Synthesis and some chemical properties of 1-aryloxy-2-chloro-1,2- difluoroethenes

Article abstract of DOI:10.1016/j.jfluchem.2005.06.012

A convenient method of synthesis of 1-aryloxy-2-chloro-1,2-difluoroethenes 1a-h and 1,2-di(aryloxy)-1,2-difluoroethenes 2a-d by the reaction of 1,2-dichloro-1,2-difluoroethene with substituted phenols was developed. Compounds 1a-c treated with n-C₄

Full text of DOI:10.1016/j.jfluchem.2005.06.012

Journal of Fluorine Chemistry 126 (2005) 1307–1311
www.elsevier.com/locate/fluor
Synthesis and some chemical properties of
1-aryloxy-2-chloro-1,2-difluoroethenes
*
Alexei I. Mushta, Mikhail M. Kremlev
Department of Fluorine Chemistry, Institute of Organic Chemistry, National Academy of Sciences of Ukraine,
Murmanskaya st. 5, UA-02094 Kiev, Ukraine
Received 10 January 2005; received in revised form 29 June 2005; accepted 30 June 2005
Available online 25 July 2005
Abstract
A convenient method of synthesis of 1-aryloxy-2-chloro-1,2-difluoroethenes 1a–h and 1,2-di(aryloxy)-1,2-difluoroethenes 2a–d by the
reaction of 1,2-dichloro-1,2-difluoroethene with substituted phenols was developed. Compounds 1a–c treated with n-C4H9Li and then with
CO2 and I2 formed 3-aryloxy-2,3-difluoroacrylic acids 3a–e or 1-aryloxy-2-iodo-1,2-difluoroethenes 4a,c, respectively. Reaction of lithium
derivative of 1-(4-methylphenoxy)-2-chloro-1,2-difluroethene 1c with DMF or N-formylpiperidine gave 3-(4-methylphenoxy)-3-(dimethy-
lamino or piperidin-1-yl)-2-fluoropropenal 5c, 6c.
# 2005 Elsevier B.V. All rights reserved.
Keywords: Phenols; 1,2-Dichloro-1,2-difluoroethene; 1-(Aryloxy)-2-chloro-1,2-difluoroethenes; 1,2-Di(aryloxy)-1,2-difluoroethenes
1. Introduction
oethene in acetone in the presence of potassium hydroxide
with the formation of 4-methoxycarbonylaminophenyl(1,2-
difluoro-2-chloroethenyl)sulfide. The reaction apparently
occurred in two stages: the addition of substituted
thiophenol to 1,2-dichloro-1,2-fluoroethene, followed by
the dehydrochlorination process [5].
The synthetic methods for the addition of substituted
phenols to chlorotrifluoroethene are well established [1,2],
and these compounds are used for the synthesis of herbicides
and pesticides [3]. However, the general procedures for the
substitution of fluorine atom in chlorotrifluoroethene by an
aryloxy fragment with the formation of the corresponding
olefins of general formula ArOCF = CFCl are limited so far
to very few examples. The only synthetic procedure
described in literature was the preparation of 1-(pheny-
loxy)-2-chloro-1,2-difluoroethene by the reaction of sodium
phenolate with chlorotrifluoroethene in anhydrous diethyl
ether [4].
2. Results and discussion
It was found that substituted phenols containing electron
donating or electron withdrawing groups in para-position of
benzene ring did not react with 1,2-dichloro-1,2-difluor-
oethene in the presence of potassium hydroxide in acetone as
a solvent even under reflux. In spite of its low boiling point
1,2-dichloro-1,2-difluoroethene has good solubility in
acetone and is present in a boiling mixture.
We decided to develop a simpler method for the synthesis
of such types of compounds by the reactions of substituted
phenols with a industrial example of 1,2-dichloro-1,2-
difluoroethene.
However, the reaction of substituted phenols with 1,2-
dichloro-1,2-difluoroethene in N,N-dimethylformamide
(DMF) or N,N-dimethylacetamide (DMA) in the presence
of potassium hydroxide in a 1.25:1 molar ratio to phenol at
75–80 8C allows the preparation of compounds 1a–h in good
yields (Scheme 1).
Previously, we showed that 4-methoxycarbonylami-
nothiophenol easily reacted with 1,2-dichloro-1,2-difluor-
* Corresponding author. Tel.: +38 44 5510652; fax: +38 44 5732643.
