where the diffusivity value of dextromethorphanium ion was cm2sec-I which is that assumed to be of the order of 5 X of sucrose. The estimated film thickness in the aqueous layer of approximately 50 microns at the indicated stirring speed appears t o be quite reasonable. It would appear most likely that, on this basis, Equation 9 and similar relationships would be valid to film thickness down t o as low as 5 microns. Thus extractive rates from dispersions of droplets of aqueous phase in a n organic phase of the size of 1 t o 2 mm in diameter would
be expected to be diffusion controlled. Even for partition chromatographic column where the particulates holding the internal phase may be smaller, the general theory may very well still apply. RECEIVEDfor review April 3, 1968. Accepted August 7, 1968. This study was supported in part by grants from Warner-Lambert Pharmaceutical Company, Morristown, N. J., and Smith Kline and French Laboratories, Philadelphia, Pa.
Extraction of Nitric, Hydrochloric, and Perchloric Acids into Carbon Tetrachloride Solutions of Methylenebis[di-n-Hexylphosphine Jerome W. O’Laughlin, Deanna F. Jensen, Jerry W. Ferguson, John J. Richard, and Charles V. Banks Institute,for Atomic Research and Department of Chemistry, Iowa State University, Ames, Iowa 50010 An attempt is made to treat the extraction of nitric, perchloric, and hydrochloric acids from aqueous solutions into carbon tetrachloride solutions of methylenebis[di-n-hexylphosphine oxide], MHDPO, in terms of relatively simple equilibrium expressions. Partition data suggest acidic species in the organic phase of the general stoichiometry n-MHDP0.xH20.yHA. In the case of nitric acid and 0.05M MHDPO the predominant species are those where n = 1, x = 0, and y = 1 or 2; K,(y = 1) = 4.88(M)-2 and = 2) = 0.18 (M)-2. There is also evidence for species where n = 2, x = 1, and y = 1. The latter species appears to be dominant in the case of perchloric acid where kHcIoI = 2.0 x 103(M)p for 0.05M MHDPO. Extensive aggregation was observed in the organic phase at high initial acid concentrations with third phases appearing in the cases of perchloric and hydrochloric acids.
METHYLENEBIS[DI-N-HEXYLPHOSPHINE OXIDE], MHDPO, and related compounds with the general formula, (R)r-P-(CHJ,-P-(R)z
1 0
I
0
have been shown t o be powerful extractants for many metal salts ( I ) . These diphosphoryl compounds, like TBP and TOPO (tri-n-octylphosphine oxide), are usually diluted with some solvents (in the case of MHDPO, carbon tetrachloride, benzene, and 1,2-dichlorobenzene have been used) for liquidliquid extraction studies. Equilibration of a solution of one of these extractants with a n acidic aqueous solution of a metal salt results in the partition of the salt, the acid, and water between the two phases. I n order t o treat the extraction of a metal salt in a quantitative manner it is necessary t o study the partition of water and the acid and t o determine the nature of the water and acid species existing in the organic phase. I n principle, one might hope t o determine a series of equilibrium constants for the formation of the various species involved which would completely characterize the system. I n practice, this is often not feasible, but some useful insights can be obtained from careful studies of relatively simple systems. (1) J. W. O’Laughlin in “Progress in Nuclear Energy,” Series IX,
Vol. 6, D. C. Stewart and H. A. Elion, Eds., Pergamon Press, London, 1966, Chapter 2.
