Perfluoro Alkyl Hypofluorites and Peroxides Revisited

Article abstract of DOI:10.1002/chem.201903620

A more convenient synthesis of the perfluoro alkyl hypofluorite (F₃C)₃COF as well as the hitherto unknown (C₂F₅)(F₃C)₂COF compound is reported. Both hypofluorites can be prepared by use of the corresponding tertiary alcohols R^FOH and elemental fluorine in the presence of CsF. An appropriate access to these highly reactive hypofluorites is crucial. The hypofluorites are then transferred into their corresponding perfluoro bisalkyl peroxides R^FOOR^F [R^F=(F₃C)₃C, (C₂F₅)(F₃C)₂C] by treatment with partially fluorinated silver wool. NMR, gas-phase infrared, and solid-state Raman spectra of the perfluoro bisalkyl peroxides are presented and their chemical properties are discussed.

Full text of DOI:10.1002/chem.201903620

A Journal of
Accepted Article
Title: Perfluoro Alkyl Hypofluorites and Peroxides Revisited
Authors: Sebastian Hasenstab-Riedel, Jan Hendrik Nissen, Thomas
Drews, Benjamin Schröder, Helmut Beckers, and Simon
Steinhauer
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To be cited as: Chem. Eur. J. 10.1002/chem.201903620
Link to VoR: http://dx.doi.org/10.1002/chem.201903620
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Perfluoro Alkyl Hypofluorites and Peroxides Revisited
Jan H. Nissen, Thomas Drews, Benjamin Schröder, Helmut Beckers, Simon Steinhauer, and
Sebastian Riedel*[a]
Abstract: A more convenient synthesis of the perfluoro alkyl
hypofluorite (F3C)3COF as well as the hitherto unknown
(C2F5)(F3C)2COF compound is reported. Both hypofluorites can
be prepared by use of the corresponding tertiary alcohols RFOH
and elemental fluorine in the presence of CsF. An appropriate
access to these highly reactive hypofluorites is crucial. The
hypofluorites are then transferred into their corresponding
F3COCF=CF2, which has become a valuable fluorinated
monomer for the industrial synthesis of perfluoroxy alkanes
(PFA).[16]
Hypofluorites are highly hazardous compounds, which
requires sophisticated handling and safety precautions. A high
reactivity and oxidation power is often paired with an intrinsic
instability which may lead to a rapid exothermic decomposition by
contact to organic impurities or metal surfaces.[17] Decomposition
of RFOF to yield the corresponding carbonyl compounds [Eq. (1)]
is highly exothermic with reaction enthalpiesHR of up to
–400 kJ mol–1 (see Supporting Information, Table S2.1]. The
susceptibility to hydrolysis of perfluorinated hypofluorites, RFOF,
to alcohols increases with increasing numbers of fluorinated
groups [Scheme (1)]. Trifluoromethyl hypofluorite, F3COF, is
thermally rather stable up to temperatures above 450 °C and
hydrolysis in aqueous solution is very slow.[1] The chemistry of
perfluoro alkyl hypofluorites has been recently reviewed.[17]
Scheme 1: Increasing tendency of hydrolysis of selected perfluoro alkyl
hypofluorites, RFOF.
perfluoro
bisalkyl
peroxides
RFOORF
[RF = (F3C)3C,
(C2F5)(F3C)2C] by treatment with partially fluorinated silver wool.
NMR, gas-phase infrared and solid-state Raman spectra of the
perfluoro bisalkyl peroxides are presented and their chemical
properties are discussed.
Introduction
Cady has described the synthesis of the first perfluoro alkyl
hypofluorite, trifluoromethyl hypofluorite, F3COF, by the AgF2
catalyzed direct fluorination of methanol in 1948.[1] Since then a
variety of perfluoro[2] as well as partially chlorinated (e. g.
Cl3CCF2OF)[2,3] and nitrogen (e. g. NF2CF2CF2OF)[4] or sulfur (e.
g. FSO2CF2CF2OF)[5] containing and later even hydrogen (e. g.
