17
A New
Deep
Chlorine
Violet
Compound,
(O ClF )n, 2
Dioxygen
3
Trifluoride
A. G. STRENG and Α. V. GROSSE Research Institute, Temple University, Philadelphia 44, Pa.
A new deep violet compound, (O CIF ) , was dis covered by reacting O F with CIF at 119° to 140° K. It is thermally stable up to 195° K. for over a year. The stability of its concentrated deep violet solution in anhydrous HF depends on the oxygen pressure. This solution has practically the same conductivity as HF and thus the compound is not an electrolyte. The compound is a very strong oxidizing substance, and reacts with NH , various hydrocarbons, and even ice at low temperatures. It seems to surpass even ozone as an oxidizer. 2
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2
3
n
2
3
The colored polyoxygen difluorides—0 F , 0 F (3, 4), and 0 F (2)—repre sent the most potent oxidizers known, since they are endothermic compounds of oxygen and fluorine. 0 F decomposes into 0 F and 0 at ~ 120° K.; 0 F into 0 F and 0 at about 100° K. In the decomposition reaction, regardless whether it proceeds with the formation of free O-F radicals or atomic oxygen, highly reactive species are formed. For this reason the addition of only 0.1 weight % 0 F to liquid 0 makes the mixture hypergolic with a wide variety of fuels, including H , at low tem peratures (5). Higher members of this series, such as 0 F and O F , may exist (2) and thus the abstraction offluorinefrom the lower members by means of a suitable reaction is of particular interest. The view has been expressed (2) that in such an abstrac tion reaction cyclic polymers of oxygen—i.e., 0 and 0 —may form, since the strengths of O-O and O-F bonds are similar. The red color of the polyoxygen fluorides is due to the O-O bonds, since the O-F bond in O F does not giveriseto any significant absorption in the visible spectrum. In this respect the colored O-O bonds in thefluoridesare different from the O-O bonds in the colorless H 0 , or H 0 and alkyl peroxides. In our studies (6) attemptingfluorineabstraction, 0 F was reacted with CIF. If the reaction is carried out without special precautions, the two substances readily react following the stoichiometric equation: 2
3
2
2
2
2
3
2
4
2
4
2
3
2
3
2
2
2
2
2
5
2
e
2
5
6
2
2
2
2
4
2
0 F 2
with Δ Η
298
2
+ CIF — 0
2
2
+ CIF3
= —30.1 kcal. per mole. 159
COLBURN; FREE RADICALS in Inorganic Chemistry Advances in Chemistry; American Chemical Society: Washington, DC, 1962.
(1)
160
ADVANCES IN CHEMISTRY SERIES
However, if the reaction is carried out under mild conditions, from just above the melting point of CIF (119° K.) up to 130° K., an intense violet colored intermediate compound of the elementary composition ( 0 C l F ) (referred to simply as 0 C1F ) is formed, in line with the scheme: 2
2
3
n
3
0 F + CIF — 0 C1F 2
2
2
3
Its color and hue are very similar to those of the organic dye methyl violet. At the beginning it was thought that the intense violet color may be due to the formation of blue ozone mixed with some unreacted red-orange 0 F , : 2
3 0 F + 3 CIF — 2 0 2
+ 3 C1F
3
3
It could be readily shown that no ozone formed, since the latter can be easily vacuum-distilled out of such a mixture. The 0 C1F was obtained in a purity of 81%, the other 19% being the nearly colorless C1F . 0 C1F is a solid, thermally stable up to 195° K. At this tempera ture it can be kept for over a year. It has a vapor pressure of less than 12 microns at 158° K.; at this pressure and temperature it dissociates into its components, which can be collected on a liquid nitrogen finger (77° K.). If thefingeris warmed up to 119° to 140° K., the violet compound forms again. The compound is insoluble in liquid O and 0 at 90° K., in liquid C10 F and C F at 140° K., and in liquid N F , CC1 F , and CC1F at ^ 1 6 0 ° K. It is soluble in CIF at 125° K., 0 F at 140° K., and C1F at 190° K. It is readily soluble in anhydrous HF at 190° K., forming a deep violet solu tion. The solubility is high and a 65 weight % or 23 mole % 0 C1F solution is not saturated at 190° K. This solution is not an electrolyte. A 0.5M solution of 0 C1F in HF had specific conductivity of 3.57 X 1(H ohm cm. at 195° K., while the pure anhy drous HF used had the same conductivity. After decomposition the residual clear and colorless solution of C1F in HF also had the conductivity of 3.57 X 1(H ohm cm. In contrast, a 0.5M solution of a typical electrolyte, KF in HF, has a specific conductivity of 86.0 ohm cm.- , or approximately 25,000 greater. Thus, the possibility that our violet compound might be ionic or saltlike, dissociating, for example, into ions, 2
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2
2
3
3
2
3
3
z
3
8
3
2
2
3
2
3
2
3
2
3
2
-1
3
-1
3
-1
-1
-1
1
[0 C1F ] 2
2
+
and F~
is excluded. The stability of the 0 C1F solution in anhydrous H F is much less than that of the pure compound. It shows a remarkable dependence on the partial pressure of 0 . At an 0 pressure of 1.0 to 1.5 atm. and at 195° K. the concentrated solution can be kept for many hours; when the 0 pressure is reduced to 50 to 20 mm. of Hg the deep violet solution decolorizes in a few minutes by decomposition to 2
2
3
2
2
HF
•0
O2CIF3 ••
2
+
CIF3
It is indicated that the easy decomposition is at least partly due to the formation of an intermediate complex: CIF3 + HF 0 C1F 3
2
u.v.
