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suggesting that ions of like sign participate in the exchange. When the acid concentration was varied, the rate constant showed a maximum at about 1 f. CHEMICAL LABORATORY (k = 2.5) and decreased to 0.9 a t 3.9 f. This beUNIVERSITY OF CALIFORNIA BERKELEY, CALIFORNIA JAMES CASON havior doubtless results from the combiped effects FURMAN CHEMICAL LABORATORY of ionic strength and hydrolysis of thallic ion. VANDERBILT UNIVERSITY We have also observed the exchange in 0.2 f. NASHVILLE, TENN. FRANKLIN S. PROW hydrochloric acid and find that the rate is markRE:CEIVED OCTOBER14, 1947 edly greater than in perchloric acid. We are continuing these studies. THE EXCHANGE REACTION BETWEEN THE TWO We are grateful to the Los Alamos Laboratory, OXIDATION STATES OF THALLIUM IN PER- in particular to Mr. J. W. Starner and Mr. E. L. CHLORIC ACID SOLUTIONS Bentzen, for neutron irradiation of the thallium, Sir: We also are indebted to Dr. Norman Davidson for We have studied the exchange reaction between his interest and helpful advice. thallous and thallic ions in aqueous perchloric acid GATESAND CRELLIN LABORATORIES OF CHEMISTRY and wish to make a preliminary report of the re- CALIFORNIA INSTITUTEOF TECHNOLOGY sults. This reaction is of interest in that it in- PASADENA, CALIFORNIA GARMAN HARBOTTLE~ R. W. DODSON~ volves transfer of two electrons between the reactRECEIVED DECEMBER 8,1917 ing species and in that it is found to proceed a t a slow and measurable rate, in contrast to the sev(6) Now at Chemistry Department, Columbia University, New eral other electron-transfer exchange reactions York, N. Y. which have been reported to be fast.' Earlier studies of this reaction2J were handicapped by EXCHANGE REACTION BETWEEN THAL.LIUM (I) the short half-life of the radioactive tracer used AND THALLIUM ( I n ) IONS IN PERCHLORIC AND (ThC", half-life 3.1 min.) and gave results which NITRIC ACID SOLUTIONS are dficult to interpret. Sir: Using T1204.206 (half-life ca. 3 years), we have We have measured the rate of the exchange reobserved the exchange reaction and have investigated the dependence of the rate of exchange on action between thallium(1) and thallium(II1) the concentrations of thallous and thallic perchlo- ions in aqueous solutions of perchloric and nitric rates, on the acid concentration, and on the tem- acid and have found it to be slow and measurable. perature. The thallous perchlorate concentration The data from earlier work'.2 on this reaction are was varied from 0.003 f. to 0.015 f., that of thallic difficult to interpret because the short lived tracer, ThC" (3.1 m.), limited the duration of the experiperchlorate from 0.0006 f. to 0.003 f. The method employed was to mix stock solu- ments. Part of the T1204-206 (a. 3.5 y) used as tracer in tions of active thallic perchlorate and inactive our experiments was prepared by the TI@, p ) rethallous perchlorate in a stoppered flask immersed action in the Washington University cyclotron, in a constant temperature bath, to withdraw samthe rest by the Tl(n,r) reaction in the Oak Ridge ples a t intervals, and to determine the distribution pile. Our procedure was to mix acid solutions of of activity between the two oxidation states of (I) perchlorate (nitrate) and active thalthallium thallium. Thallous chromate was precipitated from the sample by the addition of a mixture con- lium (111) perchlorate (nitrate), remove aliquots taining chromate, cyanide, ethanol and excess am- a t definite intervals of time, separate the two oximonia. This method was found to give a reason- dation states, and assay and count the two fracably clean separation, and not to induce a sig- tions. Two methods of separation were used. nificant amount of exchange during precipitation. (1) Thallium (111) hydroxide was precipitated The activity in the thallous fraction was found with ammonium hydroxide; both fractions being to vary with time in the simple exponential man- subsequently weighed and counted as thallium ner expected for an exchange reaction occurring a t (I) chromate. (2) Thallium (I) bromide was preThe rate of exchange cipitated with sodium bromide solution, both chemical equilibri~m.~.~ was found to be proportional to the &-st power of fractions being weighed and counted as thallium the concentration of each reactant. The specific (I) broinide. A fast, incomplete, but reproducible exchange rate constant is 2.0 moles-' liter hours-' a t 49.5' (perchloric acid 0.4 f.). The experimental ac- was induced a t the time of separation. The intivation energy is 12 kcal./mole. The addition of duced exchange (exchange measured a t zero time) a neutral salt (LiClO, 0.6 f.) increased the rate, could be varied from 45 to 70% for the hydroxide separation and from 8 to 13% for the bromide ( 1 ) See for example G T.Seaborg, Chcm Rcu , 27, 199 (1940). separation by adding the reagents in a different (2) J. Zikler, Z . Physsk, 98, 669 (1936),el al.
It would appear, however, that the absence of rings and quaternary carbons in phthioic acid has hardly been demonstrated.
(3) V Majcr, 2.ghyrik Chcm , A119, 51 (1937). (4) H A C. McKay, Nofurc. 149, 997 (1938) (6) R B Dullleld r a d M Cmlvm, Tuis JorrnNbL, 91. 557 (1046).