H3COF)[6] substituted alkyl hypofluorites ROF (1) have been
isolated and characterized. An alternative route to perfluoro alkyl
hypofluorites is the fluorination of perfluoro ketones in the
presence of metal fluorides, MF (M = K, Rb, Cs) [Eq. (1)], as
described in 1966 by Ruff and Lustig.[7] Moreover, the direct
fluorination (with 10% F2 in N2) of sodium trifluoroacetate,
F3CCO2Na,[8] or trifluoroacetic acid, F3CCO2H,[9] leads to
formation of hypofluorite compounds in a temperature dependent
ratio. These hypofluorites were used in the pioneering work of
Hesse[10] and Rozen[11] as electrophilic fluorination agents or as
etching gas[12] for semiconductors. The relatively low dissociation
energy of the O–F bond in F3COF (184.2 kJ mol–1)[13] facilitates
insertion of carbon monoxide[14] into the O–F bond to produce
fluoroformiates, F3COC(O)F, and the addition of F3COF to
(per)fluorinated olefins which yield (per)fluorinated bisalkyl ethers,
F3COR.[15] Further reactions of functionalized ethers like
F3COCFCl-CF2Cl may then be reduced to the vinylether,
We found that perfluoroalkyl hypofluorites RFOF are
excellent starting compounds for the synthesis of otherwise
difficult accessible perfluoro bisalkyl peroxides RFOORF (2),[18]
which are synthetically valuable sources of fluoroalkoxy radicals,
RFO•.[19] Until very recently[18] our knowledge about perfluoro
bisalkyl peroxides was very scarce and limited to the two
homologues bis(trifluoromethyl) peroxide, (F3CO)2 (2a)[20] and
bis(nonafluoro-tert-butyl) peroxide, [(F3C)3CO]2 (2b).[21] The
volatile and rather resistant peroxide 2a (bp. –37 °C) was reported
in 1933 by Swarts[22] and prepared in 1957 by Cady et al.[23] from
trifluormethyl hypofluorite and carbonyl difluoride, F2CO. One
decade later Anderson et al. detected peroxide 2b among other
products obtained by the reaction of chlorine trifluoride and
perfluoro tert-butyl alcohol, (F3C)3COH (3b), in a high-pressure
stainless-steal reactor.[21] Later also the low-temperature
photolysis (−40 °C) of perfluoro tert-butyl hypofluorite, (F3C)3COF
(1b), in the presence of tetrafluorohydrazine, N2F4, was described
to yield peroxide 2b.[19] The gas-phase molecular structure of 2a
was investigated by electron diffraction[20] while the solid-state
structure of 2b has only very recently been published.[18] The
chemistry of these perfluoroalkyl peroxides have only been
scarcely investigated in the past. Among them are reactions with
carbon-carbon double bonds of fluorinated olefins[24] and
thiophenes.[25] Furthermore, the closely related compound class
of fluoroformyl peroxides, RF–OO–C(O)F,[26] as well as
perflurodiacyl peroxides, RFC(O)–OO–C(O)RF have been
[a]
J. H. Nissen, T. Drews, B. Schröder, H. Beckers, S. Steinhauer,
Prof. S. Riedel
Fachbereich für Biologie, Chemie, Pharmazie, Institut für Chemie
und Biochemie – Anorganische Chemie, Freie Universität Berlin,
Fabeckstraße 34/36, 14195 Berlin (Germany)
E-mail: s.riedel@fu-berlin.de
Supporting information for this article is given via a link at the end of
the document.
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investigated and represent important intermediates in the
to 150 kJ mol–1. Nevertheless, these perfluoro alkyl hypofluorites
are kinetically stable in the gas-phase up to 110 °C.[2] Therefore,
we were able to provide APCI mass spectra of tert-butyl
hypofluorite 1b (see Supporting Information, Figure S1.2). The
predominant species in the negative mode is the alkoxide ion
[(F3C)3CO]– (m/z = 235), while the molecular ion peak at
m/z = 254 is not observed. Interestingly, the peak at m/z = 285
can be assigned to an adduct or insertion of a CF2-fragment to
the alkoxide ion [(F3C)3CO+CF2]–, which was previously observed
for an perfluorinated ether bearing the perfluoro-tert-butyl
group.[30] Only perfluoro tert-pentyl hypofluorite (1c), which is
stable in solution for several minutes, is found to decompose
readily at room temperature within seconds to yield selectively
(F3C)2CO and C2F6, as proved by their gas-phase IR spectra
[Eq. (3)].[31],[32]
industrial synthesis of fluorous polyether chains[27]
.
Here we report a modified synthesis of tertiary perfluoroalkyl
hypofluorites RFOF [RF = (F3C)3C 1b, RF = (C2F5)(F3C)2C 1c] from
the corresponding alcohols RFOH [RF = (F3C)3C 3b,
RF = (C2F5)(F3C)2C 3c] with elemental fluorine in the presence of
excess CsF. These hypofluorites 1 were then treated with
fluorinated silver wool to form the perfluoro bisalkyl peroxides
RFOORF [RF = (F3C)3C (2b), RF = (C2F5)(F3C)2C (2c)].
Results and Discussion
Perfluoroalkyl hypofluorites, RFOF (1), were obtained according
to Eq. (1) by treatment of the corresponding carbonyl compound
with elemental fluorine in a stainless steel reactor under the
presence of any alkali metal fluoride, MF. The mixture was initially
cooled to –196 °C, and then slowly heated to –78 °C.[17,28,29]
Because these mixtures are highly hazardous and may explode
spontaneously,[28] we first improved this synthesis to avoid any
possible local heat formation and pressure increase during the
reaction.
The number of perfluoroalkyl hypofluorites 1 obtainable by
this procedure can be further increased by using perfluoro
alkylalcohols 3 instead of the perfluoro carbonyl compounds
according to Eq. (2). First, the perfluoro alkylalcohols 3b,c are
added to an excess of caesium fluoride in a stainless steel reactor
and the mixture is thoroughly shaken at room temperature in order
to dissipate the reaction heat of the subsequent fluorination
reaction. It is assumed that the alcohol reacts with CsF to the
corresponding caesium alcoholate and CsHF2.[29] The reactor is
cooled to –78 °C again and elemental fluorine is added in small
portions via a stainless steel line until no fluorine is consumed
anymore and the pressure remains constant. Excess fluorine is
then removed from the reaction mixture at –196 °C and the
hypofluorites 1 thus formed are distilled out of the reactor and
purified by trap-to-trap distillation. For the hypofluorites
(F3C)3COF (1b) and (C2F5)(F3C)2COF (1c) the conversion is
quantitative.
