Synthesis of perfluorinated carboxylic acid membrane monomers by utilizing liquid-phase direct fluorination

Article abstract of DOI:10.1016/j.jfluchem.2004.12.002

A new synthetic procedure for the preparation of perfluorinated carboxylic acid membrane monomers from non-fluorinated compounds has been developed. A key step in the synthetic route is liquid-phase direct fluorination reaction with elemental fluorine. Direct fluorination of a partially fluorinated diester, which was prepared from a hydrocarbon diol and a perfluorinated acyl fluoride, followed by thermal elimination, gave a perfluorinated diacyl fluoride, which is a precursor of a perfluorinated carboxylic acid membrane monomer.

Full text of DOI:10.1016/j.jfluchem.2004.12.002

Journal of Fluorine Chemistry 126 (2005) 521–527
www.elsevier.com/locate/fluor
Synthesis of perfluorinated carboxylic acid membrane
monomers by utilizing liquid-phase direct fluorination
*
Takashi Okazoe , Kunio Watanabe, Masahiro Itoh,
Daisuke Shirakawa, Kengo Kawahara, Shin Tatematsu
Research Center, Asahi Glass Co. Ltd., 1150 Hazawa-cho, Kanagawa-ku, Yokohama 221-8755, Japan
Received 22 November 2004; accepted 6 December 2004
Available online 15 January 2005
Dedicated to Professor Richard D. Chambers on the occasion of his 70th birthday.
Abstract
A new synthetic procedure for the preparation of perfluorinated carboxylic acid membrane monomers from non-fluorinated compounds
has been developed. A key step in the synthetic route is liquid-phase direct fluorination reaction with elemental fluorine. Direct fluorination of
a partially fluorinated diester, which was prepared from a hydrocarbon diol and a perfluorinated acyl fluoride, followed by thermal
elimination, gave a perfluorinated diacyl fluoride, which is a precursor of a perfluorinated carboxylic acid membrane monomer.
# 2004 Elsevier B.V. All rights reserved.
Keywords: Acyl fluorides; Direct fluorination; Fluorine; Membrane; Synthesis
1. Introduction
the diacyl fluoride 2 is added to hexafluoropropylene oxide
(HFPO) to give diacyl fluoride 3. Pyrolysis followed by
methanolysis affords the Flemion1 comonomer 5. Although
this chemistry is well-established, it is costly, uses hazardous
reagents, such as oleum and has an iodine-containing waste
problem. Moreover, there are restrictions in the monomer
structure because of the poor variety of raw materials
available.
The ion exchange membrane Flemion1, which was
developed by Asahi Glass, is used as a membrane in the
energy-saving and pollution-free chlor-alkali production
process. Nafion1 (DuPont) is also used for the same
purpose. They surpass the conventional mercury cell or
diaphragm processes [1,2]. Recently, a sulfonate–carbox-
ylate laminated polymer membrane has been used to obtain
an higher concentration of caustic soda. A perfluorinated
carboxylic acid membrane is an important component there
[3].
Flemion1 carboxylic acid is a copolymer of tetrafluor-
oethylene (TFE) and perfluorinated vinyl ether, which has a
carboxylic acid group in the side chain. The conventional
manufacturing process of the Flemion1 comonomer is
shown in Scheme 1 [4].
The Exfluor–Lagow elemental fluorine process is
effective under mild conditions [5–7]. Lagow et al. reported
liquid-phase direct fluorination of non-fluorinated com-
pounds with relatively simple structure, such as octyl
octanoate, and the methodology is a powerful tool for the
synthesis of perfluorinated compounds. Our new synthetic
methodology, the PERFECT (PERFluorination of an
Esterified Compound then Thermal elimination) process,
starts from non-fluorinated compounds and utilizes liquid-
phase direct fluorination as a key step (Scheme 2) [8,9].