( 1 ) J. Zirtler. 2. Physik, ST, 410 (1984); 98, 76 (1936): 99, 669 (1986); 2. ghysih Clem., AlST, 103 (1940). (2) V. Mnjer, ibid.. A1T9, 61 (1987).
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order OT a t different rates. However, the induced exchange was reproducible when conditions were held constant so we were able to correct for it using the equation % exchange == % exchange (measured) - % exchange (induced) (100) 100 - yo exchange (induced) The corrected values (always three or more excluding the value a t zero time) obeyed the exponential exchange law.',' The half-times for the exchange rates are summarized in Table I. As expected the exchange rate is not dependent on the method of separation when proper account is taken of the induced exchange.
Hg' are each bound to two boron atoms. Each boron atom has three boron neighbors at 1.74 f 0.04 kX and one hydrogen neighbor a t 1.34 * 0.04 kx. In addition, B4, B4', B4" and B4"' each has a boron neighbor a t 1.96 * 0.04 kx and another hydrogen neighbor a t 1.54 * 0.04 kX; B1, B:, Bz, Bz', each has two boron neighbors a t 1.96 * 0.04 kx: BI and Ba', each has another hydrogen neighbor a t 1.34 * 0.04 kX. 45'
TABLB I TI(1)-TI(II1)EXCHANGE RATES 0.0244 f . Tl(I), 0.0244 f . Tl(II1) Acid
Temperature
Method of separation
Exchange half-tim; hr.
1.0 f. "01 1 . 5 f. HNOr 1.5 f . "0% 1 . 5 f . HClO, 1 . 5 f . HClO' 1 . 5 f . HClO, 2 . 5 f . HClO, 3 . 5 f . HClO,
25°C. 24.8 * 0.2" 24.8 * 0.2" 24.8 * 0.2" 24.8 =t0.2" 24.8 * 0.2" 24.8 * 0.2" 24.8 f 0.2"
Bromide Bromide Hydroxide Hydroxide Bromide Bromide Bromide Brornitlc
2.5 * 0.2 1.8 * 0. 1.6 * 0 . 2 36 * 4 35 * 4 33 * 4 45 * 4 67 * 5
M.
O=BORON I 0 :HYDROGEN
Fig. 1.
We are extending this work to determine the effect of temperature, ionic strength, and concentrations of the reactants on the exchange rate.
Each boron atom is bound to five or six other atoms, but the bonds are not all equivalent. In(3) H. A. C. McKay, Nalurc, 119, 997 (1938). asmuch as a bond distance of 1.96 k X has about (4) R. B. Duffield and M. Calvin, TaIs JOURNAL, 68, 557 (1946). half the "bond number"2 of a bond distance of DEPARTMENT OF CHEMISTRY 1.74 kX, one can say that each boron forms five WASZINGTON UNIVERSITY REN&J. PRESTWOODbonds of bond number 0.60. The corresponding Sr. LOUIS,M i s s o m ARTHURC. WAHL radius, R(0.60) = 0.87 kx. Consequently, R(l) RECEMX DECEMBER I 10, 1947 = 0.80 kX in agreement with Pauling.2 This structure for BloHlr gives excellent agreement with the observed X-ray diffraction intensiTHE STRUCTURE OF THE DECABORANE MOLECULE ties and also with the electron diffraction observasir: tions of S. Bauer.a A detailed discussion of the determination of the We axe studying the structure of crystalline decaborane, BIOHl,,by single crystal X-ray dif- structure of crystalline decaborane will be pubfraction methods. We have established the ap- lished soon. (2) L.PaUbg, THIS JOURNAL, 69, 542 (1947). proximate positions of the ten boron atoms and (3) S. Bauet, ibid., TO, 116 (1948). four of the hydrogen atoms, and have assigned probable positions to the remaining ten hydrogen RESEARCH LAFIBORATORY JOHNS. KASPER C. M. LUCHT ELECTRICCOMPANY atoms. (Hydrogen atoms are well resolved in GENERAL SCHENECTADY, NEW YORK. DAVIDHARKER fourier sections.) RECEIVED JANUARY 21,1948 The BlOHI4 molecule has the symmetry &mm2. The bond distances are as follows (see figure): B1-Bl', Bl-BI, B2-Bs, Bn-B,, BrB4, are HETEROGENEITY OF CRYSTALLINE BETA-LACTOGLOBULIN all 1.74 t0.04kX; Bl-Bz and B4-B4' are 1.96 f 0.04 m; B4-H4 is 1.34 f 0.04 kX,l and all other Sir : B-H distances axe assumed the same, except B4That crystalline &lactoglobulin is not a homoHs which is assumed to be 1.54 0.04 kx. (B4- geneous protein was indicated by the solubility B4'" and BI'-B~' are 2.76 * 0.04 k X and are not measurements of Gronwall' and by the electrobond distances.) Each hydrogen atom, except HII phoretic results of Li.% Our experiments with and He' is bound to a single boron atom; HIIand (1) Grbnmll, Compt. mend. haw. lab. Carlsbw;. S4, no. 6-11. 188 f
and H P ' werelocated on an electron density map; (1) Hd, Ed', the position. of the other hydrogen atom are aasumed.
(1042). (2) Li,
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68, 2746 (1946).