E-mail address: kremlyov1@yandex.ru (M.M. Kremlev).
0022-1139/$ – see front matter # 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.jfluchem.2005.06.012

1308
A.I. Mushta, M.M. Kremlev / Journal of Fluorine Chemistry 126 (2005) 1307–1311
Scheme 1.
The use of excess of KOH is necessary because it takes
group. s-Constants were determined by 19F NMR
spectroscopy and calculated by equations described in
[7]. It appears, that s-constants of E- and Z- –OCF = CFCl
groups are equivalent for the both fragments: sI 0.52,
sR À0.28, sP 0.24. It is seen from these data that E- and
Z-isomers of ClCF = CFO-group possess acceptor proper-
ties, compared with E- (sI 0.1, sR 0.1,sP 0.20) and Z-1,
2-difluoro-2-chlorovinyl (sI 0.2, sR 0.06, sP 0.26) groups
[8].
part in the addition of 1,2-dichloro-1,2-difluoroethene to
phenol as a catalyst and in the elimination of HCl from the
intermediate product. Decrease in the amount of KOH does
not raise the yields of the desired compounds; this was
shown by a special experiment.
Similarly to the reactivity of 4-methoxycarbonylami-
nothiophenols [5], this reaction apparently occurs in two
stages: first by the addition of substituted phenol to 1,2-
dichloro-1,2-difluoroethene, followed by the elimination of
hydrogen chloride.
The chlorine atom in the ClCF = CFO-series of
compounds 1a,c,d can be substituted with lithium using
n-butyllithium. Treatment of lithium derivatives with carbon
dioxide or iodine leads to the formation of 3-aryloxy-2,3-
difluoroacrylic acids 3a,c,d or 1-(aryloxy)-2-iodo-1,2-
difluoroethenes 4a,c (Scheme 2).
Compounds 3a,c,d and 4a,c are a 1:1 mixture of E- and Z-
isomers according to 19F NMR spectroscopy. In contrast to
the compounds 1a,c,d para-substituted derivatives of a,b-
difluoro-b-chlorostyrene which are a 1:3 mixture of E- and
Z-isomers form only stable E-difluorostyryllithium deriva-
tives on the interaction of n-butyllithium, and their products
of reaction with various substrates contain only E-
difluorovinylene links [9].
Treatment of the compounds 1a–d with the substituted
phenols in DMA in the presence of potassium hydroxide
leads to the formation of 1,2-di(aryloxy)-1,2-difluoroethene
2a–d in 50–60% yield (Scheme 1). 1,2-Di(aryloxy)-1,2-
difluoroethenes 2a–d could be obtained by the reaction of
two moles of the corresponding phenol with one mole of 1,2-
dichloro-1,2-difluoroethene (Scheme 1).
Technical 1,2-dichloro-1,2-difluoroethene exists as a 1:1
mixture of E- and Z-isomers [6]. The same E- and Z-isomer
ratio was determined for the compounds 1a–h. In contrast to
the compounds 1a–h, compounds 2a–d are single isomers as
determined by 19F NMR spectroscopy. Due to the symmetry
of compounds 2a–d, we may assume that they are E-isomers
according to the chemical shifts of signals in 19F NMR
spectra, compared with the chemical shifts in the 19F NMR
spectra of Z-isomers 1a–h.
The reactions of lithium derivative of compound 1c with
DMF or N-formylpiperidine lead to the formation of
products 5c, 6c with the aldehyde function and dimethy-
lamino- 5c or piperidine fragment 6c bonded to the b-carbon
atom of the vinylene link (Scheme 2).
We prepared meta- and para-fluorosubstituted 1-
(fluorophenoxy)-2-chloro-1,2-difluoroethenes 1g,h for
the determination of s-constants of the ClCF = CFO-
These reactions showed the difference of lithium
derivative of compound 1c from difluorostyryllithium
Scheme 2.

A.I. Mushta, M.M. Kremlev / Journal of Fluorine Chemistry 126 (2005) 1307–1311
1309
derivatives, which have formed substituted E-a,b-difluor-
3.2. Preparative procedures
ocinnamaldehydes under similar reaction conditions. The
products of substitution of b-fluorine atom by piperidine
fragment were obtained only by the reaction of E-a,b-
difluorocinnamaldehyde derivatives with excess of piper-
idine. The aldehyde group in the last case shows no
reactivity [10].