A small hydrocarbon component with the backbone
structure of the desired compound in the alcohol form 6 is
made by conventional organic synthesis. Then, 6 is coupled
with a perfluorinated moiety, the desired perfluoroacyl
Diiodide 1 obtained from TFE and iodine, is oxidized
with oleum to give diacyl fluoride 2. Cesium alkoxide from
* Corresponding author. Tel.: +81 45 374 7103; fax: +81 45 374 8858.
E-mail address: takashi-okazoe@agc.co.jp (T. Okazoe).
0022-1139/$ – see front matter # 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.jfluchem.2004.12.002

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T. Okazoe et al. / Journal of Fluorine Chemistry 126 (2005) 521–527
Scheme 1.
fluoride 7 in a typical case, to form a larger partially
fluorinated molecule 8. Perfluorination is achieved by direct
fluorination of the partially fluorinated ester compound 8.
Thus, a vapor-phase reaction is avoided since the substrate 8
has low vapor pressure. In addition, the solubility of the
substrate 8 in perfluorinated solvent significantly increases,
and this is an advantage because we can use various
perfluorinated solvents other than CFCs. Finally, thermal
elimination followed by the separation of the mixture of acyl
fluorides gives the desired perfluorinated compound 10 and
recovered 7.
As an example, we have reported the synthesis of
perfluoro(propyl vinyl ether), PPVE [8,9], perfluorinated
butenyl vinyl ether, BVE, which is the monomer of
transparent perfluorinated cyclic polymer, CYTOP1 [10].
We have also reported the synthesis of perfluoroalkane-
sulfonyl fluorides [11], and perfluoroketones [12].
Herein, we present a new synthesis of the perfluorinated
carboxylic acid membrane monomer using the PERFECT
process. It also serves to provide monomer candidates other
than conventional structures.
2. Results and discussion
2.1. Preparation of substrates for the PERFECT process
Flemion1 monomer 5 is made from diacyl fluoride 2
through diacyl fluoride 3. Therefore, it was postulated that
these perfluorinated diacyl fluorides would be synthesized
by the PERFECT methodology. In the PERFECT metho-
dology, the counterpart of a perfluoroacyl fluoride is the
corresponding alcohol. Therefore, diols 11a and 11b are the
candidates to be starting materials for the PERFECT
process (Scheme 3).
One of the starting non-fluorinated diols, 1,4-butanediol
(11a), is commercially available and inexpensive. On
the other hand, diol 11b must be synthesized, because
it is not commercially available. The synthesis is shown
in Scheme 4.
The starting material was 1-benzyloxy-2-propanol (12)
and was treated with tosyl chloride in pyridine to give
tosylate 13 in 86% yield. Then, reaction of tosylate 13 with
1,4-butanediol gave mono-substituted alcohol 14 in 58%
Scheme 2. The ‘‘PERFECT’’ cycle.

T. Okazoe et al. / Journal of Fluorine Chemistry 126 (2005) 521–527
523
Scheme 3. Retrosynthetic analysis.
Scheme 4.
yield. Elimination of the benzyl group from 14 by catalytic
hydrogenation gave the desired diol 11b in 92% yield.
probably due to C–O bond cleavage by HF in the reaction
mixture.
The next liquid-phase direct fluorination of partially
fluorinated esters was carried out basically in a manner
similar to the Exfluor–Lagow method. In order to control the
reaction, heat removal, use of an inert solvent, appropriate
dilution of both fluorine and the substrate, and an excess
amount of fluorine to replace all of the hydrogen atoms in the
substrate at all times were essential as in the case of non-
fluorinated substrates.
2.2. The PERFECT process for the synthesis of diacyl
fluorides 2 and 3
Esterification of 11 was carried out simply by mixing
the non-fluorinated diol and perfluoropropanoyl fluoride
with removal of HF formed during the reaction from
the reaction system by a stream of nitrogen (Table 1). In the
case of the esterification of 11b, the yield was not high,
In our method, however, dangerous vapor-phase reactions
were avoided by employing a higher-molecular weight
partially fluorinated ester as the substrate. Thus, the reaction
was carried out with 1.5–3.0 equivalents of fluorine diluted
to 20–50% in nitrogen to give the desired perfluoroester in
high yield (Table 2).