Probably due to the lack of stability, hypofluorite 1c has not yet
been characterized.[10,33] We therefore present low-temperature
NMR as well as the gas-phase IR spectrum of this poorly known
compound. These spectra clearly confirm the presence of 1c. The
fully coupled 13C NMR spectrum (see Supporting Information,
Figure S1.3) shows two quartets at  = 118.5 ppm (C–CF3) and
 = 116.8 ppm (F3C–CF2), where the latter one partly overlaps
with the CF2-triplet at  = 109.8 ppm. The chemical shift of the
quaternary carbon atom appears at  = 87.7 ppm. The first order
19F NMR spectrum of hypofluorite 1c (Figure 1) shows a doublet
of septets for the CF2 nuclei at  = –117.8 ppm, indicating a
4J(F,F) coupling to OF and to the two CF3 nuclei of 11.6 Hz. The
F3CCF2 signal at  = –81.9 ppm also shows a doublet of septets
with similar coupling constants of 5J(F,F) = 5.9 Hz to both, the OF
and the C–CF3 nuclei. The signal for the two CF3 groups occurs
as a doublet of triplet of quartets (d t q) at  = –68.3 ppm with a
4
large J coupling constant of 17.7 Hz to the OF nucleus, which
3
resonates at  = 150.8 ppm (t sept q). The J coupling constant
between the fluorine atoms of the pentafluoroethyl group is
smaller than 0.5 Hz.
This fluorination procedure was finally also used for the
synthesis of the known hypofluorites F3COF (1a), CF3CF2OF (1d)
and (F3C)2CFOF (1e) starting from the perfluoro carbonyl
compounds F2CO, F3CC(O)F and (F3C)2CO, respectively,
according to Eq. (1). Their IR and NMR spectra match those
previously reported.[2] Quantum-chemical calculations indicate
that apart from 1a all these perfluoro alkyl hypofluorites are
thermodynamically unstable by up to –400 kJ mol–1 in terms of
elimination of CF4 and formation of the corresponding carbonyl
compounds (see Supporting Information, Table S2.1). As
expected, elimination of elemental fluorine is endothermic by 120
Figure 1. 19F NMR spectrum of (C2F5)(F3C)2COF (3c) (376.88 MHz, external
[D6]Acetone, –60°C).
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Table 1. Gas-phase vibrational frequencies 푣̃ [cm–1] and relative IR band
intensities[a] compared to computed values for different rotational
conformers of (C2F5)(F3C)2COF (1c) at the B3LYP/aug-cc-pVTZ level of
theory.[b]
experiment
DFT
assignment
t-1
g-1
1342 (m)
1291 (s,sh)
1276 (vs)
1262 (vs)
1255 (vs)
1251 (vs)
1232 (s)
1181 (m)
1161 (w, sh)
1107 (m), 1078 (w)
1038 (vw)
1003 (m), 977 (w)
925 (w), 913 (w)
895 (m), 878 (m)
766 (vw)
743 (m)
730 (m)
613 (vw)
558 (sh)
1290 (75)
1273 (272)
1248 (606)
1239 (403)
1233 (58)
1218 (110)
1197 (297)
1161 (25)
1154 (63)
1064 (121)
1055 (12)
972 (100)
995 (25)
888 (117)
766 (5)
1308 (22)
1260 (421)
1246 (541)
1237 (338)
1221 (157)
1216 (240)
1201 (256)
1155 (5)
1153 (11)
1113 (14)
1047 (49)
963 (93)
967 (34)
898 (150)
765 (1)
(F2C–CF3)
(CF3)
(CF3)
(CF3)
(CF3)
(CF3)
(CF3)
(CF3)
(CF2)
(CO)
(C–CF2)

as(C–(CF3)2)
(OF)
(F2C–CF3)
(CF3)
(CF3)
(C(CF3)2)
(CC3)
(CF3)
(CF3)
(CF3)
739 (59)
725 (39)
619 (6)
537 (4)
525 (9)
740 (59)
725 (40)
621 (12)
537 (3)
527 (10)
499 (8)
Figure 2. Gas-phase IR spectrum of (C2F5)(F3C)2COF (3c) (bottom) and the
calculated spectrum for the most stable t-1 conformer (see Figure 3) at the
B3LYP/aug-cc-pVTZ level of theory (top trace).
