NOTES
Sept., 1959 zinc, such as Zn20. Iiighrani and Drowart3 examined mass spectrometrically the products from a Knudsen cell containing a mixture of Zn and ZnO at temperatures from 1200 to 1400°K., but detected no lower oxide of zinc. We are therefore inclined to explain the fast evaporation of ZnO by Zn vapor as a true catalytic effect on the rate of decomposition of the solid oxide. The reactions concerned in flowing Zn and 0 2 may well be *ZnO(c) ZnO(c)
+ Zn(g) + 02*(g)
+ *Zn(g) + Ozk)
ZnO(g) --+ ZnO*(g)
--+
(1) (2)
Reaction 2 is likely to have a higher activation energy than reaction 1 since it involves the breaking of the strong 0-0 bond, whereas when a Zn atom from the gas phase strikes the ZnO surface it can readily remove an 0 atom by a reaction with low activation energy. This is a curious and unusual type of catalysis which involves the c.atalysis of a physical change (vaporization) by a chemical reaction, the exchange process a t the surface. The subsequent reaction would be either precipitation of ZnO or 2 ZnO --+ 2 Zn
+
0 2
(3)
(3) M. C. Inghram and J. Drowart, private communication.
SPECTROSCOPIC EVIDENCE OF TRIPHENYLMETHYL CATIONS ON A CRACKING CATALYST BYHECTOR RUBALCAVA~ Union Oil Company of California, Research Department, Brea, California Received February 16, 1969
This communication is a preliminary report of spectroscopic and chemical observations of the formation of triphenylmethyl cations on a silicaalumina catalyst from the reaction between the catalyst and triphenylmethanol. The sequence of infrared spectra shown are of a disc2raof compressed, finely powdered silica-alumina (approximately 40 mg./cn~.2thickness) in which triphenylmethanol has been dispersed. The sequence shows the development of an absorption band a t 7.32 p as the dehydration of the disc, by evacuation a t pressures of the order of 10 p Hg a t 25", progresses in an " i n situ" cell. Essentially the same changes were observed when the disc was dried by passing dry air over it. The appearance and growth of the band were accompanied by the appearance and intensification of a yellow color in the disc. Exposure of the disc to the air in the room caused both the yellow color and the absorption band to disappear. The changes were reversible. Sharp and Sheppard4 have discussed recently the infrared spectrum of the triphenylmethyl cation and show in their spectra that one of the strongest absorption bands of the ion falls a t about 7.4 p (ea. 1360 cm.-l). Although triphenylmethanol does have weak absorption bands in the (1) Department of Chemistry, University College, Dublin, Ireland.
(2) R . H. Lindquist and D. G. R.ea, paper presented before the Physical and Inorganic Division of the American Chemical Society, September, 1957. (3) Personal communication, Dr. W. A . Pliskin. (4) D. W. A. Sharp and N. Sheppard. J . Chew. Soc., 674 (1957).
1517 I
I
-
Wave length. Fig. 1.-Sequence of spectra showing the growth of the triphenylmethyl cation band a t 7.32 p upon catalyst dehydration.
region we examined, they are, as can be seen in the first curve of Fig. 1, too weak to be seen under the conditions used in our experiments. The yellow color of the triphenylmethyl cation in several different media, e.g., in polar solvents such as acetone and acetonitrile, or as the crystalline perchlorate, is mentioned in ref. 3. We find that an intense yellow color appears immediately upon mixing moderately dry, powdered silicaalumina catalyst with a solution of triphenylmethanol in benzene or isooctane. If the experiment is performed with an alcoholic solution, the: color does not appear until the resulting mixture is dried. The mixtures of catalyst and triphenylmethanol may be dried by gentle heating, or by the above-mentioned means. Storage of the mixture over a desiccant preserves the color. The color disappears upon contact with water, alcohol or moist air, and will re-appear after subsequent drying. These facts are consistent with the reaction (CeHs)3COH
+ HOX
(C6Hj)aC'OX-
+ HzO
HOX represents the catalyst acid and OX- the anion. The reaction
+
( CBHS)BCX RIXn
(C,Hs)& +MX-n+ I
is well known.4 The spectra were obtained with n modified Beckmnn IR-2A spectrophotometer with a NaCl prism. The tripheiiylniethanol was Eastman-Kodak White Label grade, and the catalyst was Houdry type M-46. Further work on this system is under way. Invaluable discussions with Mr. R. C. Hansford and Dr. F. C. Seubold we acknowledged gratefully.
THE DOUBLE BOND ISOMERIZATION OF OLEFINS BY HYDROGEN ATOMS' AT -195' BY MILTOND. SCHEERA N D RALPHK L E I N ~ National Bureau of Standards, Washington, D . C . Received March PI, 1069
It has been established that the primary procew in the reaction of hydrogen atoms with 1-olefins is addition to the terminal carbon to form a second(1) This research was performed under the National Bureau of Standards Free Radical8 Research Program, supported by the Department of the Army. (2) Guest Scientist, Olin-Mathieson Chemical Corp.
