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Radical Reactions of Tetrafluorohydrazine JEREMIAH P. FREEMAN Redstone Arsenal Research Division, Rohm & Haas Co., Huntsville, Ala.
Tetrafluorohydrazine, N F , undergoes a variety of free radical reactions, including hydrogen ab straction to form difluoramine and coupling reac tions to form inorganic and organic difluoramines. Nuclear magnetic resonance data on these di fluoramines demonstrate the utility of this analyti cal tool in investigations in this field.
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The remarkable stability of the difluoramino radical which has recently been established quantitatively (8,14) was presaged by its early chemistry. In retro spect it is apparent that the formation of tetrafluorohydrazine from nitrogen tri fluoride under hot tube conditions (4) involved the formation of the difluoramino radical, from which it is more difficult to remove anotherfluorinethan from nitrogen trifluoride. At the time of the original synthesis, however, it could only be marveled at that N F , a compound much closer to nitrogen than N F , would survive conditions that decomposed the latter. It was also observed that N F decomposed in moist air to produce various nitrogen oxides. The origin of this reaction is undoubtedly the coupling of difluoramino radicals with oxygen, since undissociated N F should be unaffected by air. Finally, the remarkable conversion of "wet" nitrogen trifluoride to difluoramine (9) over hot arsenic, followed by the discovery that arsine was the hydrogen transfer agent (7), suggested that a radical abstraction reaction was occurring in the hot tube. In confirmation of this hypothesis a dependable method for the synthesis of difluoramine was found in the reaction of N F with mercaptans (7), which are known to be good hydrogen atom sources. 2
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3
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2NF - + 2RSH -* 2HNF + 2RS2
2
L-> RSSR Difluoramino radicals also abstract hydrogen from aliphatic aldehydes to produce difluoramine. In addition, the acyl radical thus generated couples with an N F radical to produce a new class of organic compounds, the 2V,2V-difluoramides (13): 2
RCHO + -NF RCO
+ -NF
2
2
-> RCO + HNF -> RCONF
2
2
12a COLBURN; FREE RADICALS in Inorganic Chemistry Advances in Chemistry; American Chemical Society: Washington, DC, 1962.
FREEMAN
Radical Reaction of Tetrafluorohydrazine
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Difluoramino radicals combine with a variety of other radicals, with the product stability apparently directly related to the stability of the substrate radical. For instance, nitric oxide and N F form a compound, difluoronitrosamine, only at low temperatures (3); at room temperature and atmospheric pressure the two radicals do not interact. Chlorine and N F react under the influence of ultraviolet light to produce chlorodifluoramine, C1NF (13). The equilibrium reaction is favored by high concentrations of chlorine and by high temperature (80° C). Be cause of this unfavorable equilibrium, the reaction of difluoramine and boron trichloride provides a more satisfactory route to chlorodifluoramine (11 ). Alkyl radicals also react with N F . Methyl- and ethyldifluoramine have been prepared by the irradiation of the corresponding iodides with ultraviolet light in the presence of N F (5). Similarly, thermal decomposition of azo compounds may be used as a source of alkyl radicals. 2
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2
2
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RI + N F
RNF + I
2
2
a-Difluoraminoisobutyronitrile (I) andterf-butyldifluoramine(II) have been pre pared from the corresponding azo compounds (13). Hexaphenylethane may be converted to trityldifluoramine with N F . These organodifluoramines show no tendency to dissociate to the parent radicals. 2
(CH ) C(CN)NF I 3
2
4
(CH ) CNF II
2
3
3
2
A new class of organic NF compounds, N-fluoroazoxy compounds, has re cently been reported. Trifluoronitrosomethane reacts with N F under the in fluence of light or heat to form N-fluoro-N'-trifluoromethyldiazine-N'-oxide (III) (6). A free radical mechanism for the reaction was proposed and it was sug 2
CF NO + N F 3
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4
ο Î CF N=NF + [F] III 3
gested that the reaction would be a general one. Considerable use of NMR spectroscopy was made to establish the structure of this unusual compound. Additional chemical evidence for the free radical character of N F is provided by the disclosure that it acts as an initiator in free radical chain reactions and may be used as a polymerization catalyst (I). 2
Table I.