539 (vw)
513 (vw)
484 (vw)
501 (7)
444 (2)
445 (3)
(C2F5)
The IR spectrum of hypofluorite 1c in the gas-phase is
compared to a computed IR spectrum at the DFT-B3LYP/aug-cc-
pVTZ level of theory in Figure 2. The experimental bands in the
mid-IR from 1107 to 878 cm–1 are split into two components,
probably due to the presence of at least two rotational conformers
in the gas-phase. Indeed, the DFT calculations revealed slightly
different IR spectra for the different trans and gauche rotational
conformers of 1c (Figure 3, Table 1 and the SI) and a global
minimum for the t-1 structure. This result agrees well with the
experimental IR spectrum, which shows strong absorption for the
C–F stretching modes in the region from 1291 to 1232 cm–1 and
the characteristic deformation bands of the CF3-groups at 766,
743, and 730 cm–1. Furthermore, the bands at 1107 and
1078 cm–1 are tentatively assigned to C–O stretching modes of
different rotamers of 1c. According to the calculations the O–F
stretching mode has a relatively low intensity and its position
varies up to 43 cm–1 depending on the conformer of 1c (see
Table 1 and SI). It can tentatively be assigned in the experimental
gas-phase IR spectrum to weak absorptions at 925 and
913 cm–1, but we cannot exclude that this band is superimposed
by the asymmetric stretching mode of the C–(CF3)2 fragment
located at 1003 cm–1. The bands at 895 and 878 cm–1 represent
C–C stretching modes of the pentafluoroethyl group of 1c. The
calculated position of this band varies for the different conformers
by 36 cm–1. The weak band at 613 cm–1 can be associated with
the CC3 deformation, while weaker deformation modes of the CF3-
group are found at 539 and 513 cm–1. A very weak absorption at
484 cm–1 fits well to a computed deformation mode of the C2F5-
group.
[a] Relative intensities in parentheses: vw = very weak, w = weak,
m = medium, s = strong, vs = very strong, sh = shoulder.
[b] For the different trans and gauche rotational conformers see Figure 3 and
Figures S2.
The hypofluorites 1b and 1c are converted in rather good
yield up to <70% into the corresponding symmetric perfluoro bis-
alkyl peroxides 2b and 2c, respectively, by using partially
fluorinated silver wool [see Exp. Details and Eq. (4)]. This reaction
does not proceed at low temperatures of –78 °C, while at 0 °C
mainly decomposition products of the hypofluorites are formed
[1b: CF4, (F3C)2CO; 1c: C2F6, (F3C)2CO].[31,32,34] When the
reaction vessel is held at temperatures of –50 to –45 °C for 48 to
72 h, peroxide 2b is obtained from 1b and separated by trap-to-
trap distillation in a –78 °C trap from the more volatile side
products CF4 and (F3C)2CO in an overall yield of >70%. Pure
peroxide 2b is rather stable at ambient temperature and
decomposes at temperatures above 100 °C to yield (F3C)2CO and
C2F6 with an activation energy of 148.7 ± 4.4 kJ mol–1.[35] Similarly,
hypofluorite 1c reacts to the peroxide 2c and it was purified from
the volatile side products C2F6 and (F3C)2CO by trap-to-trap
distillation, where it remains in a –78 °C trap in a yield of up to
66%.
However, attempts to convert the hypofluorites CF3CF2OF
(1d) and (F3C)2CFOF (1e) with fluorinated silver wool under
similar conditions to the corresponding perfluoro bisalkyl
peroxides failed and led solely to decomposition products (1d:
CF4,[34] F2CO,[36] 1e: CF4,[34] F3CC(O)F[37]) which were identified
by IR spectroscopy. The composition of the fluorinated silver wool
used in the synthesis of the peroxides 2b and 2c according to
Eq. (4) prepared as described in the experimental details was
E [kJ mol–1]:
0.0
1.3
8.4
3.2
Figure 3. Relative energies of trans and gauche conformers of (C2F5)(F3C)2COF
(1c) obtained at the B3LYP/aug-cc-pVTZ level of theory (fluorine atoms bound
to carbon are not shown).
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investigated by a powder X-ray diffraction analysis. It consists
mainly of silver(I) fluoride, AgF, but contains also some silver
subfluoride, Ag2F, silver(II) fluoride, AgF2, and elemental silver,
Ag (see Figure S1.1). However, attempts to reproduce the above
described conversion of hypofluorites 1 to peroxides 2 by using
either elemental Ag or commercial AgF instead of the fluorinated
silver wool failed and only decomposition products of the
hypofluorites were obtained.
constants of 290 Hz and 35 Hz, respectivly, show the expected
signals for the fluorine substituded carbon atoms at 118.5, 116.7
and 115.2 ppm and the resonance of the quaternary carbon atom
at 85.6 ppm slightly shifted to lower field compared to the
corresponding hypofluorite 1c. Three signals observed in the
19F NMR spectrum (Figure S1.8) are also shifted by Δ = 2 ppm
to lower field compared to the spectrum of the reactant 1c. This
consistent low field shift of the NMR signals underlines the strong
electron withdrawing effect of the perfluorinated tert-pentyl group
of peroxide 2c.
The mechanism of this solid-gas reaction for the formation
of peroxides from hypofluorites is still unknown and further studies
are necessary to explore this reaction. Powder diffraction
measurements of the fluorinated silver wool prior and after several
batches (Figure S1.1) indicates an increase of silver(I) fluoride at
the expense of silver(0) or silver subfluorides within several
reactions. From this result it can be assumed that the active site
of the partially fluorinated silver wool consists of an incompletely
coordinated silver subfluoride or silver(0) species which acts as a
fluorine-atom acceptor. We noticed that the fluorine-atom
acceptor ability of this species depletes, and thus, the yield of
peroxide formation decreases after several successful batches,
very likely due to fluorination of the active silver species and
formation of inactive silver(I) fluoride. Based on this assumption,
the following reaction mechanism can thus be postulated for the
solid-gas reaction: First, the active silver site may undergo an
oxidative addition of RFOF to form an alkoxide silver(II) inter-
mediate, which then decomposes into alkoxyl radicals, RFO•, and
silver(I) fluoride [Eq. (5)]. The free or loosely bound RFO• radicals
may then combine to form the peroxides (2).
