NOTES
2475
sorption of Kr on LiF calculated from the isotherms at -183 and -19.5' are shown in Figure 2. The AH, value is the heat of vaporization of liquid krypton at its normal boiling point.* If one takes the initial higher heat as due to some surface heterogeneities and the latter part of that including contributions of lateral interactions, then the minimum in the heat curve probably corresponds to the adsorption of individual molecules on the surface. This confirms the above prediction.
Acknowledgment. The author is grateful to Dr. J. T. Iiunimer of this laboratory for many helpful discussions during the course of this work. (8) "Selected Values of Chemical Thermodynamic Properties," National Bureau of Standard Circular 500, U. S. Government Printing Office, TVashington, D. C .
The Photochemistry of A2s5-Bicyclo[2.2.lIheptadiene'
by B. C. Roquitte2 Division of Pure Chemistry, National Research Council, Ottawa, Canada (Received J a n u a r y 86, 1966)
Theoretical calculation indicates that there is interaction between the two isolated double bonds in the lowest excited state of A2r5-bicyclo[2.2.l]heptadiene, BCHD [2.2.1]; recent experimental observation that BCHD in ether solution upon irradiation with ultraviolet light causes isomerization to quadricyclene lends support to this vie^.^ It is quite likely that the excited
excited state
species involved in the liquid phase photolysis may be stabilized by collision to give a product which could be entirely different from that of the gas phase photolysis, or an altogether different excited species may be present in the gas phase. This work was undertaken in order to gain better understanding of the excited state involved in the photodecomposition of BCHD, in particular, the behavior of such an excited species in the gas phase. Preliminary work indicated a difference between the behavior of the excited species in the liquid and that in the gas phase, depending upon the amount of excess energy present .5
Experimental I n order to avoid the mercury-photosensitized decomposition of BCHD, a mercury-free vacuum system which employed a two-stage oil diffusion pump backed by a mechanical pump was used. The reaction system, consisting of a cylindrical quartz cell 10 cm. long and 180 cc. in volume, connected to a piston-type circulating pump used for mixing reagent gases, and a diaphram gauge used as a null-type manometer, was enclosed in an air thermostat controlled to * l o . The light source was a mercury resonance lamp used previously in this laboratory,6 operated at a current of 60 ma. to obtain maximum intensity. A Corning 7910 filter was used in conjunction with the lamp to eliminate the 1849 radiation, so that the actinic light consisted mainly of 2537-A. radiation. Two runs were made using no filter to investigate the effect of wave length on the product distribution. The light intensity was varied by interposing a wire-gauze screen between the light source and the reaction cell, and the relative intensity was measured with a 935 phototube connected to a sensitive galvanometer. Spectrograde acetone (Eastman Kodak Co.) was used as a gas phase actinometer. BCHD [2.2.1] purchased commercially from Chemical Intermediate and Research Laboratories, Ohio, was fractionated and a middle fraction further purified by gas chromatography. The purified sample on analysis by gas chromatography was estimated to be 99.9% pure and was degassed and stored under vacuum The standard sample of cyclopentadiene (used for the calibration of the gas chromatograph) was synthesized from dicyclopentadiene (Eastman Kodak Co.) . Sitric oxide (Matheson 98%) was purified by bulb-to-bulb distillation from - 160 to - 196". Oxygen, helium, and hydrogen (all Matheson C.P. grade) were used directly from the cylinder. Sulfur hexafluoride (Xatheson 98.7%) was subjected to bulb-to-bulb distillation before use. Ethyl ether (Mallinckrodt) and cyclohexane (Phillips research grade) were distilled under vacuum, and only middle fractions were used. After irradiation, the reaction mixture was condensed out of (1) Issued as National Research Council No. 8520. Presented at the 47th Canadian Institute of Chemistry Conference, Kingston, Ontario, June 1-3, 1964. (2) Radiation Research Laboratories, Mellon Institute. Pittsburgh 13, Pa. (3) C. P. Wilcox, Jr., S. Winstein, and W . G . Mchlillan, J . Am. Chem. SOC.,82, 5450 (1959); R. B. Hermann, J . Org. Chem., 27, 441 (1962) ; B . C. Roquitte, unpublished data. (4) W. G. Dauben and R. L. Cargil, Tetrahedron. 5 , 197 (1961). (5) B. C. Roquitte. J . Am. Chem. Soc., 85, 3700 (1963). (6) R. -4. Back and D . \'an Der Auwera, Can. J . Chem., 40, 2339 (1962).
