NOTES
3886
observed in this case is still consistent if one assumes a transient form, 1 - e--kt*, to take into account light scattering as a function of molecular weight of the growing polymer. It was also noted that a Lineac pulse induced ion pairs in the liquid isobutylene as determined by collecting charge between the plates of a capacitor under an electric field of 4000 v./cin. An oscilloscope triggered by the Lineac beam monitored the charge collected. The current flowed only during the Lineac pulse and therefore consisted of electrons which were collected in times short compared to 5 psec. and positive ions which did not move appreciably in this time. The charge collected from the sample was typically 6.5 x 10+ coulomb as compared to the Lineac beam current which gave only 2.0 X lo-' coulomb, thus establishing the presence of induced ion pairs as distinct from the Lineac beam current.
Acknowledgment. It is a pleasure to acknowledge P. C. Hoe11 and A. van Roggen for designing the apparatus for the transient dielectric constant measurements and V. F. Damme for constructing some of the equipment.
These give a total correction' of -0.148 A-unit. All solutions were made up by weight. The water used had a conductance of 1.65 x the maximum solvent correction was 0.65%. The cell had a constant equal to 1.0115 f 0.0001. Bridge, cell, and methods have been described previously.8 The conductance data (3 runs) are summarized in Table I. In order to obtain limiting conductances, Table I : Conductance of Cesium Bromide in Water at 25" 104~
82.824 65.955 41,442 24.924 14.540 78.639 56.192 40.152
A
10%
A
146.85 147.64 149.12 150,41 151.50 147.06 148.21 149.20
24.447 13,136 99,290 71.182 48.769 27.465 15.101
150.46 151.66 146.19 147.42 148.65 150.21 151.41
extrapolation was made on a A'-c plot by the method of least squares, using the equationsg
+ Scl" - EC log c = + JC
A' = A (obsd.) A'
Conductance of the Alkali Halides.
X.
The Limiting Conductance of the Cesium Ion in Water a t 25"
by Claude Treiner,' Jean-Claude Justice, and Raymond M. Fuoss2 Con,tribution N o . 176.6 f r o m the Sterling Chemistry Laboratory of Yale Unizersity. Mew Haven, Connecticut (Received J u l y 1.6, 1964)
Several recent determinations of the conductance of cesium salts in water lead to values for the cesium ion conductance which disagree by more than the estimated errors of measurement : 77.20 from cesiuni iodid@ and 77.33, 76.46, and 76.92 from cesium chloWe present here data for cesium bromide, which give Ao(Cs+)= 76.77, which is in excellent agreement with the weighted average of the other determinations. The cesium bromide was used as received from the Harshaw Chemical Co. ("random cuttings," from fused salt]). It was stored over phosphorus pentoxide in an evacuated desiccator. Analysis by the flame photometer showed trace impurities as follows: 0.0370/, LiBr, 0.076% NaBr, 0.00370 KBr, and 0.032% RbBr. T h e Journal of Physical Chemistry
A0
(1) (2)
For the three runs, the values A 0 = 155.157 f 0.013, 155.135 f 0.009, 155.143 f 0.0'17 and J = 180 f 2, 186 f 2, 186 f 3 were found. These average to d o = 155.15 f 0.02 and J = 184 f 2. Correcting for the impurities, Ao(CsBr) = 155.00 f 0.02. Using Longsworth's value'o of 0.4906 for the transference number of potassium in potassium chloride, and Lind's value8 of 149.89 for Ao(KC1), we obtain XO (E(+)= 73.54. From Kay's extrapolations" of the data for potassium b r ~ m i d e , ' ~we - ~have ~ Ao(KBr) = 151.77; (1) DuPont Postdoctoral Research Fellow, 1963-1964; on leave of absence from the University of Paris. (2) Grateful acknowledgment is made to the donors of the Petroleum Research Fund, administered by the American Chemlcal Society, for partial support of this work. (3) J. E. Lind, Jr., and R. M. Fuoss, J . Phys. Chem., 6 5 , 1414 (1961). (4) W. E. Voisinet, Thesis, Yale University, 1951. (5) J. C . Justice and R. M . Fuoss, J . Phys. Chem., 67, 1707 (1963). (6) F. Accascina and M. Goffredi, University of Palermo, private communication. (7) 12. IT'. Kunze and R. M. Fuoss, J . Phys. Chem., 67, 914 (1963); see eq. 11. (8) J. E. Lind, Jr., and R. M .Fuoss, ibid., 6 5 , 999 (1961). (9) R. M. Fuoss, J . Am. Chem. Soc., 81, 2659 (1959). (10) L. G. Longsworth, ibid., 54, 2741 (1932). (11) R. L. Kay, ibid., 82, 2099 (1960). (12) B. B. Owen and H. Zeldes, J . Chem. Phys., 18, 1083 (1950).
