Decomposition of pentafluoroallyl fluorosulfate oxide

Article abstract of DOI:10.1134/S1070427209030197

Decomposition of pentafluoroallyl fluorosulfate oxide under nucleophilic catalysis is studied. The possible reaction mechanism is considered.

Full text of DOI:10.1134/S1070427209030197

ISSN 1070-4272, Russian Journal of Applied Chemistry, 2009, Vol. 82, No. 3, pp. 449–455. © Pleiades Publishing, Ltd., 2009.
Original Russian Text © N.V. Lebedev, V.V. Berenblit, P.E. Troichanskaya, V.A. Gubanov, 2009, published in Zhurnal Prikladnoi Khimii, 2009, Vol. 82,
No. 3, pp. 455–461.
ORGANIC SYNTHESIS AND INDUSTRIAL
ORGANIC CHEMISTRY
Decomposition of Pentafluoroallyl Fluorosulfate Oxide
N. V. Lebedev, V. V. Berenblit, P. E. Troichanskaya, and V. A. Gubanov
Lebedev Research Institute of Synthetic Rubber, Federal State Unitary Enterprise, St. Petersburg, Russia
Received November 11, 2008
Abstract—Decomposition of pentafluoroallyl fluorosulfate oxide under nucleophilic catalysis is studied. The
possible reaction mechanism is considered.
DOI: 10.1134/S1070427209030197
Decomposition of pentafluoroallyl fluorosulfate
oxide (AFSO) under the action of cesium and
potassium fluorides gives difluoromalonyl difluoride
(MDF) in high yield [1]. The synthesis of MDF
consists in addition of sulfur trioxide to hexafluoro-
propene (HFP) with the formation of pentafluoroallyl
fluorosulfate (AFS) [2, 3], its liquid-phase oxidation to
AFSO [4], and decomposition of AFSO under the
action of fluoride ions with simultaneous elimination
of sulfuryl fluoride:
O
O
[O]
SO2, BF3
CF2=CFCF3
HFP
CF2=CFCF2OSO2F
AFS
CF2−CFCF2OSO2F
CCF2C
MDF
−SO2F2
F
F
AFSO
A study of the third step of the MDF synthesis
showed that decomposition of AFSO under the action
of nucleophilic agents yields a multicomponent
mixture of products whose identification was not
considered in the literature. It was necessary to find the
conditions of AFSO decomposition (taking into
account the effect of the nucleophilic agent, solvent,
and temperature) that ensure the highest MDF yield
and to identify the by-products.
As seen from the structure, the AFSO molecule has
two electrophilic centers. Their attack by the fluoride
anion results in isomerization of the oxirane ring and
elimination of sulfuryl fluoride, with the formation of
MDF molecule containing two acyl fluoride groups:
F−
O
O
O
O
F−
−OCF2CF2OS
O
CF2−CFCF2OS−F
CCF2C
−SO2F2
−2F−
F
F
F
O
F−
It is known that in hexafluoropropene oxide
(HFPO) fluoride anion attacks the C2 atom which has
the higher positive charge density in the ring to form
perfluoropropionyl fluoride [5]. Our quantum-chemical
calculations (HyperCube 8.0.4 program, AM1
semiempirical method) revealed in AFSO and HFPO
molecules the centers that are preferentially accessible
to nucleophilic attack.
It follows from the charge density distribution that
the fluoride ion should primarily attack the sulfur atom
of the fluorosulfate group. Zapevalov [6] noted that the
449

450
LEBEDEV et al.