2
3
COLBURN; FREE RADICALS in Inorganic Chemistry Advances in Chemistry; American Chemical Society: Washington, DC, 1962.
STRENG AND GROSSE
163
Dioxygen Chlorine Tri fluoride
The color of the C1F solution increased appreciably with time. However, if the 0 pressure equaled 15 mm. of Hg, no violet compound was formed. (A check experiment with pure C1F , in the absence of 0 , also failed to produce any violet compound. ) If ozone, 0 , was used instead of 0 , in the same experiment, no violet com pound formed. Some 0 decomposed, because of the irradiation, as observed from the increase in total pressure. The addition of 0 to the system did not cause the formation of the violet compound. Evidently the heat of decomposition of ozone is sufficient to cause the decomposition of any violet compound formed. 3
2
3
2
3
2
3
2
Reactions of 0 CIF
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2
S
The violet compound is a very strong oxidizer, even at low temperatures. In this respect it is similar to the highly reactive ozone, which, for example, reacts with N H even at 150° Κ. (I). Usually no chemical reactions take place in a temperature range of 100° to 150° K. with the exception of free radicals or atoms, as has been strikingly demonstrated by H. Broida and his associates at the National Bureau of Standards. A study was made of the reactions of 0 C1F with N H , the hydrocarbons C H , C H , C H , and C H , H , and H 0 . In most casesfluorinehas a pref erential affinity for hydrogen and HF is usually formed. Reaction with N H . When gaseous N H is suddenly admitted to a reaction vessel containing 0 C1F at 90° K., reaction takes place with aflash,forming white solids and some nitrogen-containing gases, while the violet color disappears. If the ammonia is condensed first in the upper part of a reaction tube cooled to 90° K., the reaction proceeds slowly as the vessel is warmed to 150° to 160° K. Ammonia has a vapor pressure of about 1 mm. at 160° K. and reacts slowly as a gas with the solid 0 C1F . Under these conditions the reaction proceeds smoothly without any gas evolution, while the violet color disappears and a white solid is formed. Under the same conditions pure solid C1F reacts much more slowly; this is to be expected, since, in any reaction with a fuel, the components formed from 0 C1F —i.e., 0 and C1F —are activated by the endothermic heat of forma tion of 0 C1F ( Δ Η assumed to be equal to + 15 ± 10 kcal. per mole). Ammoniumfluorideand other ammonium salts, HF, HCI, and the oxy-acids of chlorine (either free or as ammonium salts) were identified among the reaction products. Hydrogenfluoridewas identified by vacuum distillation, formation of NaF.HF, and titration. Hydrogen chloride was identified through formation of silver chloride. Ammonia was determined quantitatively by Kjeldahl's method. The oxynitrogen acids or oxychlorine acids were identified qualitatively by Lunge's reagent. Anions of the oxychlorine acids—i.e., chlorite, chlorate, or perchlorate— were identified by reduction with zinc to chloride ion. In one experiment 0.25 gram of 0 C1F was reacted with about 0.10 gram of ammonia; 52 mg. of N H was found in the reaction product together with about 3 mg. of N (gas). Thus, about one half of the ammonia added formed ammonium salts. (This mixture of ammonium salts and oxidizers is potentially dangerous and can detonate!) Reactions with Hydrocarbons. W I T H C H . 0 C1F does not react with an excess of liquid methane at 90° K., or with gaseous methane at a pressure of 100 mm. of Hg at 150° K. During one hour there was neither a decrease in pressure nor a disappearance of the violet color. 3
2
4
2
6
2
4
6
6
2
3
2
3
3
2
3
3
2
3
3
2
3
2
2
3
3
298
2
3
3
2
4
2
3
COLBURN; FREE RADICALS in Inorganic Chemistry Advances in Chemistry; American Chemical Society: Washington, DC, 1962.
