H. J. Frohn - V. V. Bardin • Electrophilic Oxygenation with XeF2 - FbO in Hydrogen Fluoride
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however the nitrodeprotonation predominated [4],
Nevertheless, there is a partial similarity between
electrophilic oxygenation (formal primary step: hy-
droxyfluorination) and nitrofluorination of pentaflu-
orobenzenes CftF^X as shown by comparison of
data presented in Table III and Table IV. No simi-
larity between the two processes can be observed
in the case of oxygen-containing substituents X.
The main site of attachment of the nitro group to
C6F5X (X = OH, OCHF2 or OCftFs) is carbon C-4,
whereas the electrophilic oxygenation of C6F5OH
and C6F5OCH2CF3 proceeds predominantly at car-
bon atom C-l. These distinctions point out the dif-
ference of mechanisms of both electrophilic reac-
tions which require further investigations.
by l9F NMR spectrometry using C6H5CF3 as internal
quantitative reference for determination of product yields.
Products derived from [C6FsN M e3]+ salts were dissolved
in MeCN after evaporation of HF (Table I).
Reaction of bromopentafluorobenzene was also per-
formed by addition of XeF2 (92 mg, 0.544 mmol) to HF
(0.1 ml) which contained H2O (20 mg, 1.11 mmol) at -30
°C. followed by treatment with 11 (109 mg, 0.440 mmol)
in 0.1 ml HF at -30 °C. After shaking at r. t. for 15 min HF
was evaporated and the reaction products were dissolved
in dichloromethane. The l9F NMR spectrum showed the
resonances of 10, 11, 12 and 13 (molar ratio 5 : 1 : 1 : 1,
total yield 82 %).
The l9F NMR spectrum of the reaction mixture de-
rived from pentafluoroiodobenzene showed only the res-
onances of Ca F51F2(20) and CftF5IF4(21). Subsequent ex-
traction with dichlorom ethane and evaporation of HF led
to partial hydrolysis of pentafluorophenyliodinetetraflu-
oride to pentafluorophenyliodineoxydifluoride (22) with
residual water (Table I).
Experimental
The |l,F NMR spectra were measured on a Bruker WP
80 SY spectrometer at 75.40 MHz and on a Varian EM
360 L spectrometer at 56.4 MHz (CöFö internal refer-
ences). The chemical shifts <5(F) were related to CFCI3
[6(F) (C&F(,) = -162.9 ppm)]. The 'H NMR spectra were
measured on a Varian EM 360 L spectrometer at 60.0
MHz. Although the l9F chemical shifts of dienones 2. 5,
6. 11, 12, 24, 25 (in CCI4) were reported previously (see
[4] and references cited there), only in few cases fluorine-
fluorine coupling constants were determined. Therefore,
the 6(F) and i(F,F) values of these compounds together
with those of new dienones 8, 9, 17, 18. 29 and 30 were
measured in CH2CI2 or HF (Table II).
Reaction of dienone 2 with XeFi and FF_0 in HF
Oxygenation of
2 derived from pentafluorophenol
(0.543 mmol), H2O (0.778 m m ol)and XeF2(0.592 mmol)
in HF (0.15 ml) with an additional amount of xenon di-
fluoride (0.461 mmol) gave 3 beside residual 2 and, pre-
sumably, perfluorodiepoxycyclohexanone (65, 24 and 11
mol %).
Reaction of pentafluorophenyldiazonium salt with XeF2
and H2O in HF
Pentafluoroaniline (70 mg, 0.383 mmol) was dissolved
in AHF (0.15 ml) and N aN 02 (34 mg, 0.493 mmol)
was added at -10 °C. Immediately a deep violet solu-
tion was formed in a total conversion of C6F5NH2 to
[C6F5N2]+ [F (H F )„ r. Addition of XeF2 (150 mg, 0.887
mmol) caused gas evolution at ambient temperature and
discoloration of the solution. The l9F NMR spectrum
showed that the [C aF .s^T cation was unchanged. Also no
changes were observed when NbFs (190 mg, 1.00 mmol)
was added and the reaction mixture kept for 4 d at r. t..
[C6F5NM e3]+ [OTf]~ [8] and C6F5OCH2CF3 [9] were
prepared according to the literature. [CftFsNM e,^ [PF6]~
was precipitated from aqueous [CftF.^NMe.^ [OTf]- by
60 % HPFf,, washed with water until neutral and dried in
a vacuum over P4O 10 at 120 °C for 4 h (yield 90%).
HF was freshly distilled from ca. 5% SbFs - HF solu-
tion using PTFE-FEP equipment. All experiments were
performed in FEP tubes.
Reactions of C^F^X with XeFj and HiO in HF (general
procedure)
Reaction ofpentafluoroanilinium hexafluoroniobate with
XeF2 and H20 in HF
Pentafluorobenzene derivatives CaFsX. H2O and HF
were dissolved in a FEP tube, cooled down to -10 °C,
and xenon difluoride was added in portions. After each
addition the reactor was kept at room temperature till
completion of xenon evolution. Finally the reaction mix-
ture was kept at 20 - 22 °C for 20 min and controlled by
l9F NMR. HF was evaporated, the residue was dissolved
in dichloromethane. dried with MgS04, and analysed
Pentafluoroaniline (100 mg, 0.546 mmol) was added to
the suspension of NbF_<s (160 mg. 0.851 mmol) in HF (0.2
ml) at 0 °C. A colourless solution of [CaFsNH^]"^ [NbFa]-
resulted which showed resonances at -146.6 (F-2.6),
- 147.4 (F-4) and -157.6 (F-3,5) ppm (19F NMR). Addition
of XeF2 (139 mg. 0.822 mmol) at -10 °C caused slow gas
Unauthenticated
Download Date | 3/23/19 4:46 AM
Frohn
