wal frequencies. Such a variation in the sc~ondary isotope rate factor in E2 reactions has yet to be testEd experimentally. Between product-like 11 and 13 and reactant-like 12 and 14 must lie estimates of, say, ca. 1.4 a t 100' and ca. 1.3 a t 81' for the chloro and bromo compounds, respc~tively. A negative temperature coefficient in /iN/lin is prodictcd, It is fortuitous that these results check tho :Lvailablc data for tetrabromorthanc.lb Though dctnilcd, these models for E2 reactions are still crude alld only modcratcly succcssful. Further refinement c.lcarly is iiccessary. The reverse processes to 11-14 are halogrn additions for xhich k/k' would be inverse to those given. That is, for debromination, I C I I / ~ D is predicted to be ca. 1.3 and for bromine addition ca. 0.77 at 81'. This agrees generally with the report on the bromine addition to stilbene a t -78' for which liH/lCD = 0.87.24 I n summary, the results in Table I may be re(24) D. B . Denn?y and N. Tunkel, Chem. & Ind. (London), 1383 (1959).
gardcc-l as an cscrcisc in the adjustment of thcoretical models of activated complexes to cxperimental data. Of course, this adjustment generally is possible because the disposable parameters are many. Even so, the linear three-center model failed when the fragnicn t s ircre polyatomic and phould be discarded in these cases. Hou ever, extensive experimental data, the Teller-Rcdli fects, and the temperature coefficient of 1, tend to narrow the choice of a modcl and givr i t some validity. It also is clear that all four terms of (2) mny lie important in assessing k / k ' ; some of these have more often than not hcen ignored. Finally, the use of the results in Table I in making mechanistic distinctions'g* or even in planning a mechanism study, e.g., hydrogen 1's. carbon isotopic substitution, should be evident. Acknowledgment.--We wish to thank Prof. R. 13. Bernstein for several helpful discussions and Dr. IT. G. Lee for doing the calculations on models 13 and 14.
THE ;\SEC€IhSISI11 OF THE EXTRACTTON OF SEVERAL P R O T O S ,ICIDS BY TILT-n-RUTYL PHOSP€ILiTI', BY KEIJIXAITOA X D TOSHIO Sc-zv~r' Japan Atomic Energy Research Iristilute, Tokai, Ibaraki-ken, .Japan Heceiied July 18, 1861
The distribution equilibria of several proton acids (HS03, HCI, HC104, H!IAc, €12S0,, H2C20d, H,P04)bctween aqueoiis and TBP )bases were measured. The mechanism of extraction of these acids mas eonfirmed as a rfiaction betwecn acid ions and T!BP xnolccules, and the formation of the complexes, HNOJ.TBP, 13riO3(TnP)2,.HClSTBP, HCl(TBP),, HClO4(TBP),, HOilc.TBP, and H2C204(TBP)2,was confirmed. The order among the extrsctabihties of these acids suggests that the extractability may be correlated nith the hydration energy of the anion.
Introduction The extraction of mineral acids by THP(tri-n-butyl phosphate) already has been the subjcct of investigations by a few workers. Alcock, ct aZ.,l Peppard, et a1.,2 Tuck,aand Kaito4have made detailed studies of the extraction of nitric acid, and the formation of the complex ISXO3.TBP was confirmed. Yagel, et aLj5 Peppard, et a1.,2 and studied the extraction of hydroRaldwin, et cbhloric, acid by TBP. Recently Hesford, et al.,' have reported new results on the extraction of HCI, "Os, 'fT2S04,HC104, and HF by TBP, and concluded the formation of HCI.TBP, I-IKO,. TRP, H2S04.TBP, and HC104.TBP. KertesS also has made a detailed study on the system of HCl-IS20-TRP, and concluded the formation of the two species: [(TBP)ZWCI(H~O)~] a t lower acid concentration and [TRPHCl(H20)a] at higher acid concentration. (1) K. Alcock, et al., Trans. Paruday Soc., sa, 39 (1956). (2) D. F. Peppard, et ol., J . Inorg. & Xuclear Chem., 8 , 215 (1956). (3) D. G. Tuck, J . Chem. SOC.,2783 (1958). (4) K. Naito, BuU. Chem. SOC.Japan, 8 8 , 363 (1960); 38, 894
(1960). (5) H. A. Pagel, e1 al., Anal. Chem., 81, 1150 (1949). (6) W. 11. Baldwin, et ol., J . Phya. Chem., 68, 118 (1959;. (7) E. Hesford and H. A. C. MrKay, J . Inorg. & Nuclear Chem., 13, I i l l (1960). ( 8 ) A. 9. Kertes, i h d . , 14, 104 (1960).
The present authorsq worked on the THP cxtractions of I-TS03,HC1, IIC104, IIOAc, HzS04, and H3P04independently from the work of Hesford, et al. This paper presents the results of the work iu comparison with those of previous workers. Experimental Reagents.-The TBP was purified by refluving with 0.5% aqueous sodium hydroxide according to the method shown by Alcock, et aZ.1 The other reagents used werc all of A. R. grade. Equipment and Method.-The mewurcments of distribution cquilihrium always were made at constant temperature of 25' using a thermostated water-bath controlled to within f0.1'. The centrifuge tubes containing the sample solution were shaken in the water-bath for about 4 hr. Then, the two phases were separated by a centrifuge. The samples for analysis were taken from each phase. Thr conccntration of acids was determined by titration using an auto-titrator equipped with n glass clcctrode. For the sample.,s of low wid content of HCl, HClO,, or &PO4, the neutron artivation met hod a150 was employed, and the samples were irradiated in the JRR-1 Reactor. In the case of HCI and HClQ samples, the -,-peak height of W 1 a t 1.60 MeV. was compared with that of a standard sample by using the 256-channel pulse height analyzer. In the case of HJPO4 = 1.707 hlev.) was samples, the @activity of **P measured by the gas flow type 2n counter. The calibration curves obtained for both cases showed very good linearity. (9) K. Naito and T. Suzuki, "Tho Mechanism of t h e Extraotion of Several Arid8 by TBP," presented at the Japan Chemical Soriety meeting, Tokyo, April 5 , 1960.