H and F 1
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NMR Spectra of Nitrogen-Fluorine Compounds
(40 mc.) Compound NF (10) NF C1 ( 12) N F (4) H N F (9) Ο 3
2
2
4
2
F»(C./S.)* -8760 (triplet, J = 160 c./s.) - 8685 (broad) -5360 (broad) -2900 (doublet, J = 24 c./s.)
&(C./S.)
h
— +6 (triplet, J = 2Ac/s.) 2c./s.) 2c./s.) 2c./s.)
Ο CF N=NF 3
α 6
-4748 (broad)
Measured in cycles per second from trifluoroacetic acid standard. Measured in cycles per second from benzene standard. COLBURN; FREE RADICALS in Inorganic Chemistry Advances in Chemistry; American Chemical Society: Washington, DC, 1962.
130
ADVANCES IN CHEMISTRY SERIES
Chlorodifluoramine reacts with organomercurials to produce organodifluoramines (2). The mechanism of these reactions is obscure but may involve free radicals—for example, treatment of diethyl- or di-n-butylmercury with chlorodi fluoramine produces ethyl- and butyldifluoramine, respectively. These reactions were suggested by the reaction of NF C1 with mercury itself, which produces mercurous chloride and N F (12). The discovery of tetrafluorohydrazine and of its dissociation into difluoramino free radicals has opened a new area of both organic and inorganic chemistry. On the basis of the chemistry so far reported it may be assumed that a wide variety of fluoronitrogen compounds will soon be available for chemical investigation. Since nuclear magnetic resonance spectroscopy has proved to be an almost indispensable tool in these investigations, some of the data so far accumulated are summarized in Table I. 2
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Safety The known instability of haloamines should urge caution in investigations in this field. Reference should be made to the warnings contained in the original articles to avoid unnecessary trouble. Acknowledgment We are indebted to the Ordnance Corps of the Army for support for this work. Inspiration to work in the general area of fluoronitrogen chemistry was provided by Warren D . Niederhauser. Literature Cited (1) Cleaver, C . S., U . S. Patent 2,963,468 (Dec. 6, 1960). (2) Colburn, C . B., in "Advances in Fluorine Chemistry," by M . Stacey, J. C . Tatlow, and A . G . Sharpe, Vol. III, Butterworths, Washington, D . C . , 1962. (3) Colburn, C . B., Johnson, F . Α., Inorg. Chem., in press. (4) Colburn, C . B., Kennedy, Α., J. Am. Chem. Soc. 80, 5004 (1958). (5) Frazer, J. W . , J. Inorg. Nucl. Chem. 16, 23 (1960). (6) Frazer, J. W . , Holder, Β . E., Worden, E. F., Ibid., 24, 45 (1962). ( 7 ) Freeman, J. P., Kennedy, Α., Colburn, C . B., J. Am. Chem. Soc. 82, 5304 (1960). (8) Johnson, F . Α., Colburn, C . B., Ibid., 83, 3043 (1961). (9) Kennedy, Α., Colburn, C . B., Ibid., 81, 2906 (1959). (10) Muetterties, E. L., Phillips, W . D . , Ibid., 81, 1084 (1959). (11) Muller, N . , Lauterbur, P. C., Svatos, G . F . , Ibid., 79, 1807 (1957). (12) Petry, R. C . , Ibid., 82, 2400 (1960). (13) Petry, R. C . , Freeman, J. P., Ibid., 83, 3912 (1961). (14) Piette, L. H., Johnson, F . Α., Booman, Κ. Α., Colburn, C . B., J. Chem. Phys. 35, 1481 (1961). R E C E I V E D April 30, 1962.
COLBURN; FREE RADICALS in Inorganic Chemistry Advances in Chemistry; American Chemical Society: Washington, DC, 1962.
