Feb. , 1961
SOLVEKT EXTRACTIOX STUDIESOF INTERHALOGEN COMPOUNDS OF ASTATIXE
The isotope distribution among the propanes Ai can be derived from the set dt
= (1
- ~ ) k / ‘ a i -+~ Bk”ai-l
+ k”’ai--2
(D)
B is the fraction of the potentially abstractable hydrogen in the radical which is of the H variety. The first term on the right of (D) arises from the D atom addition to ai-2 with its subsequent participation in a disproportionation reaction in which it abstracts a deuterium from an isopropyl radical. The second term refers to the D atom addition to ai- 1 followed by its abstracting hydrogen from another radical. The third term is associated with reaction (4). The derivation of R from set (B) is simply
5
fj =
( 5 - i)ai
czO--
2 6ai
= .5/fie-k/6
8
Propene with butane as a diluent reacted at 77” The propene mas diluted so that a condition of constant atom concentration through the film could be maintained.4 After reaction, the propene and propane mere separated by gas phase chromatography and each fraction analyzed by mass spectrometry. IC’ was determined from equation (C) with the analytical data for diminution of total propene with time. With the assumption that k = k‘ = k”, the isotopic propene fractions were calculated from the set (B). Although the fractions could not be determined unambiguously from the data of Table I because of lack of reference spectra, the results are in moderately good agreement with the calculated values.6 This is confirmatory evidence that (4)occurs, if a t all, only to a small fraction of (2) under the experimental conditions used in this work. E(. with deuterium atoms.
(E)
TABLE I MASSSPECTRA OF PROPENES FROM THE D REACTION=
2 = 0
Calculation of the A’s gives
d e
etc. 7
A, 2 = 1
This gives k” which is small,
=
aoo[l - e-(k”+ k”311
+ k”’ 5
a, i=o
k’ since, neglecting (3)
=
+
5
Q
A,
325
0
Reaction time, minutes
10
36 1.0 1.0 37 4.8 4.3 38 6.5 6.0 39 28.0 24.8 40 10.8 11.8 41 41.7 36.3 42 25.9 26.1 43 1.0 4.5 0.9 44 45 0.1 46 Relative to the 36 peak.
+ PROPENE
30
100
1.0 3.8 6.0 23.6 12.4 33.0 27.2 8.4 3.3 0.3 0.1
1.0 4.0 6.0 19.3 13.3 27.3 25.3 13.3 7.7 1.7 0.3
= ao0
i = l
If (4)does not occur, then 1;”’ = 0 and k = k‘ = k“.
(6) Data for the propane fractions were also obtained but again lack of reference spectra for the more highly deuterated species precluded a rigidly critical comparison between calculated and observed values.
SOLVENT EXTRACTION STUDIES OF INTERHALOGEN COMPOUNDS OF ASTATINE’ BY EVANH. APPELMAK~ The Department of Chemistrg and the Lawrence Radiation Laboraforg of the UniversitzJ of California, Berkeley, Colifornia Recewed Aueuet 88, 1960
The distribution of astatine between aqueous solutions and CC4 has been used to study the reactions of this synthetic element with 12, I-, IBr, Br- and C1-. The species AtI, AtRr, AtI2,- AtIBr-, AtICI-, AtBrr- and AtCL- have been characterized, and the equilibrium constants interrelating them have been evaluated. These constants have been shown to correlate well with the analogous constants involving the lighter halogens. I n the course of this investigation the equilibrium constant for the distribution of IBr between water and CCl,, and the formation constant of IBrz- have been redetermined, and the results are in substantial agreement with previous work.
Introduction The investigations of the solvent extraction behavior of astatine that have been carried out heretofore have been qualitative in n a t ~ r e . ~ -The ~ (1) Based on work performed under the auspices of the U. S.Atomic Energy Commission. (2) (a) Argonne National Laboratory, Argonne, Illinois. (b) Abstracted from the Ph.D. thesis of the author, University of California (Berkeley), June, -1960 (UCRL-9025).
principal obstacle t o quantitative studies has been the necessity of working with this highly radioactive element only at exceedingly low concentrations. At such concentrations it is difficult to preventthe astatine from reacting with impurities in the experimental system’ (3) G. Johnson, R. Leininger and E. SegrB, J. Chem. Phzls., 17, 1
(1949). (4) H.M. Neumann, J. Inorg. Nucl. Chem., 4,349 (1957). (5) E. H.Appelman, J. Am. Chem. Soc., 82, 000 (1960).