3.2.1. 1-(aryloxy)-2-chloro-1,2-difluoroethenes (1a–h)
A mixture of 40 mmol of the corresponding substituted
phenol, 50 mmol of potassium hydroxide, 50 mmol of 1,2-
dichloro-1,2-difluoroethene and 30 ml of DMF or DMAwas
stirred for 10 h at 75–80 8C. Reaction mixture was cooled to
room temperature and poured into water. Organic layer was
extracted with diethyl ether, the extract was washed with 4%
aqueous potassium hydroxide, water, dried over magnesium
sulfate and distilled (see Tables 1 and 2).
Coupling constants of aldehyde group hydrogen atom
and fluorine in the compounds 5c and 6c (JFH = 19.5 Hz) are
similar to the JFH in derivatives of E-a,b-difluorocinna-
maldehydes [10].
3. Experimental
3.2.2. 1.2-Di(aryloxy)-1,2-difluoroethenes (2a–d)
A. A mixture of 10 mmol of corresponding compounds
(1a–d), 25 mmol of potassium hydroxide, 10 mmol of
substituted phenol and 30 ml of fresh distilled DMAwas
stirred for 10 h at 75–80 8C. Reaction mixture was
cooled to room temperature and poured into water.
Organic layer was extracted with diethyl ether, extract
was washed with 4% aqueous potassium hydroxide,
water, dried over magnesium sulfate and distilled or
crystallised for 2d (see Tables 1 and 2).
3.1. General
All chemicals were of reagent grade or were purified by
1
standard methods before use. H, 19F NMR spectra were
recorded at 299.95 and 282.2 MHz respectively with a
Varian VXR-300 spectrometer. Chemical shifts are given in
ppm relative to Me4Si and CFCl3, respectively as internal
standard. Coupling constants are given in Hz. Melting point
were determined in open capillaries and are uncorrected.
Reactions of lithium derivatives were carried out in
anhydrous solvents and under inert (Ar) atmosphere.
B. A mixture of 20 mmol of the corresponding substituted
phenol, 25 mmol of potassium hydroxide, 10 mmol of
1,2-dichloro-1,2-difluoroethene and 30 ml of fresh
Table 1
Yields, physicals constants and analysis of compounds 1–6
t
Sample number Yield B.p. (8C)
M.p.
nD
Analysis
Found
(%)
(mm Hg)
(8C)
Formula
Calcd.
1a
47
21–23 (0.4)
1.480018 C 50.50; H 2.60; Cl 18.60; C8H5ClF2O
F 19.85
C 50.40; H 2.60; Cl 18.60; F 19.90.
1b
1c
1d
1e
1f
54
49
56
99
19
19
27–29 (0.07)
27–29 (0.07)
40–41 (0.4)
1.484012 C 53.10; H 3.70; Cl 17.40
1.481318 C 52.60; H 3.50; Cl 17.20
1.495015 C 48.80; H 3.20; Cl 16.40
C 48.70; H 3.50 Cl 14.20
C9H7ClF2O
C9H7ClF2O
C9H7ClF2O2
C 52.80; H 3.40; Cl 17.40.
C 52.80; H 3.40; Cl 17.40.
C 49.00; H 3.20; Cl 16.10.
49–50
C10H8ClF2NO2 C 48.50; H 3.20; Cl 14.30.
44–46 (0.4)
48–50 (20)
1.520019 C 35.35; H 1.30; F 14.00
C8H4BrClF2O
C 35.60; H 1.50; F 14.10
C 46.00; H 1.90; Cl 17.00;
F 27.00
1g
C 45.75; H 2.00; Cl 17.00; C8H4ClF3O
F 26.80
1h
2a
19
28–30 (0.7)
C 45.70; H 1.80; Cl 16.70; C8H4ClF3O
F 26.90
C 46.00; H 1.90; Cl 17.00;
F 27.00
A. 45 94–95 (0.4)
B. 30
C 67.80; H 4.00
C 69.40; H 5.10
C 69.50; H 5.10
C 62.30; H 4.40
C
14H10F2O2
C 67.70; H 4.00.
