NOTES
'1'abie I :
1665
Koto-kinetic
Ethyl Alcohol (dy--Tensiometer ring diameter, mm
5.48 6.18 7.38 8.53 10.38 13.58
su
'--'
c
Rotation frequency, rev/min 58 70 100
0
40
22.33 22.36 22.34 22.33 22.32 22.33
22.41 22.43 22.40 22.39 22.41 22.43
22.50 22.49 22.49 22.50 22.47 22.49
22.56 22.53 22.56 22.54 22.52 22.54
22.72 22.73 22.75 22.73 22.75 22.74
We have also tested the ability of several solid metal chlorides to catalyze vapor phase Friedel-Crafts reactions. 143
23.15 23.15 23.16 23.14 23.11 23.14
Table 11: Roto-kinetic Surface Tension of Butyl Alcohol (dynes/cm) at 21' Tensiometer ring diameter, mm
0
40
5.48 6.18 7.38 8.53 10.38 13.58
24.62 24.65 24.64 24.61 24.63 24.63
24.72 24.74 24.74 24.68 24.68 24.71
Rotation frequency, rev/min 58 70 100
24.80 24.80 24.76 24.79 24.79 24.79
24.85 24.84 24.86 24.88 24.82 24.85
25.05 25.07 25.05 25.08 25.04 25.06
143
25.55 25.59 25.58 25.55 25.57 25.56
At the temperature where the roto-kinetic effect disappears, there is a phase transition to an isotropic liquid phase. No existing mathematical theory is suitable to explain the surface phenomena described above.
Exchange of Chlorine between Hydrogen Chloride and Metal Chlorides1v2 by J. R. Wilson and J. E. Willard Department of Chemistry, University of Wisconsin, Madison, Wisconsin (Received A p r i l 19, 1966)
The exchange of halogen atoms between gaseous covalent molecules and a number of solid metal halides has been ~ b s e r v e d . ~ - lThat ~ such exchange should occur is in some ways surprising. There is no detailed knowledge of the nature of metal halide surfaces or adequate theory for predicting the probability of their reaction with covalent molecules. With the aim of determining whether there are significant differences
Experimental Section Gaseous HC1 was prepared from aqueous HC1(C136)by passing through PzOson a vacuum line. Its specific activity was determined in a glass annular counting jacket which surrounded a thin-walled Geiger tube. It was then exposed to the metal chloride sample in a 30-ml flat-bottomed quartz reaction vessel, which could be heated to any desired temperature. Following exposure it was returned to the counting jacket for determination of the activity. By repeated exposures of the HC1 to the sample, followed by activity determinations, the exchange of C136was followed as a function of time and temperature. Transfers were made by freezing the gas into a tube on the desired vessel, with the aid of liquid nitrogen. (1) This work was supported in part by the U. S. Atomic Energy Commission under Contract AT(l1-1)-32, by the W. F. Vilas Trust of the University of Wisconsin, and by a Danforth Foundation Fellowship. (2) Further details of the work are given in the Ph.D. Thesis of J. R. Wilson, University of Wisconsin, 1964, available from University Microfilms, Ann Arbor, Mich. (3) These include the exchange of chlorine between HC1 and NaCl,' AlCla: ZrCla,G and SnC14;' of chlorine between Clt and NaCl,' and AgC1;S of bromine between Brt and AgBr;g of fluorine in a number of gas-solid systems;10.11 of iodine between CHaI and AgI, F'dIz, TlIg, and PbI2;12 of bromine between CHaBr and BaBrt, CaBrt, and AlBr8;'a and of chlorine between alkyl chlorides and A1C13.14 (4) See for example and other references: (a) R. J. Adams and L. G. Harrison, Trans. Faraday SOC.,60, 1792 (1964); (b) L. W. Barr, I. M. Hoodlees, J. A. Morrison, and R. Rudham, ibid., 56, 697 (1960). (5) M. Blau, W. T. Carnall, and J. E. Willard, J . Am. Chem. SOC., 74, 5762 (1952). (6) B. P. Dahlstrom, Jr., and J. E. Willard, unpublished. (7) R. A. Howald and J. E. Willard, J . Am. Chem. Soc., 77, 2046 (1955). (8) F. J. Johnston, Ph.D. Thesis, University of Wisconsin, 1952. (9) (a) I. M.Kolthoff and A. S. O'Brien, J . Am. Chem. SOC.,61,3409 (1939); (b) I. M. Kolthoff and A. S. O'Brien, J . Chem. Phys., 7, 401 (1939); (c) N. Davidson and J. Sullivan, ibid., 17, 176 (1949). (10) (a) R. B. Bernstein and J. J. Katz, J . Phys. Chem., 56, 885 (1952); (b) R. M. Adams, I. Sheft, and J. J. Kats, Proc. Intern. Conf. Peaceful Uses A t . Energy, 8nd, Geneva, 20, 219 (1958); (c) I. Sheft, H. Hyman, R. M. Adams, and J. J. Katz, J . Am. Chem. Soc., 83, 291 (1961). (11) (a) T. A. Gens, J. A. Wethington, A. R. Brose, and E. R. Van Artsdalen, ibid., 79, 1001 (1957); (b) T. A. Gens, J. A. Wethington, and A. R. Brosi, J. Phys. Chem., 62, 1593 (1958). (12) I. Galiba, L. Latzkovits, and D. Gal, Magy. Kem. Folyoirat, 67, 323 (1961). (L3) G.-B.JCistiakowsky and J. R. van Wazer, J . Am. Chem. SOC., 65, 172Y (1943). (14) (a) C . H. Wallace and J. E. Willard, ibid., 72, 5275 (1950); (b) M. Blau and J. E. Willard, ibid., 73,442 (1951).