326
1’01. 65 TABLE I I N ASTATINE COMPUTATIONS (21’)
EQUILIBRIUhlCONSTA4NTSUSED KO
Quotient
(I2)ccI&/(
I2 189
86
Salt effecta
+ 0.1[(NaC1) + (NaBr)] + 0.05(NaI)c + 0.03
0.13(NaClO$ (HC104)*
Ref.
9-1 1 d 27.1 9 (1Br)cc1, /( I B r h 4.31 .12(NaC104) O.OSG(NaBr) 0.03(HC104) This work (L-)/(h)(I-) 800 .02(NaX) 0.05(HClOI) 11 d (LBr-)/(L)(Br-) 14.3 12 d !I&l --)/(?Z)(Cl--) -3 12 d (Brs-)/(Br~)(Bx-) 17 13 (IBrZ-)/(IBr)(Br-) 444 .02(NaX) O.O53(HC104) This work [(IBr)2/(Iz)(Br~)1~~la 384’ f 14,15 (I-)(IBr)/(Br-)(L) 2.20 X 10-6 I 9, 14, 15 a Expressed as “A” in the expression log K = log K O A . Stoichiometric salt concentrations are used. Thus, for example, IBr2- is assumed to have the same effect as Br-. “NaX” is sodium perchlorate or any sodium halide. Assumed equal to the effect on the solubility of IZin water.11 c Estimated from the general salting behavior of these ions.lO Assumed to be the same as for the analogous IZand Is- equilibria. e Calculated from the value at 25016 with the heat of dissociation of IBr in CCI, assumed equal to the vapor phase value of 1.36 kcal.’5 1 Assumed to be independent of salt. ( Br2)cC14/(Br2),,1
+
+
+
+
+
We might hope to minimize such troubles by studying the astatine in systems containing macro quantities of lighter halogens, which then ought to react preferentially with impurities that would otherwise react with the astatine. Under such conditions the astatine should usually be present in the form of interhalogen species. Comparison of the characiceristics of these species with those of the homologous compounds formed among the lighter memklers of the halogen family ought to provide considerable insight into the periodic variation of chemieal properties. Experimental
glass vessels a t 21 & 0.5’. Mixtures were agitated continuously until the extraction coefficients became invariant. This condition was usually reached within a minute, but the agitation was generally continued for five to ten minutes. Th- phases were separated by centrifugation. Sodium and hydrogen were the only cations present in solvent extraction mixtures. Mixtures at pH 5 and 7 were buffered with acetate and phosphate, respectively. Otherwise, perchlorate was the only non-reacting anion. Solvent extractions involving astatine were carried out in black-taped vessels. Most of the mixtures were unaffected by light, but some were found to be so photosensitive that the extraction coefficient was altered when the vessel was opened for analysis. These mixtures were worked with in a darkroom illuminated with a Wratten Series 1 Red Safclite (Eastman Kodak Co.). Astatine concentrations ranged from to 10-12 31, and variation of the astatine concentration never had any effect on the extract,ion. Re-extraction of either phase of an astatine extraction mixture with a fresh portion of the other phase generally did not alter the distrihiition coefficient.
Unless otherwise indicated, all reagents were prepared from commercial products of “Analytical Reagent” grade. Distilled water was redistilled from alkaline permanganate for use in these experiments, and Mallinckrodt “low-sulfur’’ carbon tetrachloride was used as the non-aqueous solvent Calculations for all extractions. Sodium perchlorate solutions were prepared by dissolving The equilibria used in calculations are listed in sodium hydroxide in a stoichiometric amount of perchloric acid, and the solutions were analyzed by conversion to the Table I. The astatine extraction result’s are expressed in terms of the distribution coefficient sulfate.6 Sodium halide solutions were analyzed by the Fajans I) = (total At)cc4/(total At)squeous (1) method, using gravimetrically standardized silver nitrate solutions Sodium chloride and bromide solutions were Unless ot.herwise specified, all concent,rations are tested for iodide by oxidation to iodate, followed by boiling in moles per liter, and all species are understood to remove exces,j oxidant, reduction with iodide, and detection of any 1,- with starch.* Bromine was the oxidant used to be in t’he aqueous phase. on the chloride solutions, while the bromide solutions were Results oxidized with excess chlorine in 0.2 M acid. Lower limits The IBr-Br- System.