B3LYP/aug-cc-pVTZ
x2
x2
experiment
2000 1800 1600 1400 1200 1000
wavenumber [cm1
800
600
400
]
Figure 4. Gas-phase IR spectrum of [(F3C)3CO]2 (2b) (bottom) in comparison
to a computed spectrum at the B3LYP/aug-cc-pVTZ level (top trace).
There are precedents for the formation of silver (II) alkoxides
and their decomposition into alkoxyl radicals. Wechsberg
previously described the reaction of AgF2 with F2CO and fluorine
and assumed the formation of an Ag(II)(ORF)2 intermediate.[38]
Owing to the high oxidation potential of Ag(II) (electron affinity:
21.45 eV),[39] the proposed Ag(II) alkoxide intermediates are
prone to a ligand-to-metal electron-transfer (LMCT) and even to
the formation of alkoxyl radical intermediates like
Ag(I)(O•RF)(ORF).[39] A similar radical mechanism has been
proposed for the AgF2 catalyzed low temperature reaction of F2
with SO3 to yield peroxy disulfuryl difluoride, (FSO2O)2.[40]
The 13C {19F} DEPTQ NMR spectrum[41] of neat [(F3C)3CO]2
(2b) shows two signals at  = 118.8 and 84.3 ppm associated with
the CF3 and the quaternary carbon nuclei. The 19F NMR spectrum
shows a singlet at  = –69.6 ppm (lit.:[42] –70.0 ppm) while the
resonance in the 17O NMR spectrum occurred in the characteristic
Figure 5. Gas-phase IR spectrum of [(C2F5)(F3C)2CO]2 (2c) (bottom) in
comparison to a computed spectrum at the B3LYP/aug-cc-pVTZ level (top
trace).
The IR spectrum of [(F3C)3CO]2 (2b) in the gas phase is
shown in Figure 4 together with the computed spectrum at the
DFT-B3LYP/aug-cc-pVTZ level of theory. The strongest
absorptions are associated with the CF3 stretching bands in the
region around 1300 cm–1 (Table S1.1). The sharp IR band at
1110 cm–1 is assigned to a C–O stretching mode while the second
C–O stretch appears at 1129 cm–1 in the low temperature Raman
spectrum (Figure S1.9). The characteristic C–C3 stretching bands
region of
a
peroxide compound[43] at  = 246 ppm, see
Figure S1.4. The oxygen atoms of (F3CO)2 (2a) resonate at
262 ppm in the 17O NMR spectrum (Figure S1.5). The base peak
in the APCI– mass spectrum of 2b (Figure S1.6) at 235 m/z
represents the [(F3C)3CO]– fragment. Also the [(F3C)3C]– fragment
can be assigned at 219 m/z, while the molecular ion peak at
470 m/z is not present. The 13C {19F} DEPTQ NMR spectra of
[(C2F5)(F3C)2CO]2 (2c) (Figure S1.7) with optimized 1J coupling
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of the tert-butyl group are found at 1002 and 982 cm–1 in the IR.
That agrees well with their computed band positions at the DFT-
B3LYP/aug-cc-pVTZ level of theory at 994 and 970 cm–1,
respectively. The corresponding Raman band shows a strong
absorption at 1027 cm–1.The calculated O–O stretching mode at
902 cm–1 can clearly be assigned to a Raman band at 865 cm–1.
Very strong Raman bands are also found for the symmetric CF3
deformation modes at 783 and 749 cm–1. Their counterparts in the
gas-phase IR spectrum of peroxide 2b appear at 739 and
731 cm–1. The asymmetric CF3 deformation modes are located at
541 and 496 cm–1 in the IR spectrum and at 569, 541 and
523 cm–1 in the Raman spectrum. A characteristic deformation of
the C–O–O–C peroxide moiety is assigned to a Raman band at
356 cm–1, close to the CF3 rocking modes in the region from 339
to 296 cm–1. Two strong Raman bands at 241 and 123 cm–1
represent CC3 deformation modes of [(F3C)3CO]2 (2b).