_
_
_
0.083
0.913
0.138
_
0.476
_
_
_
0.093
_
_
_
_
_
0.068
0.399
0.137
0.838
0.057
0.350
0.122
2.953
0.522
_
0.088
_
0.186
_
0.248
0.136
0.945
0.138
0.057
_
_
0.081
0.135
0.078
AFSO
HFPO
presence of an electrophilic fluorosulfate group in the
β-position to the epoxy ring facilitates the nucleophilic
attack of both functional groups, resulting in simulta-
neous ring opening and elimination of fluorosulfate in
the form of sulfuryl difluoride. However, in the case of
simultaneous attack of the fluoride anion, the
isomerization of the oxirane ring should result in
formation of trifluoropyruvyl fluoride rather than
MDF:
predominant occurrence of side oligomerization
processes (run no. 18). Potassium fluoride in the
presence of activators [dioxane, diglyme, tetraglyme,
ethylene glycol, PEG oligomers (M = 400–1500)] and
the complex Et3N·3HF in acetonitrile appeared to be
more effective nucleophilic agents from the viewpoint
of MDF formation. Addition of solvents capable of
specific solvation of cations in the KF–acetonitrile
system increased the MDF yield and decreased the
formation of by-products. Tertiary amines appeared to
be chemically unstable under the reaction conditions
(run nos. 11, 13) because of the reaction with the
fluorosulfate group in accordance with [7]. Addition of
onium salts led to an increase in the overall reaction
rate, but the amount of MDF in the reaction products
decreased and that of the oligomers increased (run
no. 17). In DMSO on KF, the reaction was accom-
panied by considerable oligomerization and tarring
(run no. 14). On KF without solvent and in nonpolar
aprotic solvents (toluene, benzene, hexane), there was
no reaction at all, which indicates that the catalytic
species is the dissolved fluoride (run nos. 1, 2, 12).
_
F
O
CFCF2OS
O
_
O
F
O
F
CF2
CF3CC
_
SO2F2
_
_
F
F
2
O
This assumption contradicts the experimental data,
as trifluoropyruvyl fluoride was not detected in AFSO
decomposition products.
The structure of AFSO suggests the possible
occurrence of a series of undesirable processes. In
particular, the reaction of intermediate alkoxides with
the epoxy group of AFSO may result in its
oligomerization with the formation of a series of
polyoxyalkyl sulfates. Furthermore, the fluorosulfate
group can be replaced by an alkoxy group with the
formation of another series of oligomers. Replacement
of fluorosulfate groups by fluoride ion with the
formation of trifluoromethyl derivatives is also
possible. At elevated temperatures, the oxirane ring
can undergo thermolysis with the elimination of
difluorocarbene.
With NaF as catalyst, only slow evolution of small
amounts of carbonyl difluoride and sulfuryl difluoride
was observed (run no. 15). Addition of KF led only to
an increase in the intensity of their evolution and to
tarring of the reaction mixture.
AFSO starts to decompose at 60–65°C, which
coincides with the decomposition temperatures of
perfluoroalkyl fluorosulfates [8]. Attempts to perform
an isomerization of AFSO (by analogy with HFPO) at
low temperatures on various catalysts failed.
Presumably, the first step of AFSO decomposition by
the ionic mechanism is formation of a transition
complex by the attack of the fluoride anion at the
As in isomerization of HFPO to perfluoropropionyl
fluoride, we tested as nucleophilic catalysts Lewis
bases such as tertiary amines, alkali metal fluorides as
sources of ionic fluorine, and the complex of hydrogen
fluoride with triethylamine. The experimental data on
the decomposition of AFSO are given in Table 1.
_
0.150
_
0.156
_
0.365
_
0.291
0.247
_
0.083
0.350
0.391
0.218
We failed to prepare MDF following the protocol
from [1], with CsF as catalyst, because of the
_
0.106
_
0.085
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 82 No. 3 2009

DECOMPOSITION OF PENTAFLUOROALLYL FLUOROSULFATE OXIDE
451
O
F−
O
F
S
O
F
O
CF2−CFCF2OS−F
O
CF2
CFCF2O−
CCF2C
CF2−CFCF2O
−2F−
−SO2F2
F−
F
O
F
O
sulfur atom bearing the largest positive charge in the
molecule. Decomposition of the complex with the
elimination of SO2F2 results in redistribution of the
charge density in intermediate potassium 2,3-epoxyper-
fluoropropylate, and the fluoride anion causes isomeriza-
tion of the oxirane with the formation of MDF:
The best results in decomposition of 15 g (0.065 mol)
of AFSO, with an MDF yield of up to 60 mol %, were
obtained under laboratory conditions in a glass
apparatus at the weight ratio acetonitrile (solvent) : KF
(catalyst) : ethylene glycol (process activator) = 12 :
1.5 : 0.07 at the boiling point of the solvent (run no. 8),
Table 1. Yield of MDF in decomposition of 15 g of AFSO under various conditions
MDF yielda
Run
no.
