COMMUNICATIONS TO THE EDITOR
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state is a highly polar charge-transfer one resembling the valence bond structure
and this conclusion is supported by experimental evidence that the analogous excited state of p-nitroaniline has a very large dipole moment.11 The charges are far enough apart to act independently on the solvent. When protolytic dissociation occurs, the charge on the anion RO- becomes delocalized and some bound solvent is released. It is worth remarking that density datal2 show that the electrically analogous dissociation of zwitterions of amino acids
+ O2C-R-NH3
+02C-R-NH2
+ H+
bX/d
L
1.0
2.0
I
3.0
I
4.0
I
5.0
J
6.0
VIA
(in water)
Figure 1.
also involves a small increase of Volume. Ward and Habgood'). The linear relation confirms the suggestion'J that the adsorption of carbon dioxide (like that of carbon monoxide) is essentially a polariDIVISIONOF PHYSICAL CHEMISTRY S. D. HAMANN zation effect caused by the electrostatic field due to AND INDUSTRIAL COMMONWEALTH SCIENTIFIC the cations in the zeolite. The X and Y series give RESEARCH ORGANIZATION separate lines indicating that the field strength calcuMELBOURNE, AUSTRALIA lations have not fully taken into account the differences RECEIVED MAY9, 1966 between the X- and Y-type zeolites. It is interesting to note that in the case of transition metal cation Y zeolites, the COS frequency is practically unchanged from the gasphase value, although the electric field Carbon Dioxide Adsorbed on was calculated to be very close to that in Mg2+-conLinde X and Y Zeolites taining zeolites. (11) J. Czekalla and G. Wick, Z . Elektrochem., 65,727 (1961). (12) H.H.Weber, Biochem. Z.,218,l (1930).
Sir: In a recent article,l Ward and Habgood reported on carbon dioxide adsorbed on Linde X zeolites. They found that in the alkali earth metal cation substituted zeolites the asymmetric stretching vibration of the adsorbed carbon dioxide was at a higher frequency than in the gas phase and dependent on the cation present. They attributed this shift to an ion-dipole interaction resulting in a linear adsorption of the C02 molecule. This phenomenon is very similar to our observation2 on the cation dependence of the vibration of adsorbed carbon monoxide, which we explained as due to a polarization of the carbon monoxide molecule in the electrostatic field of the cation. We also observed a frequency shift in the case of COZadsorbed on Linde Y zeolites, and we were able to put the field dependence on a semiquantitative basis. The method of calculating the electrostatic field in the neighborhood of the cation has been described p r e v i o u ~ l y . ~ ~ ~ Figure 1 shows the frequency of the asymmetric stretching vibration of adsorbed C02 plotted against the calculated field strength (filled circles represent our values, and open circles represent values from The Journal of Physical Chemistry
(1) 3.W. Ward and H. W. Habgood, J. Phys. C h m . , 70, 1178 (1966). (2) C. L.Angel1 and P. C. Schaffer,ibid., 70,1413(1966). (3) P. E. Pickert, J. A. Rabo, E. Dempsey, and V. Schomaker, Ades Congr. Intern. Catalyse, Se, Amsterdam, 1064,714(1965). Actual values of the field strength based on an improved model were kindly made available by Dr. E. Dempsey.
UNIONCARBIDE RESEARCH INSTITUTE UNIONCARBIDECORPORATION TARRYTOWN, NEWYORK
C. L. ANGELL
RECEIVED MAY19, 1966
The Reactions of Thermal Hydrogen Atoms with Ethanol and Ethanol Free Radicals at ??OK
Sir: The reactions of hydrogen atoms and trapped free radicals in alcohol glasses at 77°K have been the As a result subject of considerable (1) R. 5.Alger, et d., J. C h m . Phys., 30,695 (1959). ( 2 ) R.H.Johnsen, J . Phys. Chem., 65,2144(1961); 67,831 (1963). (3) P.J. Sullivan and W. 5.Koski, J . Am. Chem. Soc., 86, 159 (1964).