Figure 5 shows the IR spectrum of [(C2F5)(F3C)2CO]2 (2c)
together with the computed spectrum at the DFT-B3LYP/aug-cc-
pVTZ level of theory. As expected, it is very similar to the
spectrum of 2b and to that of its precursor 1c. The IR spectrum
shows in addition to the strong CF3 stretching modes in the region
from 1277 to 1229 cm–1 the characteristic C–C stretching mode of
the C2F5 group at 1340 cm–1. Weak and broad bands at 1187 and
1177 cm–1 in the IR and the Raman spectrum (Figure S1.10),
respectively, are assigned to stretching modes of the CF2-group,
and a strong IR absorption at 1105 cm–1 to the out-of-phase C–O
stretching mode. The in-phase C–O and C–CF2 stretching modes
of 2c are found in the Raman spectrum at 1132 and 1082 cm–1,
respectively. The corresponding out-of-phase C–CF2 stretching
mode appeared in the IR spectrum at 1086 cm–1. Weak to
medium intensity bands around 1000 cm–1 in both, the IR and
Raman spectra, are due to CC3 stretching modes and a strong
antisymmetric CF2 stretching mode is found in the IR Spectrum at
898 cm–1 (calc.: 929 cm–1). The Raman active O–O stretching
mode appears at 853 cm–1, in excellent agreement with the
calculation at 852 cm–1, and also the C–O–O–C deformation of
the peroxide, located at 352 cm–1 in the Raman spectrum is very
close to that of 2b (356 cm–1).
a ferrocenium cation. Indeed, the IR spectrum of the solid
(Figure S1.11) shows the characteristic vibration modes of the
ferrocenium cation.[44] For example, the weak v(CH) mode is
blueshifted by 36 cm–1 to 3121 cm–1 with respect to ferrocene and
the v(CC) mode assigned at 1421 cm–1 is also hypsochromically
shifted by 14 cm–1 in comparison to the reactant ferrocene. The
bands at 965, 724 and 536 cm–1 as well as strong absorption
bands in the region from 1300 to 1100 cm–1 are characteristic for
the anion, [OC(CF3)3]–.[45] Additionally, the APCI mass spectra
(Figure S1.12) show a peak at 235 m/z in the negative mode,
characteristic for the [OC(CF3)3]– alkoxide anion. In the positive
mode an analogous decomposition pathway, compared to that of
ferrocene, is observed. These spectra confirm the formation of
[FeCp2][OC(CF3)3].
To a sample of [(F3C)3CO]2 (2b) elemental fluorine was
added to a total pressure of about 1 bar at r.t. in a PFA tube. The
tube was then flame-sealed at liquid nitrogen temperatures and
after reaching r.t. NMR spectra were recorded (see the
Supporting Information, Figure S1.13). The elemental fluorine is
detected at a chemical shift of  = 425 ppm (liquid: 422±1 ppm,
gaseous 419±1 ppm)[46]. Peroxide 2b resists elemental fluorine,
and its solubility in 2b is consistent with the low dipole moment as
indicated by the dihedral angle  of the peroxide unit of 180° in
the solid state and the perfluorinated nature of this compound.[18]
The longitudinal relaxation time T1 of the dissolved F2 was
determined by an inversion recovery experiment to be
T1 = 13.5 ms (Figure S1.13). This is approximately 300 times
larger than T1 for gaseous fluorine of 0.045 ms in the pressure
range from 1 to 2 bar.[47] This indicates that the fast relaxation due
to the spin-rotation mechanism observed for gaseous fluorine is
hindered and proofs that the fluorine is indeed dissolved in
peroxide 2b.
Conclusions
We present a convenient synthesis to highly reactive perfluoro
alkyl hypofluorite compounds RFOF from the corresponding
alcohol and fluorine with excess CsF. Spectroscopic analysis of
the hitherto undescribed (C2F5)(F3C)2COF with support of
quantum-chemical calculations are reported. We provide a new
synthetic approach for perfluoro bisalkyl peroxides RFOORF by
the reaction of hypofluorites with fluorinated silver wool.
Furthermore, we also show the inertness of [(F3C)3CO]2 towards
strong oxidizers such as elemental fluorine. The liquid
temperature range from 16 to 99 °C for the unpolar peroxide 2b
together with its inertness towards strong oxidizing halogens
demonstrates its potential as a solvent for oxidation and
halogenation reactions. By irradiation with UV light perfluoro alkyl
peroxides 2 can be activated to generate valuable RFO• radicals
for synthetic applications such as perfluoro alkoxy group transfer
reagents.
A full list of all experimental and computed wavenumbers together
with a tentative assignment is given in the Supporting Information,
Table S1.2.
In previous studies, the synthetically valuable fluorinated
radicals F3CO• or (F3C)3CO• were generated by photolysis of the
corresponding peroxide (F3CO)2 (2a) or [(F3C)3CO]2 (2b),
respectively.[19] The recently recorded gas-phase UV/Vis spectra
of the perfluorinated bisalkyl peroxides (RFO)2 (RF = F3C (2a),
(F3C)3C (2b) and (C2F5)(CF3)2C (2c)) show that for 2a the lowest
UV transition is below 200 nm, while the bulkier substituted
peroxides 2b,c exhibit weaker red-shifted transitions at 253 and
250 nm, respectively.[18]
As descriebed ealier, ferrocene, FeIICp2, is oxidized to
ferrocenium, [FeIIICp2]+, by addition of peroxide 2b [Eq. (6)].[18] An
immediate color change of the solid from orange to dark green is
observed during the reaction, which is typical for the formation of
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10.1002/chem.201903620
Chemistry - A European Journal
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[5] W. Storzer, D. D. Desmarteau, Inorg. Chem. 1991, 30, 4122-
4125.