I
1 lo Acid concn. in :q.phase, 01, rnole/l. Pig. 1.-Influence of acid concentration u on the distrihution ratio a t various acid conccntrations, IOOC;/,,230: IIIC204; 6,1JOAc; 0 , HClO4; X, HN03; b, IlJ'O,; A, i k i ; -+, rrci; 0, mo,. __-_-
10 - 2
->_
10-1
.FUP
l r .
. ..
..
. . . . .
.
]pig. 3.--L)ctcrrninution of p in case the salting agent is xbwnt, 25': 0,H2S04( T U P 100%); X, FINO8 (TBP 2W', diluted Lvith (X'L): A. IlCl (TBP 100%): 0 . HClO~(IB1' 20' diluted with bczene). ' - I
4- .- 13.
10-2
.
I
10-1
--e--
I
1 .
1
,
-.-L-
10
Acid concn. in aq. phase, CH,niole/l. Fig. 2.--Influence of acid concentration upon the distribl tion ratio a t various acid concentrations, T B P 2095 (dilute nith CCl,), 25': b , HOAc; 0, H2C904; X , " 0 3 ; 0, HC10, (straight line, diluent, benzene); 0,HClOh (curved line); 0,H#04; A, IIC1; Ij,I ~ J P O ~ . The water content of the T B P phase was determined by Icarl Fischcr titration. Notation.-The notRtion used here is H,X = proton acid ( H + = proton, Xm - = anion) Cn and CX = the equilibrium total concn. in aqueous Dhase of H and X .fA = mean activity coefficient in aqueous phase of the acid H,X an = degree of dissociation of the acid Kd = distribution ratio ( = total concn. in organic phase/ total concn. in aqueous phase)
Results and Discussion Distribution Equilibrium.-The measurement of the distribution ratio, &, of these acids was made
at various acid concentrations. The results obtained are shown in Fig. 1 and 2. ligure 1 shows the results for the case of TBI' used without dilution. In this figure, the dotted line indicates the distribution equilibrium curve of HCI obtained by Pagel, et Q Z . , ~ and it shows that their K,t values are somewhat lower than those of this investigation. The reason for thc discrepancy is not clear, though our data were determined by the neutron activation method and theirs hy titration. The & values of IlCl in the high concentration region, however, arc in good agreement with the rcsults of previous workers. The Kd values for I3NO3, HCI, I-IC104,IlzS04arc in good agreement with those of Hesford, et al., except a fern points in low concentrations of €IC101 and HzSOr. Figure 2 shows thc results for 20% (1-01.) TRP solution diluted with carbon tetrachloride. In the case where the activation analysis was employed, howevrr, benzene mas used instrad of carbon tetrachloride as the diluent, because a trace amount of dissolved carbon tetrachloride may cause some inaccuracy in thc prccisc dctermination of 3 ~ 1 .
The bchavior of thcse acids in distribution equilibrium as shown in Fig. 1 and 2 is to be cxplaincd from the mechanism of extraction of these acids. Analysis of the Mechanism of Extraction.-Thr mechanism of the extraction of nitric acid by T131' has been confirmed as4 II+(aq.)
+ N03-(nq.) + TBP (org.) If
HN08.TBP(org.) (1)
So, it is expected that the mechanism of the extraction of the other acids also is cxplsiiied by the same type of reaction as pH+(aq.)
+ (l/m)pX"'-(aq.) + vTBP(org.)
(IXXddlW')4w&)
(2)
This mechanism can be confirmed by determining the values of p and v as integers without contradiction. The method of analysis has been presented
Jiine, I N 2
EXTR.4CTIOK O F PROTOX h C I I X BY
TRI-n-BUTYL PIIOSPEIATE
--
__
-
. ..
983
-
1 10-1 by this a ~ i t h o rand , ~ the outline of this method is shown in the Appendix. odl (1) Determination of p.-It is convenient to 31 divide thr problem into two cases-strong acids and weak acids. (a) The Case of Strong Acids.-The value 1 of p of eq. 2 is determined as follows. In the g case whrrc there is no salting agent present, 2 the slope obtained by plotting log Kd(H)/f& 2 against log (fkC~l)indicates the value of (1 n / m ) p - 1 as shown in Appendix eq. ii. 2 10-1 ' 10-3" ligure 3 shows the result of this analysis. The I - .. slopcs obtained for HK03, HCl, and HC104 10-8 10-2 10-1 1 indicate that p = 1 for each case. The slope Acid concn. in aqueous pliaw, C'H, mole '1. for I&so4 is about 3 / 2 , and then p is obFig. 4.--Detennination of p i n casr the sdting agent is tained as 5 / 3 . Though it is close to 2, in this added, 25': V, HClO4-NaClO4 ( 5 111): x, HS03-h'nK:()T case, the value of is not an integer. This (1 A I ) ; 6 , HOAc-KOAc (1 &'I; A , HCl-yaCl(4 'If); 0 , H2C204-I