2b
2c
2d
A. 40 112–114 (0.4)
B. 19
C16H14F2O2
C16H14F2O2
C 69.60; H 5.10
C 69.60; H 5.10
C 62.30; H 4.55
A. 45 116–118 (0.4)
B. 18
A. 35
B. 14
50
29–30
C16H14F2O4
C9H6F2O3
3a
3c
3d
4a
62–63
C 53.90; H 2.95; F 19.00
C 55.85; H 3.70; F 17.55
C 52.10; H 3.70; F 16.35
C 33.75; H 1.50; I 44.70;
F 13.40
C 54.00; H 3.00; F 19.00
C 56.10; H 3.70; F 17.75
C 52.20; H 3.50; F 16.50
C 34.00; H 1.80; I 45.00;
F 13.50
31
72–73
C
10H8F2O3
10H8F2O4
40
110–111
C
75
50
43–45 (0.4)
C8H5IF2O
C9H7IF2O
C12H14FNO2
4c
53–55 (0.35)
C 36.20; H 2.20; I 42.80;
F 12.50
C 36.50; H 2.40; I 42.90;
F 12.80
5c
6c
41
32
98–100
90–92
C 64.30; H 6.30; N 6.50
C 68.40; H 6.60; N 5.40
C 64.60; H 6.30; N 6.30
C 68.40; H 6.80; N 5.30
C15H18FNO2

1310
A.I. Mushta, M.M. Kremlev / Journal of Fluorine Chemistry 126 (2005) 1307–1311
Table 2 (Continued)
Table 2
1H and 19F NMR data of compounds 1–6
Number Nucleus
d
Splitting J (Hz)
Number Nucleus
d
Splitting J (Hz)
7.10
7.30
À120.5
t
d
s
JHH = 7.4 Hz, 1H, arom., para-H
JHH = 7.4 Hz,2H, arom., meta-H
1a
1H
7.1
d
t
JHH = 8.4 Hz, 2H, arom., ortho-H
JHH = 7.84 Hz,1H, arom., para-H
19F
2F
7.2
7.4
d
d
d
d
d
JHH = 7.8, 2H, arom., meta-H
E-isomer: JFF = 41 Hz F2
JFF = 41 Hz F1
Z-isomer: JFF = 120 Hz, F2
JFF = 120 Hz, F1
2b
1H
2.30
6.80
6.90
7.19
s
m
d
t
3H (CH3)
19F
À102.2
À127.9
À117.8
À134.2
2H, H arom.
1H, H arom.
JHH = 7.51 Hz, 1H, arom., H5)
19F
1H
À120.7
s
2F
1b
1H
2.4
s
d
d
t
3H (CH3)
2c
2d
3a
2.30
7.00
7.10
s
d
d
s
3H(CH3)
HH = 8.2 Hz, 2H, arom., H2,6
6.9
JHH = 6.3 Hz, 2H, arom., H2,6
JHH = 7.5 Hz, 1H, arom., H4
JHH = 6.3 Hz, 1H, arom., H5
E-isomer: JFF = 41 Hz, F2
JFF = 41 Hz, F1
J
JHH = 8.2 Hz, 2H, arom., H3,5
7.02
7.29
19F
1H
À121.0
2F
19F
À102.0
d
d
d
d
3.70
6.80
6.90
s
d
d
s
3H(OCH3)
À128.0
À117.5
À134.4
JHH = 8.0 Hz, 2H, arom., H2,6
JHH = 8.0 Hz, 2H, arom., H3,5
2F
Z-isomer: JFF = 120 Hz, F2
JFF = 120 Hz, F1
19F
1H
À122.5
1c
1d
1e
1H
2.34
s
3H (CH3)
7.40
7.50
7.70
m
m
m
2H, H arom.
1H, H arom.
2H, H arom.