Amount of crude
product in trap, g
Bottom
residue, g
Medium, ml
Catalyst, g
Activator
Т, °C
wt % mol %
1
2
–
KF, 1
АS-14c, 1
KF, 2
Diglyme, 0.15 ml
Diglyme, 2 ml
Dioxane, 1 ml
Tetraglyme, 1 ml
Diglyme, 1 ml
PEG-400, 1 ml
18-Crown-6-6, 0.5 g
Ethylene glycol, 0.07 g
PEG-1500, 1 g
–
64
64
81
81
81
81
81
81
81
81
81
–
0.5
11
–
–
1
15b
14.5b
4
–
12
38
37
39
32
34
42
29
34
36
3
CH3CN, 15
CH3CN, 15
CH3CN, 15
CH3CN, 15
CH3CN, 15
CH3CN, 15
CH3CN, 15
CH3CN, 15
CH3CN, 15
48
42
49
38.5
39
60
28
39
41
4
KF, 2
10
4
5
KF, 2
11
3
6
KF, 1.7
KF, 1.6
KF, 1.5
KF, 2
10.5
10
4.5
5
7
8
12.5
8.5
10
2.5
5.5
5
9
10
11
KF(sd)d, 1.6
KF, 2; Et3N, 0.2 Dioxane, 1 ml
ml
10
5
12
13
Benzene, 15
Toluene, 15
KF, 2
Dioxane, 1 ml
–
80
85
–
–
–
3
15b
12b
N,N-Dimethyl-
aniline, 0.3
1.5
17
14
CH3CN, 7.5;
DMSO, 7.5
KF, 1
Ethylene glycol, 0.07 g
81
2
4
1
12
15
16
17
18
19
20
CH3CN, 15
CH3CN, 10
CH3CN, 15
CH3CN, 15
CH3CN, 30
CH3CN, 30
NaF, 3; KF, 1
KF, 1
Ethylene glycol, 0.07 g
Ethylene glycol, 0.07 g
[Bu4P]Br, 0.15 g
–
81
81
81
81
81
81
–
7
–
–
4
15b
7
5
KF, 0.4
6.5
3.5
2
24
19
35
41
18
7.5
8
8.5
11.5
13b
2.5
CsF, 0.6
KF(sd), 0.05 g Ethylene glycol, 0.07 g
Et3N·3HF, 2 g
–
13.5
63
a According to GLC data.
b Unchanged AFSO.
c AS-14 is an anion-exchange resin.
d KF(sd) denotes KF dried by vacuum spraying.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 82 No. 3 2009

452
LEBEDEV et al.
and also in the presence of the complex Et3N·3HF in
acetonitrile (run no. 20).
(up to 15 mol %), oxalyl difluoride (up to 5 mol %),
and, unexpectedly, HFP whose yield in some
experiments reached 10 mol %. Apparently, specific
catalytic decomposition of AFSO with the formation
of carbene (see below) occurs concurrently with the
catalytic decomposition of AFSO by the ionic
mechanism via nucleophilic attack of fluoride anion
with the formation of MDF:
In the course of the experiment, the AFSO
decomposition products, including MDF and sulfuryl
difluoride, were removed from the reactor and
condensed in a cooled trap. Among the reaction
products we identified by 19F NMR carbonyl difluoride
O
FSOCF2CF−CF2
O
O
O
O
O
F2C=CFCF2OSF
O
O
KF
FSOCF2C
O
+ :CF2
F2C−CFCF2OSF
−COF2
F
O
O
O
O
F2C=CFCF3 + KOSO2F
SO2F2 +
C−C
COF2 + CO
F
F
The HFP formation can be accounted for by
insertion of difluorocarbene with the formation of AFS
and eliination of carbonyl difluoride, followed by
replacement of the fluorosulfate group of AFS by
fluoride anion. This mechanism can be confirmed by
an unusual reaction of highly electrophilic fluorinated
epoxides with trialkyl phosphites, occurring at room
temperature and yielding trialkoxyphosphorylides [9]:
As for the kinetics of by-product formation, with
the progress of AFSO decomposition the content of
HFP and COF2 in the product mixture increases (see
figure), which contradicts the above scheme, because
fluoride ion is present in catalytic amounts.