Experimental Section
[6] a) M. Kol, S. Rozen, E. Appelman, J. Am. Chem. Soc. 1991,
113, 2648-2651; b) E. H. Appelman, D. French, E. Mishani, S.
Rozen, J. Am. Chem. Soc. 1993, 115, 1379-1382.
[7] J. K. Ruff, A. R. Pitochelli, M. Lustig, J. Am. Chem. Soc. 1966,
88, 4531-4532.
[8] G. K. Mulholland, R. E. Ehrenkaufer, J. Org. Chem. 1986, 51,
1482-1489.
[9] A. Sekiya, D. D. Desmarteau, Inorg. Chem. 1980, 19, 1328-
Experiments were carried out at strictly dry and oxygen free conditions in
glass tubes using Teflon® valves or in stainless steel vessels. Purchased
starting material was used without further purification. NMR spectra of neat
liquid substances were recorded on a JEOL 400 MHz ECS or ECZ
spectrometer using a capillary filled with [D6]Acetone (1H NMR: 2.05 ppm,
400.53 MHz; 13C NMR: 29.8 ppm, 100.51 MHz) and CFCl3 19F NMR:
(
0 ppm, 376.13 MHz) as external standards. The chemical shift and scalar
coupling constants were obtained by the program Mestrenova 10.0.[48]
Raman spectra were measured at liquid nitrogen temperature on a Bruker
MultiRAM II spectrometer equipped with a 1064 nm CW DPSS laser and
a LN2 cooled germanium detector at a resolution of 4 cm−1. Gas-phase
infrared spectra were recorded using a Bruker Vector 22 spectrometer at
a resolution of 2 cm−1. UV/Vis-spectra of gaseous samples were obtained
using a Perkin-Elmer Lambda-900 spectrophotometer. Mass spectra were
measured with an Advion expressionL compact mass spectrometer. The
m/z values of the monisotopic peaks are given. The NMR relaxation time
T1 was determined by the 180°--90° pulse sequence technique. Powder
diffraction data were collected on a STOE IPDS II/T instrument at 290 K
with Mo K radiation ( = 0.71073 Å) using a graphite monochromator.
Integration was performed with STOE X-Area V1.56, data analysis and
Rietveld refinement was performed with X'Pert HighScore Plus V2.2c.
1330.
[10] D. H. R. Barton, R. H. Hesse, M. M. Pechet, G. Tarzia, H. T.
Toh, N. D. Westcott, J. Chem. Soc., Chem. Commun. 1972, 0,
122-123.
[11] S. Rozen 1996, 1717-1736.
[12] T. Kashiwaba, H. Oomori, A. Yao, Dry Etching Agent, Dry
Etching Method and Method for Producing Semiconductor
Device, WO 2018/159368.
[13] R. C. Kennedy, J. B. Levy, J. Phys. Chem. 1972, 76, 3480-
3488.
[14] a) P. J. Aymonino, Chem. Commun. 1965, 241; b) L. Du, D. D.
Desmarteau, V. Tortelli, M. Galimberti, J. Fluorine Chem. 2009,
130, 830-835.
[15] K. K. Johri, D. D. DesMarteau, J. Org. Chem. 1983, 48, 242-
250.
[16] W. Navarrini, V. Tortelli, A. Russo, S. Corti, J. Fluorine Chem.
1999, 95, 27-39.
Safety note: Extreme caution should be exercised when working with
elemental fluorine and hypofluorites. Explosions have been reported[2,49]
handling these extremely hazardous compounds. Although the described
perfluoroalkyl peroxides were found to be insensitive to shock and
friction[18] according to the U. N. Recommendations on the Transport of
Dangerous goods,[50] we cannot exclude explosive reactions in mixtures
with other substances.
[17] V. Francesco, M. Sansotera, W. Navarrini, J. Fluorine Chem.
2013, 155, 2-20.
[18] J. H. Nissen, T. Stüker, T. Drews, S. Steinhauer, H. Beckers,
S. Riedel, Angew. Chem. Int. Ed. 2019, 58, 3584-3588;
Angew. Chem. 2019, 131, 3622-3626.
[19] M. S. Toy, R. S. Stringham, J. Fluorine Chem. 1976, 7, 375-
383.
[20] C. J. Marsden, L. S. Bartell, F. P. Diodati, J. Mol. Struct. 1977,
39, 253-262.
[21] D. E. Gould, C. T. Ratcliffe, L. R. Anderson, W. B. Fox, J.
Chem. Soc. D 1970, 216.
[22] F. Swarts, Bull. Soc. Chim. Belg. 1933, 102-113.
[23] R. S. Porter, G. H. Cady, J. Am. Chem. Soc. 1957, 79, 5628-
5631.
[24] H. L. Roberts, J. Chem. Soc. 1964, 4538-4540.
[25] W. J. Peláez, G. A. Argüello, Tetrahedron Letters 2010, 51,
5242-5245.
[26] S.-L. Yu, D. D. Desmarteau, Inorg. Chem. 1978, 17, 304-306.
[27] W. Navarrini, M. Sansotera, P. Metrangolo, P. Cavallotti, G.
Resnati, Modification of carbonaceous materials, WO
2009/019243 A1.