Volume 69, Xumber 7
J u l y 1966
NOTES
2476
the reaction zone into an ampoule and sealed off under vacuum. When noncondensible gas was added, the contents of the reaction cell after photolysis were passed through two traps a t - 196" (when SFe was used, trap temperature was - 130") and noncondensibles discarded. The condensible portion was then transferred into the ampoule and sealed off. The products from the ampoule were introduced into the inlet system of an F d' ;\I temperature-programmed gas chromatograph Model 720 by means of a special crushing device. A silicon grease column (7.9 m., 25% by weight on Celite) was used for quantitative analysis of the products. In addition, a Reoplex column (18% by weight on Celite) and a Ucon fluid column (Byoby weight on Celite) were used for the identification of the products. Each product was confirmed by mass spectrometric analysis. The identity of cyclopentadiene was also corifirnied by ultraviolet absorption7 [A, 4000 A. ( e 3000)]; the infrared spectrum of product cyclopentadiene was also found to be identical with that reported.8 Toluene was identified in the gas chromatograph by its retention time.
are given in Table I. In order to examine the effect, of inert gas on the decomposition, a variety of gases was added, and the results are tabulated in Table 11, which also includes the results of the photolysis in ether and cyclohexane solution.
Results
The yields of the products, cyclopentadiene and acetylene, are plotted as functions of time in Figure 1. From the linearity of the plots, it may be concluded that there was no change in the rate of formation of either of the products over the range of conversion used in this study. At higher conversion, the rate of production of cyclopentadiene decreased because of secondary decomposition.
The photolysis of BCHD with 2537-8. radiation in a mercury-free system a t temperatures of 27 and 57" and initial pressures from 4 to 31 mm., in the presence and absence of added gas, gave acetylene and cyclopentadiene i n equal amounts; toluene was detected as a minor product. In most of the experiments, the conversion was approximately 0.1%; at higher conversiori, cycloheptatriene was $so a product. Since cyclopentaditxne absorbs 2537-A. radiation, a t higher conversion complications arose from its secondary decomposition. The results of the photolysis of BCHD ~~~~
Table I : Photolysis of BCHU under Various Conditions" Initial concn., moles/l X 10'
1 2 2 3 6 6 9 16
07 29 65 42 24 27
dCsHz
0 40 0 50 0 50
81
0 49 0 50 0 54 0 49 0 49
3 94 2 26
0 48 0 54
28
Relative intensity, 'Z
QCKH~
27' 0 40 0 51 0 53 0 50 0 50 0 50 0 50 0 49
0 059 0 055
100 100 39 100 100 39 100 39
0 050 0 055
100 100
0 058 0 054 0 051 0 052
Table 11: Effect of Added Gas on the Photolysis of BCHD a t 27"" dC2Hz
0.52 0.50 0.42 0.42 ... ... 0.41 . . .
... 0.12 0.11
dCaHa
OtOl
0.51 0.49 0.41 0.41 0.49 0.42 0.42 0.48 0.39 0.14 0.13
0 056 0 048 0 050 0 050 0 055 0 051 0 053 0 053 0 051 0 042 0 052
a Initial concentration 6.84 X quanta/cc. sec.
Added gas. mm
Hz, 100 Hz, 300 Hz, 690 He, 650
NO, 10 NO, 600 02, 612 SFs, 44 SFB,400 Ether sol. Cyclohexane sol.
M. 10
=
4.21 X
lOI3
Discussion The ultraviolet absorption spectrum of BCHD has not been studied in detail. Qualitatively, the absorption begins a t about 2700 A. and exhibits a shoulder a t 2300 fi. and several bands with fine structure between 2260 and 1990 A.3 At 2537 8 . , the absorption was found to obey Beer's law accurately in the pressure range 4-31 mm. The fact that photolysis of BCHD with 2537-,i. radiation produced acetylene and cycloperitadiene in equal amounts and a small amount of toluene suggests that in the gas phase BCHD exhibits no less than two primary processes
57"
a
0 49 0 52
I o = 4.21 X 1013quanta/cc. sec.