Apparently, HFP can be formed not only by
substitution of the fluorosulfate group in AFS by
fluoride anion, but also by elimination of SO3. For
example, Hass et al. [13] showed that FSO2CF2COF is
unstable in the presence of CsF, with one of the
decomposition pathways yielding sulfur dioxide and
trifluoroacetyl fluoride. Krespan and England point to
possible elimination of sulfur trioxide and demonstrate
the reversibility of AFS synthesis from HFP and sulfur
trioxide [2].
OR
RO−P +
OR
OR
RO−P=C
OR
F2C
F3C
O
CF3
CF3
C
−COF2
CF3
The capability of AFS for substitution of the
fluorosulfate group by nucleophilic fluoride anion
under the action of alkali metal fluorides was
demonstrated in [10].
It should be noted that only with Et3N·3HF used as
the catalyst the MDF : HFP ratio remained constant in
the course of the reaction. Apparently, with KF as
catalyst, with the progress of the concurrent
substitution of the fluorosulfate group by fluorine, the
catalyst surface becomes covered with potassium
fluorosulfate, which is less soluble in acetonitrile. As
this product is accumulated in the system, the reaction
direction shifts toward carbene decomposition, which
It could be assumed that HFP is formed via
successive addition of carbene :CF2 with intermediate
formation of tetrafluoroethylene; in this case, however,
the product mixture should contain both tetrafluoro-
ethylene and hexafluorocyclopropane [11, 12] whose
signals were absent from the 19F NMR spectra.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 82 No. 3 2009

DECOMPOSITION OF PENTAFLUOROALLYL FLUOROSULFATE OXIDE
453
is apparently responsible for the observed decrease in
the MDF yield and increase in the yield of by-products
of AFSO decomposition, including HFP.
Somewhat larger content of carbonyl fluoride
according to the results of analysis may be due to
decomposition of oxalyl difluoride because of its
instability under the reaction conditions.
It is necessary to give some comments on the role
of specific catalysis of carbene decomposition of the
oxirane ring. This is a low-temperature (70–80°C)
solution process that distinguishes it from the thermal
process (for HFPO, the threshold temperature of
thermal decomposition with the formation of
difluorocarbene is 150°C [14]). Carbenes generated in
solution, and especially in the presence of metals,
appear to be more or less bound in a complex with the
solvent and/or metal, which affects the lifetime,
effective volume, selectivity, and electrophilic
properties of the carbene [15]. The surface of
crystalline fluoride or fluorosulfonate of potassium or
another metal can act as catalyst. For example, the use
of a magnetic stirrer made of a ferromagnetic alloy
without protective glass shell led to a dramatic increase
in the yield of the reaction by-products. Attempts to
implement the process in a stainless steel apparatus led
to a decrease in the MDF yield to 20 mol % because of
an increase in the yield of the low-boiling components.
Apparently, specific catalysis on the metal surface led
to redistribution of chemical mechanisms in favor of
the carbene decomposition.
Composition of gaseous products of AFSO decom-
position, according to GLC data. (c) Relative content of
compound and (τ) time. (1) COF2, (2) SO2F2, (3) HFP,
and (4) MDF.
