Preparative-scale one-pot syntheses of hexafluoro-1,3-butadiene

Article abstract of DOI:10.1016/j.jfluchem.2008.01.015

Hexafluoro-1,3-butadiene, with its negligible global warming potential, is required in quantities for application in plasma dielectric etching in semiconductor industry and as gaseous microbubble suspension contrast agents in diagnostic ultrasound imaging. Three efficient protocols for the preparation of perfluoro-1,3-butadiene in 62-70% overall yields have been described. They involve the coupling of (1) iodotrifluoroethylene (ITFE) with activated copper, (2) trifluorovinylzinc bromide in the presence of copper (II) or iron (III) salts and (3) trifluorovinylzinc chloride, prepared from 1,1,1,2-tetrafluorethane (HFC 134a) in the presence of copper (II) or iron (III) salts.

Full text of DOI:10.1016/j.jfluchem.2008.01.015

Available online at www.sciencedirect.com
Journal of Fluorine Chemistry 129 (2008) 443–446
www.elsevier.com/locate/fluor
Preparative-scale one-pot syntheses of hexafluoro-1,3-butadiene
*
P. Veeraraghavan Ramachandran , G. Venkat Reddy
Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, IN 47907-2084, United States
Received 22 January 2008; accepted 24 January 2008
Available online 3 February 2008
Abstract
Hexafluoro-1,3-butadiene, with its negligible global warming potential, is required in quantities for application in plasma dielectric etching in
semiconductor industry and as gaseous microbubble suspension contrast agents in diagnostic ultrasound imaging. Three efficient protocols for the
preparation of perfluoro-1,3-butadiene in 62–70% overall yields have been described. They involve the coupling of (1) iodotrifluoroethylene
(
ITFE) with activated copper, (2) trifluorovinylzinc bromide in the presence of copper (II) or iron (III) salts and (3) trifluorovinylzinc chloride,
prepared from 1,1,1,2-tetrafluorethane (HFC 134a) in the presence of copper (II) or iron (III) salts.
2008 Published by Elsevier B.V.
#
Keywords: Etching-gases; Ultrasound contrast agents; Gaseous microbubbles; Hexafluoro-1,3-butadiene; Coupling reaction; Bromortrifluoroethylene
1
. Introduction
derivative was achieved using zinc in ethanol (Scheme 1) [5]. A
modified synthesis of 1 from the disodium salt of octafluor-
ohexane-1,6-dioic acid via decarboxylation and defluorination
was also reported by Haszeldine (Scheme 2) [6]. Dedek and
Chvatal [7] developed a cumbersome process for the
preparation of 1 by the initial addition of 1,2-dibromo-1-
chlorotrifluoroethane to chlorotrifluoroethylene under ultra-
violet radiation to obtain a mixture of products, including 1,4-
dibromo-2,3-dichlorohexafluorobutane (Scheme 3). This was
isolated and treated with zinc and ethanol to provide 1. Copper
and iron-mediated coupling of perfluoroalkenyl iodides and
bromides are known [8]. During an attempted preparation
of trifluorovinylcopper reagent from iodotrifluoroethylene
(ITFE), Burton and Hansen [9] recognized its dimerization
[10].
Fluoroorganic molecules have found applications as phar-
maceuticals, agrochemicals, and valuable materials in electro-
nics industry [1]. Noteworthy examples of the latter application
are gaseous fluorocarbons utilized for plasma dielectric
etching. Of the several dry-etching-gases, hexafluoro-1,3-
butadiene (C F , 1) with Xe and Ar as carrier gas is preferred
due to its negligible global warming potential (GWP) [2,3].
Chatterjee et al. have reported an 80% decrease in global
warming plasma emissions from a C F -based etching process
4
6
4
6
compared to C F etching process [3]. This material has a very
3
8
short atmospheric lifetime, decomposing within 2 days.
Perfluorocarbon gases, including C4F6 have recently been
exploited to generate stable gaseous microbubble suspensions
as ultrasonic contrast agents in diagnostic molecular imaging
Due to the industrial importance of 1, there are a few recent
protocols described in patent literature for its preparation
[11–13]. Two of these involve the preparation of 1 via the
dehalogenation of 1,4-dihalooctafluorobutadiene and the third
patent [13] describes the preparation of 1 from 1,2-dibro-
motetrafluoroethane via isomerization, dehalogenation and
dimerization using cupric bromide.
[
4].
Haszeldine and co-workers reported the first synthesis of 1
more than half a century ago from chlorotrifluoroethylene
CTFE), via the corresponding 1,2,3,4-tetrahalogenobutane,
(
prepared by the treatment with iodine monochloride or
monobromide, followed by reacting with mercury in UV
light or zinc in dioxane. The dehalogenation of the tetrahalo
As part of our program in fluoroorganic chemistry, we were
interested in developing a simple cost-effective synthesis of 1
from bromotrifluoroethylene for large-scale applications.
Following are the details of our study on the preparative-scale
synthesis of hexafluoro-1,3-butadiene.
*
Corresponding author. Tel.: +1 765 494 5303; fax: +1 765 494 0239.
E-mail address: chandran@purdue.edu (P.V. Ramachandran).
0022-1139/$ – see front matter # 2008 Published by Elsevier B.V.
doi:10.1016/j.jfluchem.2008.01.015