Acknowledgements
We gratefully acknowledge the Zentraleinrichtung für Daten-
verarbeitung (ZEDAT) of the Freie Universität Berlin for the
allocation of computer time. The authors thank the Graduate
School 1582 “Fluorine as a Key Element” (RTN 1582) as well as
the CRC 1349 “Fluorine-Specific Interactions: Fundamentals and
Function” (project number 387284271) for financial support. We
are grateful to the Solvay Fluor GmbH for providing starting
materials and for fruitful discussions and the expertise of Holger
Pernice.
[28] D. D. DesMarteau, Inorg. Chem. 1970, 9, 2179-2181.
[29] M. E. Redwood, C. J. Willis, Can. J. Chem. 1965, 43, 1893-
1898.
[30] M. S. Toy, R. S. Stringham, J. Fluorine Chem. 1975, 5, 25-30.
[31] I. M. Mills, W. B. Person, J. R. Scherer, B. Crawford, J. Chem.
Phys. 1958, 28, 851-853.
Conflict of Interest
[32] C. V. Berney, Spectrochim. Acta 1965, 21, 1809-1823.
[33] a) I. Mori, T. Tamura, M. Ohashi, Hypofluorite gas for removal
of deposits by solid-gas reaction in cleaning or etching, EP
924282; b) I. Mori, T. Kawashima, M. Ohashi, T. Tamura,
Method for stripping hyposulfites from flue gases in cleaning or
etching of semiconductor devices, JP 2001321638.
[34] Woltz, P. J. H., A. H. Nielsen, J. Chem. Phys. 1952, 20, 307-
312.
The authors do not declare any conflict of interest.
Keywords: gas-phase fluorine chemistry • hypofluorites •
perfluoro bisalkyl peroxides • vibrational spectroscopy
[1] K. B. Kellogg, G. H. Cady, J. Am. Chem. Soc. 1948, 70, 3986-
[35] R. Ireton, A. S. Gordon, D. C. Tardy, Int. J. Chem. Kinet. 1977,
3990.
9, 769-775.
[2] J. H. Prager, P. G. Thompson, J. Am. Chem. Soc. 1965, 87,
[36] M. J. Hopper, J. W. Russell, J. Overend, J. Chem. Phys. 1968,
48, 3765-3772.
[37] M. D. Hurley, T. J. Wallington, M. S. Javadi, O. J. Nielsen,
Chem. Phys. Lett. 2008, 450, 263-267.
[38] M. Wechsberg, G. H. Cady, J. Am. Chem. Soc. 1969, 91,
4432-4436.
230-238.
[3] P. G. Thompson, J. H. Prager, Fluoroxy Compounds,
US3442927A.
[4] M. Lustig, A. R. Pitochelli, J. K. Ruff, J. Am. Chem. Soc. 1967,
89, 2841-2843.
This article is protected by copyright. All rights reserved.

10.1002/chem.201903620
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FULL PAPER
[39] W. Grochala, Z. Mazej, Phil. Trans. R. Soc. A 2015, 373.
[40] F. B. Dudley, G. H. Cady, J. Am. Chem. Soc. 1957, 79, 513-
514.
[41] R. Burger, P. Bigler, J. Magn. Reson. 1998, 135, 529-534.
[42] N. S. Walker, D. D. Desmarteau, J. Fluorine Chem. 1975, 5,
135-139.
[43] J.-P. Kintzinger, H. Marsmann, Oxygen-17 and Silicon-29,
Springer Berlin Heidelberg, Berlin, Heidelberg, 1981.
[44] I. Pavlík, J. Klikorka, Coll. Czech. Chem. Comm. 1965, 30,
664-674.
[45] A. Reisinger, N. Trapp, I. Krossing, Organometallics 2007, 26,
2096-2105.
[46] J. W. Nebgen, W. B. Rose, F. I. Metz, J. Mol. Spectrosc. 1966,
20, 72-74.
[47] V. R. Celinski, M. Ditter, F. Kraus, F. Fujara, J. Schmedt auf
der Günne, Chemistry 2016, 22, 18388-18393.
[48] C. Cobas, S. Domínguez, N. Larin, I. Iglesias, C. Geada, F.
Seoane, M. Sordo, P. Monje, S. Fraga, R. Cobas et al.,
MestReNova, Mestrelab Research S.L., 2015.
[49] C. Lu, J.-H. Kim, D. D. Desmarteau, J. Fluorine Chem. 2010,
131, 17-20.
[50] Recommendations on the transport of dangerous goods.
Model regulations, UNITED NATIONS, New York, 2007.
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FULL PAPER
Once Upon a Time… Hypofluorites
J. H. Nissen, T. Drews, B. Schröder, H.
Beckers, S. Steinhauer, Prof. S. Riedel*
The convenient synthesis of alkyl
hypofluorites RFOF [RF = (F3C)3C,
(C2F5)(F3C)2C] is the germ cell for
Page No. – Page No.
Perfluoro Alkyl Hypofluorites and
Peroxides Revisited
perfluoro
bisalkyl
peroxides.
Hypofluorites are prepared from the
corresponding alcohols RFOH and
elemental fluorine. The perfluoro bis-
tert-butyl peroxide is highly inert
towards oxidizers and even dissolves
elemental
fluorine
without
decomposition.
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