7.00
7.16
d
d
d
d
d
d
JHH = 8.0 Hz, 2H, arom., H2,6
JHH = 8.0 Hz, 2H, arom., H3,5
E-isomer: JFF = 41 Hz, F2
JFF = 41 Hz, F1
19F
À102.0
11.7 broad-s 1H, COOH
À128.4
À117.6
À134.8
19F
À77.0
d
d
d
d
E-isomer: JFF = 19.8 Hz, F1
Z-isomer: JFF = 120 Hz, F2
JFF = 120 Hz, F1
À173.5
À92.0
JFF = 19.8 Hz, F2
Z-isomer: JFF = 120 Hz, F1
JFF = 120 Hz, F2
1H
3.79
s
3H (OCH3)
À180.8
6.90
7.16
d
d
d
d
d
d
J
HH = 9.0 Hz, 2H, arom., H2,6
3c
1H
2.30
s
d
d
3H (CH3)
JHH = 9.0 Hz, 2H, arom., H3,5
E-isomer: JFF = 38 Hz, F2
JFF = 38 Hz, F1
Z-isomer: JFF = 120 Hz, F2
JFF = 120 Hz, F1
7.50
7.70
J
HH = 8.0 Hz, 2H, arom., H2,6
19F
À102.0
JHH = 8.0 Hz, 2H, arom., H3,5
À128.7
À117.5
À135.1
8.10 broad-s 1H, COOH
19F
À84.0
d
d
d
d
E-isomer: JFF = 19.8 Hz, F1
À169.0
À97.2
JFF = 19.8 Hz, F2
1H
2.10
s
t
3H (CH3)
1H, arom., H5
Z-isomer: JFF = 120 Hz, F1
JFF = 120 Hz, F2
6.90
7.40
7.60
À176.5
d
s
JHH = 5.4 Hz, 2H, arom., H2,6
3d
1H
3.80
s
d
d
3H (OCH3)
JHH = 8.0 Hz, 2H, arom., H2,6
JHH = 8.0 Hz, 2H, arom., H3,5
1H, H arom.
6.90
7.80
10.2
s
1H, NH
E-isomer: JFF = 41 Hz, F2
JFF = 41 Hz, F1
Z-isomer: JFF = 120 Hz, F2
JFF = 120 Hz, F1
19F
À102.0
À128.4
À117.4
À134.5
d
d
d
d
10.5 broad s 1H, COOH
19F
À77.5
d
d
d
d
E-isomer: JFF = 19.8 Hz, F1
JFF = 19.8 Hz, F2
Z-isomer: JFF = 120 Hz, F1
JFF = 120 Hz, F2
À175.0
À92.3
1f
1H
7.20
d
d
d
d
d
d
JHH = 8.7 Hz, 2H, arom., H2,6
JHH = 8.7 Hz, 2H, arom., H3,5
E-isomer: JFF = 41 Hz, F2
JFF = 41 Hz, F1
Z-isomer: JFF = 120 Hz, F2
JFF = 120 Hz, F1
À182.6
7.1
7.60
4a
4c
5c
1H
d
t
JHH = 7.5 Hz, 2H, arom., ortho-H
JHH = 7.5 Hz, 1H, arom., para-H
19F
À102.8
7.2
À127.5
À118.3
À133.6
7.3
d
d
d
d
d
JHH = 7.8 Hz, 2H, 2arom., meta-H
E-isomer: JFF = 33 Hz F2
JFF = 33 Hz F1
Z-isomer: JFF = 130 Hz, F2
JFF = 130 Hz, F1
19F
À90.2
À132.3
À111.5
À138.4
1g
1H
7.10
m
m
d
2H, H arom.
7.28
2H, H arom.
E-isomer: JFF = 41 Hz, F2.
J
FF = 41 Hz, F1
19F
À102.8
1H
2.30
s
3H (CH3)
J
HH = 8.7 Hz, 2H, arom., H2,6
JHH = 8.7 Hz, 2H, arom., H3,5
E-isomer: JFF = 36 Hz, F2
JFF = 36 Hz, F1
Z-isomer: JFF = 130 Hz, F2
JFF = 130 Hz, F1
À127.3
À110.4
À118.5
À133.6
À110.4
d
7.00
7.20
d
d
d
d
d
d
m
d
1F, F arom.
Z-isomer: JFF = 119 Hz, F2
JFF = 119 Hz, F
1F, F arom.
19F
À90.3
d
À132.2
À111.7
À138.5
m
1h
2a
19F
À102.5
À127.7
À118.4
À118.1
À133.6
À118.1
d
d
E-isomer: JFF = 41 Hz, F2
JFF = 41 Hz, F1
1H
2.30
s
m
d
3H (CH3)
m
d
1F, F arom.
3.00
7.00
7.50
9.20
6H (2-CH3)
HH = 8.9 Hz, 2H, arom., H2,6
Z-isomer: JFF = 120 Hz, F2
JFF = 120 Hz, F1
1F, F arom.