Pentafluoroallyl fluorosulfate oxide (bp 64°С) was
prepared according to [2, 4] (yield 60%) and was no
less than 98% pure. Acetonitrile was dried by
distillation from phosphorus pentoxide. Benzene,
toluene, and hexane were distilled from sodium.
Dimethyl sulfoxide and triethylamine were dried with
calcium hydride and distilled. Calcined and dried
potassium fluoride was additionally dried in a vacuum
at 300°С.
AFSO decomposition. A 100-ml three-necked flask
equipped with a magnetic stirrer, a thermometer, a
dropping funnel with pressure compensation, and a
reflux condenser connected by a polyethylene tube to a
glass trap with the outlet protected by calcium chloride
tube was charged in succession in a dry nitrogen
stream with 1 g (0.017 mol) of KF, 0.07 g (0.001 mol)
of ethylene glycol, and 15 ml of acetonitrile. The
funnel was charged with 10 ml (15 g, 0.06 mol) of
AFSO. The heating and stirring were switched on, and
the trap was cooled with an isopropanol–liquid
nitrogen mixture to a temperature from –80 to –90°С.
At 75°С, slow dropwise addition of AFSO was started.
The mixture warmed up and started to boil (81°С). The
evolved decomposition products were condensed in the
trap. The gas phase composition in the course of the
process was monitored by TLC by taking 1-ml samples
of the gas phase with a syringe through a rubber tube
connecting the top of the reflux condenser with the
polyethylene tube. AFSO was added over a period of
90–100 min, after which the mixture was heated for
an additional 30 min. The trap contents (12.5 g) were
finally analyzed by GLC by taking liquid samples. A
sample of decomposition products in a methylene
chloride solution was sealed in a glass insert and
The presence of high-boiling oligomers in the
bottom residue (20–30 wt % based on converted
AFSO) suggests the occurrence of both side processes
of AFSO oligomerization and oxidative reaction of
sulfur trioxide with the solvent.
EXPERIMENTAL
AFSO decomposition products were analyzed chromato-
graphically on an LKhM-8MD instrument [model 5,
thermal conductivity detector, programmed heating
from 30 to 200°C at a rate of 6 deg min–1, 3 mm × 3 m
columns, Silokhrom-80 support (fraction 0.25–0.35
mm, packing density 0.30±0.01 g cm–3), stationary
phase PEF (15 wt %), carrier gas helium (40 ml min–1)].
The 19F NMR spectra were taken on an AM-500
Bruker Spectrospin spectrometer at 470.572 MHz
against internal hexafluorobenzene (δ = –162.9 ppm).
Acetone-d6 was used as solvent. The fluorine chemical
shifts were converted to the δ scale relative to СCl3F.
19
analyzed by F NMR. Composition of the condensate
in the trap (mol %, 19F NMR data): SO2F2 52 (bp –52°С),
(COF)2 2 (bp 0°С), COF2 13.5 (bp –84°С), CF3COF
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 82 No. 3 2009

454
LEBEDEV et al.