-The equilibrium conof 2 X lofiand 1 X 106 were found, respectively, for Cl-/Iin the NaC1 solutions and Br-/I- in the NaBr solutions. stants and salt dependences of the reactions Fisher Scientific Co. “Purified” IBr was dissolved in CC4, and the solution was tested for an excess of either parent IBr(aq.) = IBr(CC14) (2) halogen by extracting away the IBr with several portions of Br= IBr2(3) IBr 1 M KaBr and examining the residual CCI,. Sufficient iodine was added to react with the slight excess of bromine a t 21’ were needed for the interpretation of astatmine that was found. Halogen solutions were analyzed by addition to excess experiments. This information was obtained from aqueous iodide, followed by titration with a sodium thio- the experiments reported in Table 11. The resultsulfate solution that had been standardized against potas(9) d. Seidell, “Solubilities of Inorganic and Metal Organic Comsium iodate! pounds,” D. Van Nostrand Co., New York, N . Y., 1958, Vol. I. The procedures used for the preparation and analysis of (10) H. S. Harned and B. B. Owen, “The Physical Chemistry of the astatine have been described previously.6 The astatine Electrolytic Solutions,” Reinhold Publ. Corp., New Tork, N. Y., analyses had standard deviations of about 3’35, due princi- 1950, p. 565-566. pally to statisticrtl counting uncertainties. (11) L. I. Katzin and E. Gebert, J. A m . Chem. S o c . , 17, 5814 (1955). Solvent, extractions were carried out in Teflon-stoppered (12) “Gmelins Handbuch der Anorganischen Chemie,” Verlag
+
~______
Chemie, Berlin, 1933, System No. 8, p. 427. (6) W. Hillebrand, G. Lundell, H. Bright and J. Hoffman, “Applied (13) Ref. 12, System No. 7, p. 283-284. Inorganic Analyses,” John Wiley and Sons, Inc., New York, N. Y., (14) D. Yost, T. Anderson and F. Skoog, J . A m . Chem. Soc., 6 5 , 1953, p. 651. 552 (1933). (7) I. Kolthoff and V. Stenger, “Volumetric Analysis,” Interscience (15) Wendell M. Latimer, “The Oxidation States of the Elements,” Publ., New York, El. Y., 1947,Vol. 11, Chapt. VIII. PrenticeHall, Inc., New York, N. Y., 1952. (8) I . Kolthoff and R. Belcher, 1957, ref. 7,Vol. 111, Chapt. VI-VII. (16) J. H. Faull, Jr., J . A m . Chem. Soc., 66, 522 (1934).
SOLVES’r EXTR \CTIO?;
Feh., 1961
327
STUDIES O F I S T E R H ~ i L O G E SCOMPOCSDS O F A k T I T I S E
ing constants, from which the “Dca,cdl’were computed, are
+ 0.12(KaClO4) + 0 096(SaBr) + 0.03(4) log K3 = log 444 + 0.02(NaX) + 0.053(HC104) ( 5 )
log K 2 == log 4.31
(HClO,)
where “NaX” is XaCIOk or NaBr. Due to the limited data, the salt dependences are not unique, but were assigned by analogy with the corresponding dependences shown by the Izand 13equilibria. Their subsequent use in this paper cannot introduce any great error.
\
TABLE I1 DISTRIBUTION OF IBr BETWEEX CCla A N D AQUEOUS BROMIDE
SOLUTIO^
10-2
Titer (an IBr)
n 1 2 4 4
13Gb 02gC 50 48 4 5Zd 4 4Se 47 3
AqueFree -D-HClOd ZNaBr ous CCli BrExptl. Calcd. 102 x 103 103 103 x 1 0 2 x 102 x 1 0 2 0 905 318 318 100 1 438 15 91 1 822 73 7 73 4 99 12 18 3 318 1 930 10 58 95 5 9 66 9 68 89 110 0 1 579 14 84 95 2 10 1b 10 14 6 0 109 4 1 622 14 49 96 2 10 70 10 71 ii 0 110 3 1 691 14 39 96 0 12 08 12 05 6 0 109 1 1 829 13 74 6 5 960 2 051 134 4 826 1 385 1 384
x
x
+
i1
\ j
L
I
x
aR = organic volume/aqueous volume. D = (IBr)ccl,/ (IBrz-)]. In the calculation of the D‘s, cor[(IBr)aq. rection has been made for the generation of 1 2 and Br2 in each phase by dissociation of IBr, and for the forination of 12Br- and Bra-. ZSaBr is the stoichiometric concentration added to the mixtures. Free Br- = BNaBr - IBr2-. Unless otherwise indicated, the stoichiometric concentrations of IRr and 12,expressed as if all the halogen remained in the CCl?, are (ZII~)CCI~ = t X and (ZIBr)cci4 = 4.88 x 10-3. High acid and (-cess 1 2 are present in the experiments at low bromide concentrations to repress the (Z12)ccla = 0.01058 and (ZIBr)ccl, hvdrolysis of the IBr. = 6.94 X 10-3. ( Z 1 2 ) ~ ~= 1 41.953 X 10-3 and (ZIBr)cc14 = 2.40 X 10-3. d T h e aqueous phase was 0.28 M in KaC104. e The aqueous phase was 0.785 A f in NaC104.