J
d
d
JHH = 8.9 Hz, 2H, arom., H3,5
m
d
JHF = 19.5 Hz, COH
1H
7.00
d
JHH = 8.3 Hz, 2H, arom., ortho-H
19F
À179.7
d
JFH = 19.5 Hz, 1F

A.I. Mushta, M.M. Kremlev / Journal of Fluorine Chemistry 126 (2005) 1307–1311
1311
Table 2 (Continued )
mixture of 10 ml diethyl ether and 10 ml THF at À85 8C.
The reaction mixture was stirred at À75 8C 1.5 h warmed to
ambient temperature and poured into aqueous hydrogen
chloride with ice. Organic layer was extracted with diethyl
ether, washed with water, dried over magnesium sulfate and
distilled (see Tables 1 and 2).
Number Nucleus
d
Splitting J (Hz)
6c
1H
0.60
m
m
m
s
4H
0.70
1.70
1.50
6.20
6.40
8.20
4H
2H
3H (CH3)
d
J
HH = 8.4 Hz, 2H, arom., H2,6
d
JHH = 8.4 Hz, 2H, arom., H3,5
d
JHF = 19.6 Hz, COH
19F
À111.7
d
JFH = 19.6 Hz, 1F
3.2.5. Reactions of compound 1c with DMF or
N-formylpiperidine
ArOCF1 = CF2Cl (1); ArOCF = CFOAr (2); ArOCF2 = CF1COOH
(3); (4); ArOC(N(CH3)2) = CFCOH (5);
ArOCF1 = CF2I
(6).
To the mixture of 21 mmol of a substituted arene 1c,
10 ml diethyl ether, 20 ml THF under stirring at À85 8C was
added dropwise 14 ml 1.4 N n-butyl lithium in hexane for
30 min. After stirring at À85 8C for 1 h was added dropwise
21 mmol of DMF or N-formylpiperidine in a mixture of 5 ml
diethyl ether and 5 ml THF at À85 8C. The reaction mixture
was stirred at À75 8C 2.5 h warmed to ambient temperature
and poured into 5% aqueous ammonium chloride with ice.
Organic layer was extracted with diethyl ether, washed with
water, dried over magnesium sulfate. Solvent was removed
in vacuum and residue crystallised from diethyl ether:
hexane in a ratio 1:1 (see Tables 1 and 2).
distilled DMAwas stirred for 30 h at 75–80 8C. Reaction
mixture was cooled to room temperature and poured into
water. Organic layer was extracted with diethyl ether,
extract was washed with 4% aqueous potassium
hydroxide, water, dried over magnesium sulfate and
distilled or crystallised for 2d (see Tables 1 and 2).
3.2.3. 3-Aryloxy-2,3-difluoroacrylic acids (3a,c,d)
To the mixture of 21 mmol of corresponding substituted
arene (1a,c,d), 10 ml diethyl ether, 20 ml THF under stirring
at À85 8C was added dropwise 14 ml 1.4 N n-butyllithium
in hexane for 30 min. The reaction mixture was stirred at
À85 8C for 1 h and poured into dry ice. A mixture was
warmed to ambient temperature and extracted with 5%
aqueous sodium carbonate. Aqueous solution was acidified
with aqueous hydrogen chloride, extracted with diethyl ether
dried over magnesium sulfate. Solvent was removed in
vacuum, residue crystallised from diethyl ether: hexane in
ratio 1:1 (see Tables 1 and 2).
References
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[3] German patent no. 3213152 (1983) C.A. 100 (1984), 68527r.
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E.S. Ryabtseva, Dyes Pigments 27 (1995) 183–190.
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3.2.4. 1-(aryloxy)-2-iodo-1,2-difluoroethenes (4a,c)
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(1991) 559–560 (Russ) C.A., 115 (1991) 49267z.
To the mixture of 21 mmol of a corresponding substituted
arene 1a,c, 10 ml diethyl ether, 20 ml THF under stirring at
À85 8C was added dropwise 14 ml 1.4 N n-butyllithium in
hexane for 30 min. After stirring at À85 8C for 1 h was
added dropwise the solution of 21 mmol of iodine in a
[9] M.M. Kremlev, L.M. Yagupolskii, J. Fluor. Chem. 91 (1998) 109–123.
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