Volume 70, Number 6
M a y 1966
NOTES
1666
Table I: Exchange between HC1 and Metal Chlorides"
-looo
-'0320
LiCl NaCl KC1 MgClz CaC12 SrClz SrC12" BaCh BaClz" SCC13 YC13 Lac13 PrC13 NdCla GdCla DyCh YbCla HfCh COClZ CoC12 (subl)d Cn2C12 AgClcsb CdClz PbClz SbCla BiC13 GaC13/
50
80
20
50
> 7 - 2 0 0 0 % of activity transferred 80 20 50
Y
sn
~
3 20
0 50
-
0
~
80
10
b b 5 1
1 1
3
4
100
5 8
*
*
2
2 1
80 3
60
*
25
*
*
3
* *
2
100 6 2
*
15 120 10 5 3
35
6 5
1
2
*
*
1
15 1
6
80 2
6
25
*
5
100
1 75 25
30 13 40 5 10
55 20 40
3 3
5 2 5 2
35
*
10
20
Tic12 GeC13/ SnC12 a Numbers in the table show time in minutes required to achieve the per cent exchange indicated at head of column; * indicates too fast to measure. All of the measurements were made with 1.5 X lo-' mole of HCl in a 30-ml reaction vessel and a solid-to-gas C1 ratio of 38: 1 except for SbCL, BiCla, and CuzC12, where the ratios were 70: 1, 67: 1, and 18: 1, respectively. Estimated particle sizes were in the 5-p range unless otherwise noted. * Gave readily measurable exchange a t 380" and above. Annealing of NaCl in unFused samples. labeled HCl a t 600" for 2 hr prior to exposure to labeled HC1 did not change the exchange rate. This CoC12which had been sublimed a t 300°, forming sheets of stack-like crystals, gave only slow exchange at 300' or below, whereas the powder formed by dehydration of the hydrate gave rapid exchange a t 300". e AgCl also showed 20% transfer of activity in 5 min and 50% transfer Readily observable exchange occurs in 1 hr or less at -78". in 50 min a t 400".
'
Before and after each exposure to the metal chloride, the HCI pressure was determined. Normally it remained constant. Unless otherwise noted, 1.5 X 1 0 - ~mole of HCl(C136) was used in all runs, with sufficient metal chloride to give a ratio of chlorine in the gas to that in the solid of 1:38. With this ratio 97.4% of the Cl36 is present in the solid when equilibrium distribution of activity is achieved. The NaCl, KCl, LiCI, CdClZ, and PbClz used were reagent grade commercial materials. The AgCl was a single piece cut from a sheet obtained from the Harshaw Chemical Co. Anhydrous BaCln, SrClz, MgC12, CoC12, YCl,, and ScClB were prepared by dehydration of the hydrates in vucuo. The MgC12, YC&, and ScCL were exposed to inactive HC1 at eleThe Journal of Physical Chemistry
vated temperature prior to use in order to convert any hydroxide to chloride. The rare earth chlorides were prepared by treating the oxides with CCl, vapor at 500-600". Commercial CuzClz was purified by recrystallization, and BiCI8, SbCl,, and HfC14 were purified by sublimation. Compounds which are liquids at room temperature (TiC14, GeC14, and SnC14)were vacuum distilled into the reaction vessel. GaC1, was prepared by the reaction of HCl gas on Cia metal.