z
t
-1
1 c
-- -,
>___.-J
-
-LLJLL-_-LL---l
1
3
1 -
11-1.
Fig. 1.-Distribution of astatine between aqueous iodide solutions and iodine-containing CC4: 0, 5-10 X lo-* M (12)cc14, pH 3.0 (other experiments deviate from these conditions only as indicated); A, 0.8-1.OM NaC104; 0, pH 1.1 and pH 4.6 (identical results from two experiments); U, pH 6.9; A, 0.08 M (1a)ccip; 0, 2-3 X M (Iz)cci4.
50% above the calculated curve of Fig. 1, and usually decreased slowly over several hours. The cause of this behavior was never determined, but the difficulty was eliminated by preparing new reagent solutions, suggesting that an unknown impurity mas at fault. In mixtures with high iodide concentrations, D sometimes dropped as much as 15% when the aqueous phase was re-extracted with a fresh organic phase. Further re-extraction did not alter D. Astatine in the &-I- System,-In this system This drop may be due t o the extraction of small the distribution of astatine is independent of the quantities of compounds of astatine with imiodine concentration between 10-1 and 2 X 111 purities. Assuming this to be the case, we have (Iz)cCll. The distribution coefficient is independent taken the final value of D to be the correct one. of acidity between pH 1 and 5, but drops about 25% Astatine in the Iz-IBr-Br- System.-These reat pH 7, when the iodide concentration is M . sults appear in Table 111. The distribution of the The iodide dependence of the distribution is astatine is seen for the most part to be a function illustrated in Fig. 1. The smooth curve has been of only the Br- concentration and the ratio IBr/12. calculated from the equation ilt a given Br- concentration, D decreases with increasing IBr/Iz, leveling off a t high values of the D = K;/[l + Ks(I-)I (6) ratio. Increasing Br- decreases D a t any value of with the assumption of the equilibria IBr/12. This suggests the reactions KT = (.ltI)ccld/(AtI)sq Kg = (.\t12-)/(AtI)(I--)
=
=
5.5 2000
(7)
(8)
The dependence of the distribution on inert salt may he represented approximately as log D = log Do + O.l(SnClO4) (9) The sodium iodide itself would be expected to have a much smaller effect.1° From the lack of pH dependence we may set an upper limit of to the equilibrium constant for the hydrolysis reaction H20
+ it1
=
HOAt
+ H’ + I-
(10)
The lack of Iz dependence rules out any oxidation-reduction reaction, and also excludes the reaction of At1 with iodine to give At13. I n a series of early experiments with this system, the initial values of D were sometimes as much as
+ + +
+
At1 IBr 5 &4tBr 1% A t 1 Br- = AtIBrAtBr Br- = -4tB1-2-
(11) (12) (13)
The calculated D values of Table 111 have therefore been computed from the expression in which the aqueous IBr/I2 ratios are twenty times the tabulated CC1, values. KII, Klz and Klr have been set at 190, 120 and 320, respectively, and K15 =
(AtBr)ccl,/(AtBr),,
=
0.040
(15)
Since most, of the mixtures have high salt concentrations, the effect of the medium on these equilibrium must be considered. The most important effect is probabiy that of sodium salts on
328
Vol. G5 L)ISTRIBUTIONOF
R
-Aqueous-ZNaBr 103
x
Brloa
x
TABLE I11 ASTATINE IN THE 12-IBr-Br- SYSTEM'
212 x 104
Br-
--CClr XIBr
-
x
104
D--.-.. IBr/Iz
Exptl.
Calcd.
