UDC 547.412.722.7:547.433.27

CHEMISTRY

B. L. Dyatkin, R. A. Bekker, Yu. S. Konstantinov,
Academician I. L. Knunyants

ON THE ADDITION OF NITROSYL FLUORIDE AND NITROSYL CHLORIDE TO ALKYL PERFLUOROVINYL ETHERS

Comparatively few examples are known of the interaction of nitrosyl fluoride with organic compounds. In 1908 Ruff et al. \(^{(1)}\) obtained nitrobenzene by the action of FNO on benzene. Recently, reactions of FNO with fluoroolefins \(^{(2-4)}\), perfluoroketones \(^{(5)}\), and perfluoroazaalkenes \(^{(4)}\) have been studied. The reaction with fluoroolefins is of particular interest as a possible route to the synthesis of perfluoronitrosoalkanes. However, only the addition of nitrosyl fluoride to perfluoroisobutylene smoothly gives tert-nitrosoperfluoroisobutane \((\mathrm{CF_3})_3\mathrm{CNO}\); in all other cases the initially formed nitroso compounds undergo further transformations. It is interesting to note that nitrosyl fluoride reacts very readily with hydrogen-containing fluoroolefins—vinylidene fluoride \(\mathrm{CF_2{=}CH_2}\) and trifluoroethylene \(\mathrm{CF_2{=}CFH}\). Fully fluorinated olefins—tetrafluoroethylene \(\mathrm{CF_2{=}CF_2}\) and hexafluoropropylene \(\mathrm{CF_2{=}CFCF_3}\)—react under rather severe conditions \((100—150^\circ)\), whereas addition of nitrosyl fluoride to perfluoroisobutylene \(\mathrm{CF_2{=}C(CF_3)_2}\) already occurs at \(20^\circ\). Such a change in reactivity in the series of fluoroolefins can be explained only by the fact that, on passing from vinylidene fluoride to perfluoroisobutylene, accompanied by accumulation of electronegative substituents at the double bond and a decrease in its electron density, the reaction mechanism changes: with respect to the first members of the series nitrosyl fluoride is an electrophilic reagent, whereas with respect to perfluoroisobutylene it is a nucleophilic reagent (cf. \(^{(4)}\)):

\[ \mathrm{CF_2{=}CH_2} \ \xrightarrow{\mathrm{NO^+}}\ \left[\overline{\mathrm{CF_2{-}CH_2NO}}\right] \ \xrightarrow{\mathrm{F^-}}\ \mathrm{CF_3CH_2NO} \to \text{etc.} \]

\[ \begin{array}{c} \mathrm{CF_3}\\[-2pt] \backslash\\[-2pt] \mathrm{C{=}CF_2}\\[-2pt] /\\[-2pt] \mathrm{CF_3} \end{array} \ \xrightarrow{\mathrm{F^-}}\ \left[ \begin{array}{c} \mathrm{CF_3}\\[-2pt] \backslash\\[-2pt] \mathrm{C^-{-}CF_3}\\[-2pt] /\\[-2pt] \mathrm{CF_3} \end{array} \right] \ \xrightarrow{\mathrm{NO^+}}\ \begin{array}{c} \mathrm{CF_3}\\[-2pt] \backslash\\[-2pt] \mathrm{CF_3{-}C{-}NO}\\[-2pt] /\\[-2pt] \mathrm{CF_3} \end{array} \]

Addition of nitrosyl chloride to olefins proceeds, as a rule, by an ionic electrophilic mechanism \(^{(6)}\): the reaction rate increases with increasing electron density of the double bond, and the orientation corresponds to the polarization of the reagents:

\[ \begin{array}{c} \mathrm{CH_3}\\[-2pt] \backslash\\[-2pt] \mathrm{C{=}CH_2}\\[-2pt] /\\[-2pt] \mathrm{CH_3} \end{array} \ \xrightarrow{\mathrm{NO^+}}\ \left[ \begin{array}{c} \overline{\mathrm{CH_3}}\\[-2pt] \backslash\\[-2pt] \mathrm{C^+{-}CH_2NO}\\[-2pt] /\\[-2pt] \mathrm{CH_3} \end{array} \right] \ \xrightarrow{\mathrm{Cl^-}}\ \left[ \begin{array}{c} \overline{\mathrm{CH_3}}\\[-2pt] \backslash\\[-2pt] \mathrm{CCl{-}CH_2NO}\\[-2pt] /\\[-2pt] \mathrm{CH_3} \end{array} \right]_2 \]

Nitrosyl chloride reacts especially readily with simple vinyl ethers \(^{(7)}\).

Fluoro derivatives of ethylene, whose double-bond electron density is lowered in comparison with ordinary olefins, nevertheless retain the ability to add nitrosyl chloride by the ionic mechanism, with formation of 1,2-nitrosochlorides, which under the reaction conditions are oxidized to nitro compounds \((^{8})\). For fluoroolefins, addition of nitrosyl chloride by a radical mechanism is also known, as a result of which chloronitrosoalkanes can be obtained \((^{9,10})\). The possibility of homolytic addition of nitrosyl fluoride seems doubtful (at least for the cases described), since the F—N bond in F—N=O is much stronger than the Cl—N bond in Cl—N=O (55.4 and 38.0 kcal/mole, respectively \((^{11})\)).