Results Exchange Studies. The data of Table I, based on curves of the type of Figure 1, show that exchange occurs for all of the chlorides tested, and give an indica-
1667
NOTES
L'
! i o ' !so' 'do'
llAl' EXPOSURE TIME, MIN.
'140'
Figure 1. Transfer of C1" from HCl(Cl*B) to AgCl and CdC12 as a function of time and temperature. Ratio of C1 atoms in HCl t o C1 atoms in metal chloride is 1:38.
tion of the minimum temperature ranges at which it can be readily observed. The comparisons are qualitative rather than quantitative, since the samples were prepared by different methods and the specific surface areas and defect concentrations were not the same. Except as otherwise noted, the estimated particle sizes were in the 5-p range. A striking feature of the results is the fact that the alkaline earth chlorides all undergo exchange much more rapidly than the alkali metal chlorides, and that their exchange is readily observable at temperatures as low as 0.3 of the absolute melting point. This was true both for samples prepared by dehydration of the hydrates and for crystals of BaC12 and SrClz prepared by cooling from the fused state, to ensure minimum surface are&. The evidence2 indicates that the transfer of chlorine atoms at the surface of the samples of Table I was, in all cases, fast compared to diffusion of the atoms into the latt,ice. The most plausible mechanism for this rapid transfer involves attraction of the chlorine end of an HC1 dipole to a positive lattice site, followed by departure of the proton in combination with a chlorine ion from another site. A mechanism of this type, involving induced dipoles, has been suggested to explain the fact that cc14 exchanges chlorine readily with the ionic surface of aluminum chloride, but not with dissolved or gaseous aluminum chloride.14& The rapid exchange of HC1 with the covalent species SnCL, TiCl,, GaC4, and GeCI4 at -78' suggests that these compounds have ionic surfaces or that a different mechanism, such as complex formation, is available. We have found no significant correlation of the observed exchange rates with available lattice parameters of the chlorides tested.2 Friedel-Craf ts Studies. Studies with AlCld4 and with ZrC146 have shown that they are capable of cata-
lyzing vapor phase Friedel-Crafts reactions as well as exchanging readily with HC1. To determine whether such catalytic effectiveness might be a general property of metal chlorides which exchange chlorine with HCI, the catalytic ability of additional compounds was investigated. These were chosen to include one compound which undergoes extensive exchange with HC1 only at elevated temperature (NaCl), and five compounds representing different types which exchange at room temperature (BaC12, SrCL, ScC4, HfCI4,and PbC12). The NaCl, BaCI2,SrC12,and PbClz were each allowed to stand in contact with ethyl chloride and benzene vapors €or times up to 6 months at 140'. The catalyst was present in large excess relative to the organic reactants which were present in equimolar amounts. The yield of ethylbenzene was a fraction of a per cent at most. ScCb showed no catalytic activity when maintained with the organic materials for 18 hr at 100'. HfCL gave a 30% yield of ethylbenzene in 16 hr at 30'. It is concluded that the ability of an inorganic chloride to exchange chlorine with HCI does not give information about its catalytic efficiency.
Chemical Shifts of Methyl Protons in Methylated Polynuclear Aromatic Hydrocarbons' by I. C. Lewis U n i o n Carbide Corporation, Carbon Products Division, Parma Technical Center, Parma, Ohio 4.6130 (Received J u l y $0, 1965)
The proton chemical shifts in polynuclear aromatic hydrocarbons have been the subject of considerable interest. The large downfield shifts exhibited by aromatic protons have been attributed to the effects of circula' ing ring currents involving the T electrons.2a Aromztic proton shifts additionally reflect changes in the r-electron density at the attached carbon atom.2b The magnitude of the ring current effect has been accurately estimated for benzene.3 In the treatment of (1) This research was sponsored in part by the Air Force Materials Laboratory, Research and Technology Division, Air Force Systems Command, U. S. Air Force. (2) (a) J. A. Pople, W. G. Schneider, and H. J. Bernstein, "HighResolution Nuclear Magnetic Resonance." McGraw-Hill Book Co., Inc., New York, N. Y., 1959; (b) T. Schaefer and W. G. Schneider, Can. J . Chem., 41, 966 (1963).
Volume 70,Number 6
M a y 1966