The Journal of Physical Chemistry
(7) L. W. Pickett, E. Paddock, and E. Sackter, J . Am. Chem. SOC., 63, 1073 (1941).
(8) J. Thiec and J. Wiemann, Bull. Soe. Chim. France, 207 (1958).
XOTES
2477
involve monotadicals. In addition, since oxygen had no effect on the product yields, it might be concluded that long-lived triplets were not involved in the photochemistry of BCHD. The decomposition probably proceeds through the intermediate formation of highly reactive biradicals I and 11. The decomposition of bi-
I1
I11
radical I could give cyclopentadiene and acetylene, while biradical I1 could rearrange to give biradical I11 and finally toluene. The rearrangement of a biradical of the above type is known in terpene chemistry.9r10
Acknowledgment. The author is grateful to Drs. K. 0. Kutschke and R. A. Bgck for their interest in this work. (9) H. Pines and J. Ryer, J . Am. Chem. SOC.,77, 4370 (1955). (10) R. L. Burwell, Jr., ibid., 73, 4461 (1951).
Time (minutes) Figure 1. Variation of rate of formation of cyclopentadiene and acetylene with time.
y-Radiolysis of Ammonium Perchlorate1*, by George Odian,IcTerese Acker, and Thomas Pletzke Radiation Applications Inc., Long Island City, New York 10111,
Since we were unable to observe any emission visually, it is assumed that the molecules of BCHD do not dissipate energy by fluorescence a t wave lengths -36007000 A. Over a range of pressure the total quantum yield (Tables I and 11) for decomposition was 0.55 f 0.02; thus, it seems likely that 45% of the excited molecules were internally converted to the ground state. While the photodecomposition of BCHD presumably proceeds via some excited state, the almost negligible effect of added gas and temperature and the independence of the quantum yields on the pressure indicate that any such excited species had too short a life to suffer collisional deactivation under our experimental conditions. In view of the energy (112 kcal.) per quanta of 2537-A. radiation, this is not a t all surprising. This is also consistent with the fact that in the liquid phase (Table 11), where one would expect very many more collisions among the molecules, the quantum yields ( @ c C 1 H 1and @ c C awere ~ J lowered by a factor of 4. It is riot clear why the quantum yield for the production of toluene was not affected, unless it originates from a different electronic excited state altogether. It is to be noted that nitric oxide behaved as an inert gas in this system, which suggests that the decomposition did not
and Department of Chemical Engineering, Columbia University,
New York, New York
10027
(Received February 1 , 1966)
Although the radiolysis of various alkali and alkaline earth perchlorates has been extensively studied, 2, t h a t of ammonium perchlorate has received little attention. Freeman and co-worker~,~ in one of the few reports on the chemical products of ammonium perchlorate radiolysis, have found chloride, chlorate, nitrite, and nitrate to be present. We wish here to describe the results of our studies on solid ammonium perchlorate radiolysis. (1) (a) Presented in part at the 148th National Meeting of the American Chemical Society, Chicago, Ill., Sept. 1964. (b) The authors wish to acknowledge gratefully the support of this work by the Air Force Office of Scientific Research, Propulsion Division, under Contract AF 49(638)-1125. (c) To whom inquiries should be addressed: Department of Chemical Engineering, Columbia University, New York, N. Y. 10027. (2) (a) L. A. Prince and E. R. Johnson, J . Phys. Chem., 69, 359, 377 (1965); (b) L. A. Prince, Ph.D. Thesis, Stevens Institute of Technology, 1963. (3) H . G. Heal, Can. J . Chem., 31, 91, 1153 (1953); 37, 979 (1959). (4) (a) E. S. Freeman and D. A. Andersoh, J . Phys. Chem., 63, 1344 (1959); 65, 1662 (1961); (b) J. 9. Hyde and E. S. Freeman, i b i d . , 6.5, 1636 (1961); (c) E. 9. Freeman, D. A. Anderson, and J. J. Campisi, ibid., 64, 1727 (1960).
Volume 69, Number 7
July 1966