The partition of water into carbon tetrachloride solutions of MHDPO and some related compounds was recently reported ( 2 ) . I n the present paper, the partition of the mineral acids into carbon tetrachloride solutions of MHDPO is reported and a n attempt is made t o treat the data in terms of simple equilibria involving the species believed t o be formed in the organic phase. The extraction of nitric, hydrochloric, and perchloric acids by 1,2-dichlorobenzene solutions of TOPO, MHDPO, and analogous diphosphoryl compounds (n = 2, 3, and 4) was previously reported (3); the data reported were for the extraction of these acids from relatively concentrated acid media, and n o attempt was made t o determine the nature of the acidic species in the organic phase or to calculate equilibrium constants. I n a n earlier paper ( 4 ) the extraction of nitric acid by MHDPO in 1,2-dichlorobenzene was reported and a conditional equilibriumconstant of 15.2 was reported for the extraction of the species MHDPO . H N 0 3from 1Mnitric acid. While the present work was in progress, Goffart and Duyckaerts ( 5 ) reported on the extraction of nitric acid by benzene solutions of MHDPO and analogous diphosphoryl compounds where n = 4 or 5 . They interpreted their data in terms of the stepwise neutralization of the two phosphoryl groups with the formation of the species Y.HNOJ and Y . 2“03 in the organic phase, where Y stands for the extract= 0.35 i ant. They reported Z?, = 10.2 f 0.9 (M)-2 and 0.02 (M)-* for MHDPO. In the present investigation it was found that the latter approach was only of limited usefulness. Extensive aggregation was found in the organic phase in the case of perchloric and hydrochloric acids with third phases appearing when the initial acid concentration was over 1M or 5M, respectively. Third-phase formation was noted in the case of nitric acid only when 0.2M solutions of MHDPO were equilibrated with concentrated nitric acid (over 12714) but vapor pressure lowering
z,
(2) J. W. O’Laughlin, J. J. Richard, J. W. Ferguson, and C. V. Banks, ANAL.CHEM., 40,146 (1968). (3) J. E. Mrochek and C. V. Banks, J. Inorg. Nucl. Chem., 27,
589 (1965). (4) J. E. Mrochek, J. W. O’Laughlin, H. Sakuri, and C. V. Banks, ibid., 25, 955 (1963). ( 5 ) J. Goffart and G. Duyckaerts, Anal. Chim Acta, 39, 57 (1967). VOL. 40, NO. 13, NOVEMBER 1968
1931
Table I. Partition of Nitric Acid and Water into Carbon Tetrachloride Solutions of MHDPO [MHDPO], 0.01
0.01 0.01
0.02 0.02 0.02 0.05 0.05 0.05
0.05 0.05 0.05 0.05
0.05 0.05 0.05
0.05 0.05 0.05 0.05
0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.10
0.10 0.10 0.10 0.10 0.10 0.10 0.10 0.10 0.10 0.10
a
[HN03li
[HNOII, 5 x 10-4 7.5 x 10-3 0.026 9 x 10-4 0.015 0.048 0.00135 0.00176 0.00170 0.0022 0.0049 0.0086 0. 0090 0.0185
0.10 1.0
9.0 0.10 1 .o 9.0 0.0970" 0,0970" 0.1000 0.1000 0.2000 0.2910" 0.2910" 0,4850" 0.4850"
0.0181
0.0182 0.0374 0.0375 0.0378 0,0628 0.0635 0,0805 0.0745 0,0822 0.0792 0.0819 0.0836 0.0859 0.0986 0.101 0.101 0.124
0.5000
0,9540" 1 ,000 1.000 1 . 913a
1.913" 2,863" 2. 863a 2. 863a 2. 863a 3.000 3,820" 3.820" 4. 770a 4. 770a 6.000 9.544 0. 00975 0.0194a 0. 0485a 0. 0500 0,0680" 0.0970" 0.1000
0.1000 0,1940" 0.2000 0.2910" 0.10 0.388@ 0.10 0.48506 0.10 0.500 0.10 1.000 0.10 2,863" 0.10 4.772" 0.10 9.54" 0.20 0.0194" 0.20 0.0680" 0.20 0.1000 0.20 0.1940" 0.20 0.3880" 0.20 0.4850" 0.20 1.OOO 0.20 9.00 These data obtained by
5
x
10-6
8 . 5 x 10-6 7.75 x 10-4 1.38 x 10-3 1.75 x 10-3 2.95 x 10-3 4 . 7 x 10-3 4.40 x 10-3 0.0134 0.0115 0.0204 0.0309 0.0376 0.0377 0.0747 0.1525 0.213 0.234 6.2 x 10-4 5.76 X 8.6 X 0.0263 0.0597 0.0753 0.1430 0.491 potentiometric titration.
[HzOI~ 10-3
