports weight average molecular weights for the sulfates and the uranyl sulfate complexes of tri-n-octyl-, di-l-isobutyl-3,5dimethylhexyl-, niethyldi-)t-octyl-, 1,3-ethylpentyl4-ethyloctyl- and di-n-decylamines. Experimental The particular amines studied were chosen on the basis of one or more of such considerations as purity, availability, previous theoretical interest and demonstrated process applicability. Characterizations of the amines, the sulfates and the uranyl sulfate complex forms are shown in Tables I and 11. The compounds were prepared by equilibrating benzene solutions of the amines with aqueous phases containing calculated quantities of sulfuric acid and uranyl sulfate. The pertinent analytical methods have been described e l ~ e w h e r e . ~ ,The ~ apparent monomeric molecular weights shown in Table I1 were computed from (4) K. A. Allen, J . A m . Chem. SOC.,80, 4133 (1958); Anal. Chem. 28, 1144 (1956); A. S. Meyer, Jr., ibid., (in preaa).
K. A. ALLEN
1120
Vol. 62
TABLE I NAMESAND STRUCTURES OF
THE
AMINES
Abbreviation
Amine
Tri-n-octyl
Structure
TOA
Di-l-isobutyl-3,5-diniethylhexyl DBM
H
c-c-c-c-c-c-Lc-c-c-c-c-c
b
b
bI
"-X
MDO
Methyldi-n-octyl
c-c-c--c: 1,3-Ethylpentyl-4-ethyloctyl
b
rc
b
C I
-c-c-cc-h-c-c-c-c-c-c-c-0
Nr A
EPO
c-c-c-c-c-c-c-
-c-c-c-c-c
c: c:
Di-n-decyl
bI
A
H
DDA
c-c-c-c-c-c-c-c-c-c-I&-c-c-c-c-c-c-c-c-c-c t8heweights of amine and water per mole of sulfuric acid for the sulfates, and the weights of amine, acid and water per mole of uranium for the complexes.
TABLE II AMINESOLUTE CHARACTERIZATIONS A.
Amines
Neut. equiv. Found Theor.
TOA DBM
MDO EPO DDA
354 370 270 255 300
35-1, 354 255 255 298
Composition, % Primary Secondary
Teitiaiy
9D 9D 1 07