164
ADVANCES IN CHEMISTRY SERIES
Wrra C H . Ethane, in contrast to methane, when admitted to the violet compound at a temperature of 140° K., reacts immediately. The violet color dis appears and white solids are formed, but no gas is evolved—i.e., no formation of 0 , F , or CO is observed. 2
2
e
2
Hydrogenfluoridewas also identified. Wrra C H : C H . The reaction vessel containing 1.39 grams of 0 C1F was cooled to 120° K. and ethylene gas was introduced (ethylene has a vapor pressure of about 1.0 mm. of Hg at 120° K.) in portions of about 5 mg. at a rate of about 1 mg. per second. After an interruption of 1 to 2 minutes, new portions were added. 2
2
2
3
Under those conditions ethylene reacted immediately, causing decolorization of the violet compound and formation of the white solid products, while no measurable gas evolution—i.e., no formation of 0 , F , or CO—took place. Downloaded by UNIV OF BATH on July 4, 2016 | http://pubs.acs.org Publication Date: January 1, 1962 | doi: 10.1021/ba-1962-0036.ch017
2
2
On one occasion when ethylene was added at a higher rate, the reaction proceeded with aflamewhich extinguished itself as soon as the ethyleneflowwas stopped. A total of 0.179 gram of ethylene was added to 1.3 grams of 0 C1F ; the temperature of the bath after this addition was slowly raised at the rate of 1° to 15° per minute. No gas evolution was noticed up to 140° K. At 140° K. a violent explosion took place, shattering the reaction vessel and a large part of the reaction system. Evidently, intermediate or partly oxidized products were formed. 2
3
In all reactions of 0 C1F with hydrogen-containing substances, H F is the most likely reaction product. Carbonyl fluoride, COF , and other intermediate oxyfluorides—for example, oxalyl fluoride, C 0 F —may be formed. In view of the violent explosion which took place, it is also likely that some C-H-containing compounds were present. 2
3
2
2
2
2
Reaction with Hydrogen. During one hour at 90° to 120° K. there was no noticeable reaction between 0 C1F and hydrogen gas at a pressure of 100 mm. of Hg. Any reaction would be characterized by disappearance or change in the violet color or decrease in the pressure of hydrogen. 2
3
The nonreactivity of 0 C1F with hydrogen and methane parallels the chemical properties of ozone. Pure (100%) ozone can be mixed at —78° C. and even at room temperature with hydrogen and methane without reaction (7, 8). (The mixture 1.5 C H + 2 0 , at 804 mm. of Hg, showed at + 2 1 ° C. a pressure increase of 26 mm. of Hg on standing for 1.0 hour.) 2
4
3
3
From the present preliminary evidence it is likely that 0 C1F will be more reactive than ozone at low temperatures. 2
3
Reaction with Benzene. The violet compound reacts violently with a solution of benzene in HF at 195° K. A few milligrams of C H , dissolved in HF, were distilled over into a Kel-F reaction vessel containing a 1 to 2% solution of 0 C1F in HF, and frozen on the walls above the 0 C1F solution. The tube was then warmed up to 195° K.; the melting HF began to run down, carrying the C H . Sparks were observed when the C H came into contact with the 0 C1F solution and the violet color disappeared rapidly. Reaction with Water. To test the reactivity of 0 C1F with H 0 , pulverized ice, cooled to 90° K., was added to the 0 C1F contained in a tube and the tube was slowly warmed. A visible reaction started at about 130° K. with gas evolution and formation of a white solid. Oxygen was liberated and HF and ClOH (or C10 H ) were formed. The reaction proceeded much faster at higher temperatures. e
e
2
2
3
3
e
e
e
2
2
2
3
3
2
3
2
COLBURN; FREE RADICALS in Inorganic Chemistry Advances in Chemistry; American Chemical Society: Washington, DC, 1962.
e
STRENG AND GROSSE
Dioxygen Chlorine Trifluoride
165
Conclusions Further studies of this very interesting compound, as to both its physical properties and structure and its chemical reactivity, are indicated.
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Literature Cited (1) Grosse, Α. V., Streng, A. G., Project 7-7968, Research Institute of Temple University, Tech. Note 4 (Aug. 1, 1957); Contract AF18(60)-1475. (2) Grosse, Α. V., Streng, A. G . , Kirshenbaum, A. D . , J. Am. Chem. Soc. 83, 1004 (1961). (3) Kirshenbaum,A.D., Grosse, Α. V., Ibid., 81, 1277 (1959). (4) Kirshenbaum, A. D., Grosse, Α. V., Aston, J. G., Ibid., 81, 6398 (1959). (5) Riehl, W. Α., Perkins, H., Stokes, C. S., Kirshenbaum, A. D . , ARS Journal 32, 384-7 (1962). (6) Streng, A. G., Grosse, Α. V., "Addition and Substitution Products of Oxygen Fluo rides," 1st and 2nd Annual Reports for Office of Naval Research, Contract Nonr 3085(01), Research Institute of Temple University, Jan. 3, 1961, and Jan. 19, 1962. (7) Streng, A. G., Grosse, Α. V., A D V A N . C H E M . SER., NO. 20, 40 (1959). (8) Streng, A. G., Grosse, Α. V., J. Am. Chem. Soc. 79, 3996 (1957). RECEIVED May 16, 1962. Research sponsored by the Office of Naval Research, Contract Nonr 3085(01).
COLBURN; FREE RADICALS in Inorganic Chemistry Advances in Chemistry; American Chemical Society: Washington, DC, 1962.