Table 1
Esterification
To increase conversion, addition of benzene was effec-
tive in generating a higher concentration of fluorine radicals
[13].
RH2
RF1
Substrate
Product
Yield (%)
R113 (1,1,2-trichlorotrifluoroethane) was used as a
typical solvent on the laboratory scale, but other per-
fluorinated compounds, such as perfluorohexane can also be
used. Ideally, this reaction should be carried out in the
11a
11b
–(CH2)2–
CF3CF2–
CF3CF2–
16a
16b
97a
46
a
Crude yield.

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T. Okazoe et al. / Journal of Fluorine Chemistry 126 (2005) 521–527
Table 2
Direct fluorination
RF1
RH2
RF2
Substrate
Solvent
F2/N2 (%)
Yield (%)a
16a
CF3CF2–
–(CH2)2–
–(CF2)2–
R113
20
50
20
20
92
89
78
94
R113
Perfluorohexane
R113
16b
CF3CF2–
aDetermined by 19F NMR.
Table 3
Thermal elimination
RF1
RF2
Substrate
Amount of NaF (eq)
Product
Yield (%)
17a
17b
CF3CF2–
CF3CF2–
–(CF2)2–
1
2
3
52
77
0.22
product itself as the solvent. However, when sufficient
quantity of the product is not readily available, any available
perfluorinated solvents can be employed.
2.3. Total synthesis for the Flemion1 monomer by using
the PERFECT process
The thermal elimination was carried out with sodium
fluoride as a catalyst at 100 8C to give the desired
perfluorinated diacyl fluorides after separation of the starting
perfluoropropanoyl fluoride (Table 3).
The total synthetic processes for the preparation of the
monomer are shown in Schemes 5 and 6.
As for diacyl fluoride 2 production, 1,4-butanediol
(11a) was employed as the starting material (Scheme 5).
Scheme 5.

T. Okazoe et al. / Journal of Fluorine Chemistry 126 (2005) 521–527
525
Scheme 6.
It was esterified with 2 mol of perfluoropropanoyl fluoride
(15) to obtain the partially fluorinated ester 16a. It was
then perfluorinated with elemental fluorine in the liquid-
phase to give perfluorinated ester 17a. Thermal elimination
The PERFECT methodology does not require oleum, and
has no iodine-containing waste problem.
It does not require an additional solvent when the
product itself is used for the solvent in the direct fluorina
tion step, and HF is the only by-product in the PERFECT
cycle.
afforded the desired perfluorodiacyl fluoride
2 and
perfluoropropanoyl fluoride 15 was recovered. This can
be recycled.
By using the PERFECT process, various new perfluoro-
diacyl fluorides, which are transformed into new Flemion1-
type monomer, can be created.
By repeating the cycle, the quantity of perfluorodiacyl
fluoride 2 will increase. Perfluorodiacyl fluoride 2 once
obtained is reacted with HFPO to give perfluoroacyl fluoride
3, and the following reactions give Flemion1 monomer 5 by
a known process [4].
4. Experimental
In the synthesis of perfluorodiacyl fluoride 3 by the
PERFECT process, HFPO is not required (Scheme 6),
because hydrocarbon backbone structure was synthesized
before fluorination. Thus, diol 11b was esterified with 2 mol
of perfluoropropanoyl fluoride (15), perfluorinated with
elemental fluorine, and dissociated to give the desired
perfluorodiacyl fluoride 3. It is converted to Flemion1
monomer 5 in further two steps.
This methodology is applicable to the synthesis of other
diacyl fluorides as well as Flemion1 precursor 5, and it can
be expected to be useful for various perfluorinated diacyl
fluorides.
4.1. General
NMR spectra were obtained on a JEOL EX-400
1
(tetramethylsilane as internal standard for H, and trichlor-
ofluoromethane for 19F). High resolution mass spectra were
obtained on JEOL SX-102A coupled to HP-5890 with a
60 m capillary column J&W DB-1 or DB-1301. Elemental
fluorine was generated by FluorodecTM 30, Fluoro Gas
(UK). Elemental fluorine is highly toxic and corrosive gas,
and may cause explosion when it meets organics in the
vapor-phase. Extreme care must be taken when handling it!