NOTES
3887
subtracting the conductance of potassium gives Xo (Br-) = 78.23. Finally, from the corrected conductance of cesium bromide, we find ho(Cs+) = 76.77. A repeat rum was also made on the cesium chloride used by Justice,j this time after fusing the salt in a platinum boa1 in a muffle furnace. The salt was kept molten for several minutes and then allowed to cool. Evidently the earlier samples still contained a little water after vacuum drying, because we now obtain do = 153.31 by extrapolation of the data of Table 11, Table I1 : Conductance of Fused Cesium Chloride in Water at 25" 104~
A
8A
118.044 87,936 67.898 47.206 23,859
143.164 144.496 145,480 146.724 148.587
-0,017 0.028 -0.001 -0.006 -0,004
where the last column gives the difference between thle observed conductances and those calculated by th,e equation A = 153.310
95.65~"'
+ 26.2% In c
+ 138.8~ (3)
Applying the same correction (-0.258) as before for impurities gives A,(CsCl) = 153.05; subtracting the chloride ion conductance'5 of 76.35 gives h,,(Cs+) -76.70, in excellent agreement with the value from the bromide. Averaging 77.20 from the i ~ d i d e 76.92 ,~ from the chloride,6 and our present values of 76.70 and 76.77 from the chloride and bromide, respectively, we obtain h o ( C ~ + )= 76.!30 st 0.16. (13) G . C. Benson and A. 12. Gordon, J . Chem. Phys., 13, 473 (1945). (14) G. Jones and G . F. Bickford, J . Am. Chem. Soc., 5 6 , 602 (1934). (15) Correction to line 5 b'elow Table I1 of ref. 5: redace 73.52 by 76.35 (or Cl by E+).
The Use of Sodium Borohydride in Catalytic Deuterium Exchange Reactions'
by G. E. Calf and J. IL. Garnett School of Chemistrzi, T h e University of h'ew South Wales, Kensington, N . S. W . , Australia (Received December $8,1968)
The problems associated with hydrogen reduction and activation of platinum oxide2 and other transition
metal oxides3azbhave already been discussed in the development of the associative and dissociative r-complex substitution mechanisms4 for the metal catalyzed exchange of organic coiiipounds with heavy ~ a t e r . ~A) ~ different type of procedure for the reduction and activation of platinum oxide using organic compounds has also been reported.' This "self-activated" catahyst possesses certain advantages in isotopic hydrogen exchange experiments especially when combined with either ultraviolet or y-radiation.* It is the purpose of this present publication to report the use of a new method for the preparation of active transition metal catalysts for exchange reactions, namely, reduction in aqueous media with sodium borohydride. Brown and B r o ~ nhave ~ ~ already '~ mentioned that the treatment of platinum metal salts with aqueous sodium borohydride yields finely divided black preci pitates which are active catalysts for the hydrogenation of olefins. However, the exchange properties of these catalysts have no1 been investigated but should be important since the activity of the catalyst, particularly the site effect, depends markedly on the method of reduction and actival ion.* Two types of metal catalyst systems have been studied, the water-soluble transition metal oxides and the soluble chloride salts. Benzene and ethylbenzene have been used as representative aromatic systeiiis whde hexane and cyclohexane were examined as examples of aliphatic reactivity.
Experimental Apparatus, general procedures, and low voltage mass spectrometric analytical techniques have been outlined in an earlier publication.2 For the hydrogen runs, reactions were performed with metallic oxide (100 mg.) prereduced with hydrogen or deuterium, benzene (4.0 X mole), and heavy water (12.0 X mole) at a temperature of 130'' for 48 hr. as previously described. 4 5 I n the hydride reductions, sodiuiii borohydride (400 mg.) was added slowly to a suspension of the oxide (100 (1) Part XI of a serieis entitled "Catalytic Deuterium Exchange with Organics." (2) J. L. Garnett and W. A. Sollich, J . Catalysis, 2 , 339 (1963). (3) (a) J. L. Garnett, and W. A. Sollich, Nature, 201, 902 (1964); (b) J. L. Garnett and W. A. Sollich, to be published. (4) J. L. Garnett and W . A. Sollich, J . Catalysis, 2, 350 (1963). (5) J. L. Garnett and W. A. Sollich, Australian J . Chem., 14, 441 (196l\. (6) J. L. Garnett and W . 9. Sollich, ibid.. 15, 56 (1962). (7) J. L. Garnett and W. A. Sollich, J . P h y s . Chem., 6 8 , 436 (1964). (8) W. G. Brown and J L. Garnett, submitted for publication, (9) H. C. Brown and (2. A. Brown, J . Am. Chem. Soc., 8 4 , 1403 (1962). (10) H. C. Brown and C. A. Brown, ibid., 84, 1494 (1962).
Volume 68, Number 12 December, 1.9f;4