Table 1

Chemical shifts in the \(^{19}\mathrm{F}\) NMR spectra, measured relative to \(\mathrm{CF_2Cl_2}\)

In connection with the question of the mechanism of addition of nitrosyl halides, especially FNO, to fluorinated unsaturated compounds, essential data, as we believed, could be obtained by studying their reactions with such fluoroolefins in which the presence of strong electron-donor substituents gives the multiple bond an evidently nucleophilic character and imparts to it a distinct polarization. This reaction was therefore studied by us using as examples the interaction of FNO and ClNO with alkyl perfluorovinyl ethers—methyl trifluorovinyl ether \(\mathrm{CH_3OCF{=}CF_2}\) (I), ethyl trifluorovinyl ether \(\mathrm{C_2H_5OCF{=}CF_2}\) (II), methyl-\(\beta\)-chlorodifluorovinyl ether \(\mathrm{CH_3OCF{=}CFCl}\) (III), ethyl-\(\beta\)-chlorodifluorovinyl ether \(\mathrm{C_2H_5OCF{=}CFCl}\) (IV), methyl perfluoropropenyl ether \(\mathrm{CH_3OCF{=}CFCF_3}\) (V), ethyl perfluoropropenyl ether \(\mathrm{C_2H_5OCF{=}CFCF_3}\) (VI), and ethyl perfluoroisobutenyl ether \(\mathrm{C_2H_5OCF{=}C(CF_3)_2}\) (VII). It turned out that vinyl ethers I—VI react with FNO and ClNO exceptionally readily—at \(-78^\circ\) and practically instantaneously, with formation of monomeric nitroso compounds, as could be judged from the intense blue color of the reaction mixture. Ether VII is considerably less active: at \(-78^\circ\) it does not react with FNO or ClNO, and at room temperature it adds only FNO; no reaction with ClNO is observed.

The nitroso compounds obtained as a result of the interaction of nitrosyl fluoride and chloride with alkyl perfluorovinyl ethers are relatively stable and, at reduced temperature (\(-10 \div -15^\circ\)), can be stored for a fairly long time. The maximum absorption frequency of the nitroso group in the IR spectrum is \(1595\ \mathrm{cm^{-1}}\). The \(^{19}\mathrm{F}\) NMR spectra indicate that the order of addition corresponds to the polarization of the reagents—the nitroso group is directed toward the relatively negative atom, and the halogen toward the relatively positive carbon atom of the double bond (see Table 1). Thus, the totality of the data obtained indicates that the interaction of FNO and ClNO with vinyl ethers

—proceeds as an electrophilic addition reaction.

\[ \mathrm{ R{-}CF{=}CF{-}O{-}R' \ \xrightarrow{NO^+}\ [R{-}CF{-}\overset{+}{CF}{-}O{-}R'] \ \xrightarrow{X^-}\ R{-}CF{-}CF{-}O{-}R' } \]
\[ \mathrm{ \phantom{R{-}}| \qquad \phantom{CF{-}}| \qquad\qquad\quad | \quad | } \]
\[ \mathrm{ \phantom{R{-}}NO \qquad \phantom{CF{-}} \qquad\quad NO \quad X } \]

\[ \mathrm{R=F,\ Cl,\ CF_3;\quad R'=CH_3,\ C_2H_5;\quad X=F,\ Cl.} \]

As for ethyl perfluoroisobutenyl ether, its relative inertness is consistent with the electrophilic addition mechanism given above. However, one cannot exclude the possibility that addition of FNO to it occurs, as in the case of perfluoroisobutene, by a nucleophilic mechanism. In any case, it is of interest that nitrosyl fluoride adds, whereas nitrosyl chloride does not react under the conditions studied. This fact can be explained by the greater polarity of the nitrogen–halogen bond in nitrosyl fluoride. The reaction found makes accessible an extensive new class of fluorinated nitroso compounds—β-alkoxyperfluoronitrosoalkanes—which are of interest for comprehensive study. The synthesized nitroso compounds, their yields, constants, and analytical data are given in Table 2.

Table 2

β-Alkoxyperfluoronitrosoalkanes

* The yield was practically quantitative.

Experimental Part

Reaction of ethyl perfluoropropenyl ether (VI) with nitrosyl fluoride. To 8.9 g (0.05 mole) of VI at −78° and with periodic shaking, 3 ml (0.08 mole) of nitrosyl fluoride was gradually added. After 15 min after completion of the addition, the reaction mass was poured, with stirring, into ice water. The lower layer—an intensely blue liquid—was separated, dried with phosphorus anhydride, and distilled. The reactions of VI with nitrosyl chloride and of III–V with FNO and ClNO were carried out analogously.

Ethyl trifluorovinyl ether (II) and nitrosyl chloride. To a solution of 4.5 ml (0.1 mole) of nitrosyl chloride in 15 ml of Freon-12 \((\mathrm{CF_2Cl_2})\) at −78° and with periodic shaking, 11.7 g (0.09 mole) of II was slowly added. After 15 min, the solvent was distilled off on a column for low-temperature rectification; the residue was poured into ice water, and the nitroso ether was separated, dried with phosphorus anhydride, and distilled. The reactions of II with nitrosyl fluoride and of I with FNO and ClNO were carried out analogously. This change in the procedure in comparison with that described above (pri-

the change of solvent and the reverse order of mixing of the reagents) is caused by the ability of alkyl trifluorovinyl ethers to copolymerize with the nitroso compounds formed as a result of the addition of nitrosyl fluoride and nitrosyl chloride to them.

Addition of nitrosyl fluoride to ethyl perfluoroisobutenyl ether (VII). In a steel autoclave with a capacity of 50 ml, lined with Teflon, were placed 32.1 g (0.14 mole) of VII and 6 ml (0.16 mole) of nitrosyl fluoride. The autoclave was shaken at room temperature for 15 h, and the reaction mixture was then treated in the same way as in the other cases.

The purity of the nitroso ethers obtained was monitored by gas–liquid chromatography (adsorbent—diatomaceous brick; liquid phase—thiochol (20%); carrier gas—helium; thermal-conductivity detector).

Institute of Organoelement Compounds
Academy of Sciences of the USSR

Received
9 VII 1965

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