Both the liquid and vapor of hydrogen fluoride (bp 19.5 8C)
evolved during the reaction are also highly corrosive and
cause severe burns when in contact. Care must be taken!
Prior to use, all hydrocarbon greases must be removed and
the apparatus must be gradually passivated with elemental
fluorine. Although the use of 1,1,2-trichlorotrifluoroethane
(R113) is regulated, we give experimental examples with it
for convenience, because it is still much more cheaply
available (Aldrich) than compound 2 or 3 for use as solvent.
3. Conclusions
Diacyl fluorides, which are precursors of Flemion1
carboxylic acid membrane monomer, were synthesized by
the PERFECT process from non-fluorinated diols by
utilizing direct fluorination with elemental fluorine as a
key step.

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T. Okazoe et al. / Journal of Fluorine Chemistry 126 (2005) 521–527
Care must be taken in order not to emit it to the environment
by using, for example, a rotary evaporator with PTFE
diaphragm-type vacuum pump and cooling trap. Once
enough of the compound 2 or 3 is obtained in the cycle, it
should be used instead of R113. Other reagents were
obtained from Kanto Chemicals (Japan) and used without
purification.
vigorously stirring. A gaseous sample (3.46 g) was
recovered. By the NMR spectrum, it was confirmed that
acyl fluoride 15 and diacyl fluoride 2 [4] were the main
components. The yield of 2 was 52%.
4.2.4. Preparation of CF3CF2COO CH2CH(CH3)
O(CH2)4OCOCF2CF3 (16b)
p-Toluenesulfonyl chloride (63.1 g, 0.331 mol) was
added gradually to HOCH(CH3)CH2OCH2Ph (12, 50.0 g,
0.301 mol) in pyridine (150 ml) with stirring at 5 8C over a
period of 1 h. Then the mixturewas added towater (165 ml),
and extracted with dichloromethane (165 ml). The
organic layer was washed with NaHCO3 (165 ml), further
washed three times with water (130 ml), dried over
magnesium sulfate, filtered and then concentrated by an
evaporator. The precipitated white crystals were collected
by filtration and washed with hexane to obtain tosylate
13 (83.2 g, 0.260 mol, 86%); 1H NMR (300.4 MHz,
4.2. Typical procedure
4.2.1. Preparation of CF3CF2COO(CH2)4OCOCF2CF3
(16a)
While bubbling nitrogen gas, 1,4-butanediol (11a, 200 g,
2.22 mol) was stirred, perfluoropropanoyl fluoride 15
(800 g, 4.82 mol) was introduced at 25–30 8C over a
period of 2.5 h. After completion of the addition, stirring
was continued at room temperature for 15 h. The crude
liquid was washed twice with saturated NaHCO3 aqueous
solution (500 ml) at 20 8C. The organic-phase was washed
three times with water (1 L), and dried over magnesium
sulfate. After filtration, the crude liquid (825 g) was
purified by silica gel column chromatography with R225
(mixture of CF3CF2CHCl2 and CClF2CF2CHClF) as an
eluent and following distillation (91–93 8C/1.0–1.3 kPa)
afforded the partially fluorinated ester 16a (255 g,
0.667 mol, 30.0%). The GC purity was 99%; 1H NMR
(300.4 MHz, CDCl3) d: 1.85–1.89 (m, 4H, CH2), 4.41–4.45
(m, 4H, OCH2); 19F NMR (282.65 MHz, CDCl3) d: À83.0
(6F, CF3), À121.4 (4F, CF2). High resolution mass spectrum
(CI+) 383.0367 ([M + H]+, calculated for C10H9F10O4:
383.0341).