Table 2. 19F NMR spectra of identified compounds in AFSO decomposition products
δ, ppm
50.45
–79.3
Multiplet
JF*–F*, Hz
1F–2;3F, 8.3
2F–3F, 145
2F–1;4F, 10
Number ofF atoms
Structure
Referencesa
t
1
1
d.t
3F–2F, 145
3F–1;4F, 7.6
4F–5F, 40.6
4F–6F, 20.3
4F–2;3F, 10
–80.7
d.t
1
1
F4
F2
F3
F5
O
[2]
–109.4
d.d.t
1FSO
O
F6
O
5F–4F, 40.7
5F–6F, 16.5
–112.1
d.d
1
–155.4
–69.0
t
6F–4;5F, 17.8
1
3
7F–9F, 20.3
7F–10F, 12.7
7F–8F, 7.6
d.d.d
8F–9F, 53.4
8F–10F, 38.2
8F–7F, 7.6
9F–10F, 117
9F–8F, 53.4
9F–7F, 20.3
10F–9F, 117
10F–8F, 38.1
10F–7F, 12.7
–91.75
–105.8
–192.9
d.d.q
d.d.q
d.d.q
1
1
1
7F3C
10F
F9
F8
[17]
C
C
21.6
–111.5
21.5
t
t
11F–12F, 10.5
12F–11F, 10.2
13F–15F, 8.9
2
2
1
3
2
1
3
2
2
2
1
1
2
C12F2(CO11F)2
С14F3C15F2CO13F
C17F3CO16F
[18]
[19]
[20]
t
–83.6
–123.1
16.7
s
s
q
d
s
16F–17F, 6.5
17F–16F, 6.0
–74.9
–20.9
23.5
CO18F2
19FOC–CO19F
SO220F2
[21]
[22]
[23]
s
33.8
s
50.2
t
21F–23F, 7.6
22F–23F, 2.5
23F–21F, 7.6
23F–22F, 2.5
15.8
t
22FОСС23F2ОSО2F21
–76.4
d.d
a The spectra are in agreement with the published data.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 82 No. 3 2009

DECOMPOSITION OF PENTAFLUOROALLYL FLUOROSULFATE OXIDE
455
0.5 (bp –59°С), CF3CF2COF 1 (bp –23°С), HFP 5,
MDF 22 (bp –9°С), FOCCF2OSO2F 0.5, AFSO 1, and
unidentified impurities 2.5. The MDF yield and spectra
of the identified compounds are given in Tables 1 and
2. The bottoms were also analyzed by GLC. The
bottoms (2.5 g) after filtering off the salts and distilling
off acetonitrile were a dark red mixture of high-boiling
AFSO oligomers.
5. Ovchinnikov, E.V., Struk, V.A., and Gubanov, V.A.,
Tonkie plenki ftorsoderzhashchikh oligomerov: Osnovy
sinteza, svoistva, primenenie (Thin Films of Fluorinated
Oligomers: Fundamentals of the Synthesis, Properties,
Application), Grodno: GGAU, 2007.
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8. Fokin, A.V., Studnev, Yu.N., Kuznetsova, L.D., and
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Krotovich, I.N., Usp. Khim., 1982, vol. 51, no. 8, p. 1258.
(1) Decomposition of pentafluoroallyl fluorosulfate
oxide under the action of nucleophilic catalysts yields
a multicomponent mixture of products, which suggests
the reaction occurrence along several concurrent
pathways.
9. Kadyrov, A.A. and Rokhlin, E.M., Abstracts of Papers,
IV Vsesoyuznaya konferentsiya po khimii ftororgani-
cheskikh soedinenii (IV All-Union Conf. on Chemistry
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10. Banks, R.E., Birchall, J.M., Haszeldine, R.N., and
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11. Barabanov, V.G. and Ozol, S.I., Piroliticheskie sposoby
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Procedures for Preparing Fluorinated Olefins), St.
Petersburg: Teza, 2000.
(2) Difluoromalonyl difluoride is formed in the
maximal yield (up to 60 mol %) in acetonitrile in the
presence of catalytic amounts of KF and ethylene
glycol, or of the complex Et3N·3HF.
(3) A scheme of formation of the identified by-
products of pentafluoroallyl fluorosulfate oxide
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suggested.
12. Mizukado, J., Matsukawa, Y., Quan, H., et al., J. Fluorine
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(4) In the course of decomposition of penta-
fluoroallyl fluorosulfate oxide in the steady-state
supply mode on potassium fluoride, the composition of
the reaction products changes toward an increase in the
yield of carbene decomposition products (hexafluoro-
propene and carbonyl difluoride), owing to specific
catalysis on the surface of the forming potassium
fluorosulfate.
14. Sargeant, P.B., J. Org. Chem., 1970, vol. 35, p. 678.
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16. Moreland, C.G. and Brey, W.S., J. Chem. Phys., 1964,
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17. Jin, A., Mack, H.G., Waterfeld, A., and Oberhammer, H.,
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by the heterogeneous catalytic effect of the metal
surface.
J. Am. Chem. Soc., 1991, vol. 113, p. 7847.
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