102
102
102,
x
x
x
9 X 10-4 3f 0.94 1.89 0.93 220 960 0.374 0.034 240 .94 1.89 .91 37 9GO 3.74 0.34 33 .94 2.07 .92 87 1.71 1.73 9.7 10 1.08 1.96 .93 11 10 1.71 930 18.2 0.94 1.89 3.4 .93 5.6 6.6 9.5 0.374 1. e 4 4.5 .01 1.86 4.9 980 96 8.5 1.G4 4.5 1.8,6"C .86 4.9 8.4 980 96 2-4 0.94 3.4 0.91 .91 8.0 3.90 37 0.94 3.B .93 3.2 0.94 0.73 1.50 160 1.08 3.2 1.9:3 * 93 9.5 18.5 170 3.5 1.63 2.02 2.7 3.1 .97 1.09 88 1700 2.02h.C 1.63 3.1 I92 1.09 88 1700 2.5 Rr0 X 10-8 211 120 0.91 9.1 9 .o 0.021 110 1000 0.364 53 .90 9.0 8.8 60 1000 1.38 .065 20 .9L 9.1 9.1 18 100 0.426 .20 .9.L 8.8 20 9.1 .20 1000 4.30 17 21 9.3 .93" 9.0 .171 980 3.72 17 .g'p." 9 0 .22 17 15 8.7 960 4.68 9.2 .9:7a .24 17 16 8.9 930 4.56 .88 8.9 7-9d 8.0 8.3 .61 990 12.7 2.2 .93 9.1 9.7 0.460 2.9 2.8 9.1 .93 10.8 2.1 3.1 2.9 9.1 860 38.2 .90 16.7 9.0 1.6 700 195 13 1.3 1.2 22 .9:1 10.8 9.2 1.3 81 38.8 9.1 9.1 1.2 .9:: 27 0.81 0.460 0.95 9.2 1.2 29 9 .o 7.6 4.74 1.2 .03 .91." 100 1.o 1.o 9.4 0.54 1.26 9.3 .92 1.o 9.4 220 0.79 9.4 0.30 1.46 23.4 .91. 8.G 1.1 180 1.2 105 390 10.1 .9:: 1.o 0.402 19.0 1300 9.3 1.o .91. 23 . 4 1.1 1600 0.39 8.7 4.29 393 Rr0.09 M 1.8s 94 93 0.0168 16 19 980 0.356 94 92 .069 0.7 1.86 980 3.72 5.5 94 0.90 0.74 1.8G .65 94 9.6 0.356 1.84 101 94 .63 990 48.5 .84 .73 .24 94 .20 7.9 93 1.8G 8.1 3.72 160 .19 .31 9.4 89 2 . OOf 910 44B 119 .12 .13 3.16 12.7 0.9Eif 118 33 121 121 .11 .11 0.243 1.54 0.92f 49 102 .20 102 .13 0.585 4.86 0.90f 73 103 .22 96 81 1.81: 10.0 48.5 .13 101 .10 93 1.21 96 0.91f 670 .13 110 2. OOJ 680 184 .14 .ll 9.3 446 Br0.9 M e 940 930 1.86 0.0206 1.8 980 3.80 2.0 940 920 1.86 ,099 DGO 38.2 0.57 0.57 940 940 1.87 .34 .173 .34 9.7 0.356 1.17 940 1 .Si 940 7.9 3.80 .1G .0b4 1000 1.28 1.95' 900 , 1 1 4 ,lSd 910 446 .063 11.5 930 920 10.0 48.5 .019 1.82 .13 1.94 900 340 1.27 172 870 .0260 .015 460 2.04 960 0.99 172 .11 ,014 920 920 460 960 .014 2.04h .10 0.99 172 The L)'s are defined by equation 1. The other symbols are those defined in note ( a ) to Table 11. To obtain (I%/ Iz)cc14from the raw data it was necessary to correct for the distribution of the halogens between the phases, for the formation of IzBr- and IBi-t-, for the dissociation of IRr, and for reaction 16. Unless otherwise specified, HC104 = 0.063 M and No NaC104 was resent. d The results of duplicate experimente scah WaClO, = 0.40 .- XNaBr. * HC104 = 1.02 M . tered over this range. 8 HCI04 = 0.03 M . f NaClO, = 0.48 - ZJaBr. 0 Re-extraction of the aqueous phase with two successive portions of pure CC4 gave succes9ive D's of 1.8 and 1.3 X lo-*. I-ICIO, = 0.0063 M . 2
-
-
-
0
Feb., 1961
SOLVENT
EXTRACTION STUDIES O F IXTERHALOGEN COMPOUNDS O F ASTATISE
K?, which is reflected in equation 9. Accordingly, in the use of equation 14, K , has been corrected for salt concentration by means of equation 9, in which D and Do are replaced by K7 and K7’. We have further assumed all sodium salts to have the same effect. Other salt effects should be considerably less important, and this is the only correction that has been made. This procedure appears justified by the observed effect of acid and inert salt on the astatine distribution in these systems. We may note that the distribution is independent of acid concentration between 0.006 and 1 M . Most of the mixtures with high IBr/12 ratios were found to be photosensitive, exposure to light causing a several-fold increase in D. We see that the astatine becomes less extractable than predicted at very high IBr and low Ipconcentrations. This may indicate oxidation of the AtBr to the higher positive state to which bromine is known to oxidize astatine.3~~On the other hand, at high bromide concentrations, when “DCalcd’) is less than the observed D is generally severalfold greater. This may result from the extraction of impurity compounds suggested in the preceding section, an effect which would now become much more prominent due to the very low values of the “true” distribution coefficients. In this case a drop in D might be expected upon successive reextraction of an aqueous phase with fresh organic phases, and such drops were sometimes observed. Astatine in the 12-I--Br- System.-This system links the two preceding ones, and the results obtained in it appear in Table IV. Although no IBr has been added to these mixtures, the interhalogen is generated by the reaction 12