3
CDCl3) d: 1.31 (d, J = 6.3 Hz, 3H, CH3), 2.40 (s, 3H,
CH3C6H4), 3.46 (m, 2H, OCH2CH), 4.41 (m, 2H, OCH2Ph),
4.73 (m, 1H, CH), 7.19–7.34 (m, 7H, C6H5 and 2H of
C6H4), 7.75–7.89 (m, 2H of C6H4). Diol 11a (37 g,
0.41 mol), potassium hydroxide (23 g, 0.41 mol) and
dioxane (200 ml) were heated to an internal temperature
of 102 8C to dissolve potassium hydroxide. A solution
of tosylate 13 (63.7 g, 0.199 mol) obtained above in
dioxane (65 ml) was added dropwise over a period of 1 h
and stirred for 4 h. The reaction mixture was added to water
(350 ml) and extracted three times with dichloromethane
(100 ml). The organic layer was washed with water (20 ml),
dried over magnesium sulfate, filtered, concentrated and
purified by silica gel column chromatography to obtain
compound 14 (27.6 g, 0.116 mol, 58%); 1H NMR
4.2.2. Synthesis of CF3CF2COO(CF2)4OCOCF2CF3
(17a)
3
(300.4 MHz, CDCl3) d: 1.15 (d, J = 6. 2 Hz, 3H, CH3),
Into a 3000 ml autoclave made of nickel, R113 (3232 g)
was charged, stirred and maintained at 25 8C. At the gas
outlet of the autoclave, a cooler maintained at À10 8C was
installed. After supplying nitrogen gas for 1 h, 20% F2/N2
was supplied for 1 h at a flow rate of 8.49 L/h for 2.3 h. Then,
while supplying 20% fluorine gas at the same flow rate, a
solution of compound 16a (80 g, 0.209 mol) in R113 (800 g),
was injected over a period of 45.7 h. Further, 20% fluorine
gas was supplied at the same flow rate for 0.5 h, and then
nitrogen gas was supplied for 3.0 h to remove volatile
materials.
1.64 (m, 4H, CH2), 2.98 (bs, 1H, OH), 3.62–3.68 (m, 7H,
OCH2 and CH), 4.53 (m, 2H, OCH2Ph), 7.23–7.29 (m, 5H,
C6H5).
Under an argon atmosphere, 5% palladium–carbon
powder (1.5 g) was charged. Compound 14 (15.2 g,
63.8 mmol) in ethanol (100 ml) was added. The mixture
was stirred at room temperature for 17 h and then filtered
through celite. The filtrate was concentrated to obtain
compound 11b (8.65 g, 58.4 mmol, 92%); 1H NMR
(300.4 MHz, CDCl3) d: 1.11 (q, 3J = 6.2 Hz, 3H, CH3),
1.68 (m, 4H, CH2), 2.48 (bs, 2H, OH), 3.41–3.68 (m, 7H,
OCH2 and CH). Diol 11b (18.8 g, 0.127 mol) was stirred
at 30 8C, then perfluoropropanoyl fluoride (15, 276 g,
1.66 mol) was supplied together with nitrogen over 6 h
while maintaining the internal temperature at 30 8C.
After completion of the addition, stirring was continued
for 2 h at 30 8C while supplying nitrogen gas. A 5%
NaHCO3 aqueous solution (300 ml) was added at 15 8C.
The organic layer was separated, washed twice with water
(100 ml), dried over anhydrous magnesium sulfate and
then filtered to obtain a crude liquid. The crude liquid was
purified by silica gel column chromatography (eluent: R225)
The yield of the perfluorinated ester 17a determined by
19F NMR spectroscopy was 92%; 19F NMR (376.0 MHz,
CDCl3) d: À83.8 (6F, CF3), À87.3 (4F, OCF2), À122.6
(4F, CF3CF2), À126.6 (4F, OCF2CF2). High resolution
mass spectrum (EI+) 506.9536 ([M À F]+, calculated for
C10F17O4: 506.9525).