COMMUNICATIONS TO THE EDITOR
of a series of investigations involving the reactions of thermal hydrogen atoms with a variety of organic solids, as well as with irradiated ethanol glass, in the manner of Klein and Sheer,G we have made the following observations. (1) Thermal hydrogen atoms under these conditions undergo no appreciable reaction with solid ethanol. This is based on the observation that there is no pressure change observed during H atom bombardment and that no products detectable by flame ionization gas chromatography were observed. (2) When a sample of solid ethanol at 77°K which has previously received a total dose of 4.2 X 1020 ev/g of 3-Mev-peak X-rays was subjected, before melting, to H atom bombardment, G(glyco1) was reduced from 0.94 to 0.02 while G(a1dehyde) was increased from 2.64 to 4.70. Assuming that two a-ethanol radicals are required to produce one glycol molecule, this corresponds to a loss of 2 X 0.92 = 1.84 radicals, which is nearly equivalent to the increase in G(a1dehyde). These observations suggest that the following processes are significant in the radiolysis of ethanol glasses. Those H atoms which are thermalized diffuse freely through the matrix, but can react only by combination or with species other than the substrate ethanol; thus cyclic photochemical reactions resulting from the reaction of hydrogen atoms produced by the photolysis of trapped free radicals as suggested by Dainton’ are possible only when the radiation employed is energetic enough to produce hot hydrogen atoms. This point is currently under investigation, and preliminary results suggest that in methanol, light of wavelengths less than 3300 A is necessary to achieve this type of cyclic process, while light of wavelengths as long as 5400 A is capable of photolyzing certain of these trapped radicals. Glycols are produced by the combination of a-ethanol radicals subsequent to the softening of the matrix rather than by radical diffusion at 77°K. Otherwise, the bombardment by H atoms would not be likely to affect the glycol yield so drastically. H atoms react with a-ethanol radicals mainly by disproportionation rather than combination, which is attested to by the appearance of acetaldehyde in an amount essentially equivalent to the reduction in the glycol yield. The aldehyde which is produced directly by the radiation (G = 2.64) is not affected by the thermal H atoms at this low temperature. This suggests that this yield of aldehyde does not result from the disproportionation of ethanol free radicals but is rather the result of an ionic reaction or a unimolecular dissociation. This is in agreement with the observations of Myron and Freeman8 that scavengers do not lower the yield of aldehyde in the liquid state.
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These observations are a part of a general study of the reactions of thermal hydrogen atoms with the aliphatic alcohols which will be reported on in the near future. Acknowledgment. This work was supported in part by the U. S. Atomic Energy Commission under Contract AT- (40-1)-200 1. (4) J. Teply, A. Habersbergerova, and K. Vacek, Collection Czech. Chem. Commun., 30,793 (1965). (5) J. A. Leone and W. Koski, J. Am. Chem. SOC.,88,224 (1966). (6) R. Klein and M. D. Sheer, ibid.,80,1007 (1958). (7) F. S. Dainton, G. A. Salmon, and J. Teply, Trans. Faraday Soc., 61,27 (1965). (8) J. J. J. Myron and G. R. Freeman, Can. J . Chem., 43,381 (1965).
R. H. JOHNSEN A. K. E. HAGOPIAN H. B. YUN
DEPARTMENT OF CHEMISTRY FLORIDA STATEUNIVERSITY TALLAHASSEE, FLORIDA 32306 RECEIVED MAY25, 1966
The Radiolysis of Pure Decaborane-14l Sir: Preliminary results are herewith reported on the Corn y-ray radiolysis of pure decaborane in the solid state. This work was carried out using standard vacuum2 and gas chromatographic technique^.^^^ The results of this study indicate that the products of the radiolysis are hydrogen, diborane, pentaborane-9, and a polymeric substance. The polymeric substance has not yet been identified except that it is not the icosaborane-26 reported by Hall and Koski4 in their deuteron irradiation of decaborane-14. The yields of the gaseous products at 35” as a function of total dose are shown in Figure 1. The initial product yields in the linear region of these curves have G values for hydrogen, diborane, and pentaborane of 0.84, 1.70, and 0.15, respectively. The results shown in Figure 1 are typically what is to be expected from radiolysis as a function of dose except in the case of the diborane yield. It is felt that this unusual behavior of the diborane yield may be due to either radiolysis of the polymer produced or interconversion reactions between the diborane and unstable boranes such as tetraborane between the time of radiolysis and analysis of the ss~mples.~ (1) This research was supported in part by the Oak Ridge Associated Universities Inc. (2) S. Dushman, “Scientific Foundations of Vacuum Techniques,” John Wiley and Sons, Inc., New York, N. Y., 1962. (3) G. F. Shipman, Anal. Chem., 34,877 (1962). (4) L. H. Hall and W. S. Koski, J. Am. Chem. Soc., 84,4205 (1962). (5) The time here was of the order of 3-5 days a t a temperature of about 30’.
Volume 70, Number 7 J u l y 1966