+ Br-
=
IBr
+ I-
(16)
Although equilibrium in this reaction lies to the left ( K = 2.2 X the ratio IBr/12 can reach significant values at low iodide and high bromide concentrations. Values of “ D o a l C d ” have therefore been computed from equation 14 as in the previous section, with the addition of the term “&(I-)” in the denominator to account for formation of AtL-. We note that when the iodide concentration is varied at constant bromide concentration, a maximum in D is predicted, since D is reduced a t low iodide by the formation of AtBr and at high iodide by the formation of At12-. These experiments showed about the same salt effects as those of the preceding section, and the distribution was independent of acid concentration between lov3and 6 X M. Although the data in Table IV generally follow the trend of the calculated D’s, the observed D’s decrease much too sharply at high IBr/12, suggesting that some further unknown reaction is coming into play. Also disturbing is the fact that in some of the systems D drops markedly upon re-extraction of the aqueous phase. Astatine in the I,-I--CISystem.-Table V gives the results in this system, which is the chloride analog of the 12-I--Br- one. I n this case, however, instead of introducing the IC1-producing reaction analogous to equation 16, we shall write the astatine reactions
329
TABLE IV DISTRIBUTIONOF ASTATINE ----Aqueous-
Br 102
1-
x
THE
Iz-I--Br-
x
SYSTEBI~
D -
IBr/Iz
ZIP 104
x
x
10‘
IN
-CCL-
Exptl.
x
106
102
Calcd. x 102
Br0.01 M 1.01 10.0 0.26 1.01 10.0 1.06 0.89 19.6 5.1 1.02 10.0 29 0.88 1000 85
48 130 250 200 180
52 130 240 200 180
10.0
110
150
N
42.0 10.5 1.92’lC 0.387 .114b~”-d ( ,0470) .I30
1.03
87
Br0 . 1 Illr 10.0 1.06 10.0 10.5 9.8 44 9.8 44 1O.U 87 0.81 820 N
102 10.5 2. 23b 2.32’ 1.27 0.138 ( ,130) .116”-“f ( ,0243) .116e*.f ( .0243)
9.8 10.1 9.0
9.3 10.1 10.3
19 38 31 27 16 2.6
17 34 36 32 23 4.8
9.3
10.0
880
3.1
5.3
9.3
10.0
880
3.1
5.3
Br- N 1 M 6.8 4.9 8.8 109 87 9.1 3.0 4.49 9.6 90 9.4 103 2.2 2.4 152 6.7O 92 1000 (0.0245) 2. 8OC 91 19.6 360 1.3 1.3 (2.36) 0.91c 93 10.1 1110 0.42h 0.51 ( .097) .91 93 10.1 1110 0.40’ 0.51 ( ,097)’ 0 The symbols are explained in note ( a ) to Table 111. The bromide concentration has been corrected for the small amount tied up as 12Br-. The iodide concentration has been corrected for 11- formation and for the iodide produced by reaction 16. When the correction exceeds 270,. the stoichiometric concentration of added sodium iodide is indicated in parentheses in the I- column. The IBr is produced by reaction 16 and has been calculated accordingly. Unless otherwise indicated, the reaction mixtures are a t pH 3.0 with no added salt. The ratio R ranged between 0.9 and 1.8. The exact value of the ratio is only indicated for those experiments in which it significantly affected the computations. * NaC104 = 0.40 M . cHC104 = 0.063 M . R = 0.90. * NaC1O4 = 0.29 M . f R = 1.80. 0 Re-extraction of the aqueous phase with fresh CC&of the original IScontent gave a D of 0.024, which was unaltered by another re-extraction. A duplicate experiment yielded identical results. Treatment as described in note ( 8 ) reduced D to 0.0033. HClO4 = 0.0063 M . Treatment as described in note ( 8 ) did not alter D. At1 AtIC1-
+ C1-
+
AtIClC1- = AtClz=
+ I-
(17) (18)
We may expect reaction 18, like reaction 16, to proceed largely bo the left unless the ratio of chloride to iodide is very great. For the distribution coefficient we have D =
IC7
1
+ &(I-) + Kn(C1-)[1 + Kidcl-)/(I-)I
(19)
and again we predict a maximum in D as the iodide is varied at’ constant chloride. The “Dcalcd”values of Table V have been computed with K17 = 9 and KIB = 2.0 X K , has been corrected for
EVAN H.