4.2.3. Synthesis of FCO(CF2)2COF (2)
Perfluorinated diester 17a (5.00 g, 9.51 mmol) was
charged together with 0.4 g of NaF powder into a flask
and heated at 100 8C for 0.25 h in an oil bath while

T. Okazoe et al. / Journal of Fluorine Chemistry 126 (2005) 521–527
527
to obtain 16b (25.9 g, 58.8 mmol, 46%); 1H NMR
Acknowledgement
(300.4 MHz, CDCl3) d: 1.20 (d, 3J = 6.3 Hz, 3H, CH3),
1.56–1.68 (m, 2H, CH2), 1.78–1.87 (m, 2H, CH2CH2OCO),
3.42–3.60 (m, 2H, OCH2), 3.66–3.76 (m, 1H, OCH), 4.26–
4.42 (m, 4H, COOCH2); 19F NMR (282.7 MHz, CDCl3) d:
À83.0 (6F, CF3), À121.4 (2F, CF2), À121.5 (2F, CF2).
High resolution mass spectrum (CI+) 441.0768 ([M + H]+,
calculated for C13H15F10O5: 441.0760).
We would like to thank Professor Richard D. Chambers
for helpful discussions.
References
[1] M. Yamabe, H. Miyake, Fluorinated membranes, in: R.E. Banks, B.E.
Smart, J.C. Tatlow (Eds.), Organofluorine Chemistry: Principles and
Commercial Applications, Plenum Press, New York, 1994, pp. 403–
411.
4.2.5. Synthesis of CF3CF2COO CF2CF(CF3)O(CF2)4
OCOCF2CF3 (17b)
[2] T. Hiyama, Organofluorine Compounds, Springer, Berlin, 2000, pp.
228–230.
The direct fluorination of 16b was carried out in a
manner similar to the procedure for the direct fluorination
of 16a, where the flow rate of 20% F2/N2 was 10.1 L/h,
and a solution of 16b (4.95 g, 11.2 mmol) in R113 (100 g)
was supplied over a period of 5.5 h. Then, a solution of
benzene in R113 (0.01 g/mL, 9 mL) was supplied inter-
mittently at 0.20 MPa, and this operation was repeated
four times. Nitrogen gas was supplied to remove solvent
and volatile materials to give the crude perfluorinated
product. The structure of the desired product 17b was
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229–270.
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confirmed by 19F NMR and the yield determined by the 19
F
[7] T.R. Bierschenk, T. Juhlke, H. Kawa, R.J. Lagow, US Patent 5093432
(1992).
NMR was 94%; 19F NMR (376.0 MHz, CDCl3) d: À80.4
(3F, CF(CF3)), À81.0 (2F, CF(CF3)OCF2), À83.3 (3F,
CF2CF3), À83.4 (3F, CF2CF3), À86.8 (2F, COOCF2),
À86.9 (2F, COOCF2), À122.1 (4F, CF2CF3), À125.9 (2F,
OCF2CF2), À126.2 (2F, OCF2CF2), À145.6 (1F, CF). High
resolution mass spectrum (EI+) 672.9378 ([M À F]+,
calculated for C13F23O5: 672.9378).
[8] T. Okazoe, K. Watanabe, M. Itoh, D. Shirakawa, H. Murofushi, H.
Okamoto, S. Tatematsu, Adv. Synth. Catal. 343 (2001) 215–219.
[9] T. Okazoe, K. Watanabe, M. Itoh, D. Shirakawa, H. Murofushi, H.
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Okamoto, M. Itoh, S. Tatematsu, Abstract of the 25th Fluorine
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Kawahara, I. Kaneko, S. Tatematsu, J. Fluorine Chem. 125 (2004)
1695–1701.
4.2.6. Synthesis of FCOCF(CF3)O(CF2)3COF (3)
The thermal elimination of 17b was carried out in a
manner similar to the procedure for the thermal elimination
of 17a. The yield of the desired product 3 [4] determined by
the 19F NMR was 77%.
[12] T. Okazoe, K. Watanabe, S. Tatematsu, M. Itoh, D. Shirakawa, M.
Iwaya, H. Okamoto, Abstract of the 16th Winter Fluorine Conference,
Paper 96, 2003.
[13] T. Ono, Chimica Oggi 39 (2003).