330
salt concentration in the manner previously described, and the observed salt dependence again appears to justify the correction. As in the preceding section, no acidit,y dependence was observed between and 6 X M acid.
TABLE VI OF HALOGEKS AND INTERHALODISTRIBUTION CONSTANTS GENS (21 ”) IC = (XY)CCL/(XY)aq
TABLE V DISTRIB.VTIOS OF (IdCc14
I-
k3TATINE
I N TEE
c1-
I,-I--Cl-
SYSTEMa
c------D---Calod. Expt!.
x 1oj x 102 19.0 0.95 3.9 4.1 22.4 10.6 2.6 2.8 19.2 9.6 2.4 2.6 2.2c 0.84 1.5 1.6 10.6 2.1 530 100 0.35 0.33 9.5d 95 94 .53 .52 19 23.0 96 .37 .40 9.5d 5.8 95 .18 .I8 5.4 2.2 102 .I6 .I5 Unless otherwise indicated the HCIOa concentration was 0.063 M and no inert salt was added. The (I2)ccl4has been corrected by 1-2% for the amount extracted into the aqueous phase and for the formation of I&-. A small correct,ion for 1 3 - formation has been applied to the iodide concentration. NaCIOI = 0.40M. c NaC104 = 0.97 M. HC104 = 0.001 M . x 104 IS* 2.1” 195
Vol. 65
AkPPELlnlL4N
Discussion The values of Kz and Ks obtained in the IBr-Brsystem are compatible with Faull’s 25” values of 3.9 and 370, re~pective1y.l~In a more recent paper Pungor, et al., claim on the basis of potentiometric measurements that the complex formed between IBr and Br- has the formula IBr4-3.17 However, their interpretation is fundamentally in error, and correct evaluation of their data gives results consistent with Faull’s work. l8 The assignment of the species involved in the astatine reaction hinges on the assumption that we start with AtI. Although this assumption is a plausible one that leads to reasonable conclusions, we must remember that from a different starting compound an entirely different set of species would be derived to fit the data. The scatter of the astatine data is greater than might be desired, but may be inevitable in a system of this nature. Because of this scatter the constants can easily be in error by as much as lo%, and some minor reactions may have gone undetected. However, the wide range covered by the experiments makes it appear fairly certain that the principal reactions are those indicated. Table VI compares the extraction behavior of the various halogens and interhalogens. The astatine species fit in fairly well with the trend of decreasing extractability with increasing polarity. The agreement between At1 and IBr is particularly significant as support for the identity of the former. However, the extractability of AtBr is lower than we might have expected. It is of interest to note that when other halogens are absent the distribution of “zero-state” astatine between water and CCl4 has been found to vary erratically from one experiment to another, with D’s generally very much greater than those found (17) E. I’ungor, K. Berger and E. Schulek. J . I n o r g . NucZ. Chem., 11, 5G (19591. (18) E. 11. Apprlman, ibzd., 14, 308 (19GO).
XY
K
AtBr IC1 IBr At1 Br-
0.040 0.34‘ 4.3 5.5 27 86
4 a
This work.
Ref. a
16 a Q
9 9
25’.
in the present study.a This indicates that the interhalogen astatine compounds with which we have been dealing here are considerably more polar than the “At(O)” species formed in the absence of other halogens. The nature of the latter species has been discussed in a previous paper, in which it has been suggested that they are organoastatine compounds formed with i m p ~ r i t i e s . ~ In Table VI1 the stability constants of the known XYZ- polyhalide ions are intercompared. The complexes tend to become progressively more stable as the atoms involved become heavier and more polarizable, and symmetrical complexes are more stable than asymmetrical ones. The astatine complexes appear in quite satisfactory agreement with the others. TABLE VI1 EQUILIBRIUM CONSTANTS FOR THE REACTIONS XY(aq.) Z- = XYZ(21-25”)
+
XYZ -
c1, BrzC1IZCl AtICII2BrBr3IBrC1AtIBrIC12AtBrsIBr213-
AtI20 This work.
K
Ref.
0.12 1.4 3 9 14 17 43 120 170 320 440 800 2000
19 13 12 0
12 13 16 0
16 a 0
11 a
The IBr analog of equation 10 has an equilibrium Hence IBr is much more constant of 1.5 X extensively hydrolyzed trhan AtI. This accords with the rapid decrease in the extent of hydrolysis of the simple halogens as they grow heavier. We may rewrite equation 11 .4tI
+ 1/&r2 = AtBr + 1/21~
(20)
and compare it with IBr
+ 1/zC12= IC1 +
l/2Br2
(21)
In the aqueous phase, these reactions have respective equilibrium constants of 4.2 X lo4 (21”) and 270 (25”).16 The difference is surprisingly great. We may similarly compare the reactions (19) 111. 5. Sherrill and E, F. (1928),
Izard,
J . Am. Chem. Soc.. 60, 1GG5
SOLUBILITY ASD ESTROPY OF SOLYTIOSS OF GASESIS S'SRIOVS SOLVESTS
Feb., 1961
+ C1+ Br+ C1
+ + +
AtC12IAtBr2I= IC12Br-
331
prise after the striking photochemical reactions reported p r e ~ i o u s l yand , ~ we see once again that the influeiice of light on tracer-level reactions cannot be safely disregarded. n-hich have equilibrium constants of 2 X and 6 X lop3,respectirely, the last at 1.1 X Acknowledgment.-I wish to express my grati25 15,16 tude to Professor I. Perlman for his direction of this The photosensitivity of the astatine distribution research and to Professor Robert E.Connick for a in the prrsenre of IBr should come as no great sur- great, deal of helpful discussion. AtIC1ItIBrIBrCl
=
=
(18) (22) (23)
SOLUBILITY ASD ENTROPY OF SOLUTION OF He, S?,A, O?, CH4, C2He,CO, AND SF, I N VARIOUS SOLVENTS; REGULARITY OF GAS SOLUBILITIES BY T.KOBATAKE AND J. H. HILDEBRAXD Department o j Chemistrg, University o j California, B e r k d e y , Caltfornia Recezved August 28, 1960
The apparatus and proCareful measurements of gas solubility in selected solvents have been made in the range 5-30'. (-edureare described in some detail. The gas, solvent, mole fraction x 104 a t 1 atmosphere and 2 5 O , and the entropy of solution, cal. mole-'dg.-', respectively, are: N2/CS2 2.215, - 1.77; CHa/CS212.69, - 1.77, C02/CS232.80, -4.83; S F d CR, 9.245. -0.30: CO,/C,F,R 208.8. -7.53: CHI/C,F,C82.62. -3.40: He/C7F7F. 8.90. 5.30: SFR/C,F,, 224.3 -8.00: Kz/ (C4F-s)3N-34.901-0.54; x/(C4F9)3N 50.03,'- 1.71.; ~02j1C4F9);N52.0,' - 1.90;' C 0 2 / ( C a F g ) & 200, - 7.30; C2H&/(CaFs)8 332.7, -8.80; Oz/i-CsHls 28.14, - 1.32; C2Hs/i-CsHls293.8, - 10.15; SF6/i-C8Hls153.5, -7.45. These and many other figures are plotted as (a) entropy of solution us. -R In 5 2 : (b) log x2us. solubility parameters of solvents; (e) log xz us. force constants of gases. They show extensive regularities with high predictive value and theoretical significance.
The work here reported is a continuation of systematic studies of gas solubility in the light of regular solution theory extending over many years and recently greatly intensified. 1-5 Careful determinations by Reeves4 of the solubility of argon in
five non-polar solvents over a range of temperature yielded important information about the different temperature coefficients of gas solubility. Jolley and Hildebrands published values for partial molal volumes and gave quantitative relations between
G
4
2
0
3 I
-2
I8
-4
-6
-8
- 10 - 12 8
10
12
-R In 2 2 . Fig. 1.
14
lG
18