444
P.V. Ramachandran, G.V. Reddy / Journal of Fluorine Chemistry 129 (2008) 443–446
Scheme 1.
2
. Results and discussion
We undertook a systematic study to realize a one-pot
synthesis of 1 that can be scaled up. Initially, our focus was on
the transition metal-catalyzed coupling of the haloolefins. To
this end, we attempted a Negishi coupling [14] of trifluor-
ovinylzinc bromide with BTFE in the presence of palladium
chloride. However, no formation of 1 was observed (Eq. (1)).
We utilized other palladium salts, such as palladium acetate and
nickel salts, such as nickel chloride to no avail. Since vinyl
iodides serve as better coupling partners, ITFE was prepared
from BTFE using zinc and iodine. Similar attempts to couple
ITFE using palladium and nickel salt catalysts also failed to
provide 1. We then sought to dimerize ITFE in the presence of
activated copper powder in dimethylformamide (DMF), on the
basis of the observation of Burton et al. [8], and achieved the
coupled product in 67% isolated yield (Eq. (2)).
Scheme 3.
Table 1
Preparation of hexafluoro-1,3-butadiene from trifluoroethylenezinc halides
a
Entry
TFEZnX X
Metal salt
4 6
C F yield (%)
1
2
3
4
5
6
7
Cl
Cl
Br
Br
Br
Br
Br
CuBr
FeCl3
2
69
68
68
68
62
68
70
CuBr
2
Cu(OAc)
2
Cu(OTf)
FeBr
FeCl
2
3
(1)
3
a
Reaction condition: metal salt (0.03 mol) was added to TFEZnX (0.03 mol)
in DMF (50 mL) at RT and hexafluoro-1,3-butadiene was collected simulta-
neously at À78 8C.
1 was realized in 62–70% isolated yields and 100% chemical
purity in all of the cases (Eq. (3)).
(2)
(3)
We then attempted a cost-effective synthesis of 1 from the
corresponding trifluorovinylzinc chloride utilizing a simple
preparation from 1,1,1,2-tetrafluoroethane (HFC-134a) [15].
The dimerization was attempted in the presence of Cu(II) or
Fe(III) salts, as in the case of Eq. (3). Much to our satisfaction,
we achieved the preparation of 1 in 69–70% yield (Eq. (4)). The
results are summarized in Table 1.
Encouraged by this result, we directed our efforts towards an
efficient synthesis of 1 from BTFE, avoiding the preparation of
ITFE. Screening of several metal salts, solvents, and
temperature were performed for arriving at the optimal
conditions for the desired dimerization. Indeed, our goal was
achieved in the presence of copper (II) salts, such as copper
acetate, bromide, or triflate and iron (III) salts, such as ferric
chloride or bromide, in DMF as solvent. The dimerized product
(
4)
3. Conclusion
In summary, we have developed a simple, practical and high
yielding procedure for a one-pot preparation of hexafluor-
Scheme 2.

P.V. Ramachandran, G.V. Reddy / Journal of Fluorine Chemistry 129 (2008) 443–446
445
obutadiene by the coupling of iodotrifluoroethylene in the
presence of activated copper or from bromotrifluoroethylene or
ꢀ70 8C, which was controlled by keeping the RB flask in
ice-water. The reaction mixture turned brown and was stirred
further for 1 h at RT, completing the formation of the
trifluorovinylzinc bromide.
1
,1,1,2-tetrafluoroethane via the coupling of the trifluorovi-
nylzinc halides (chloride or bromide), in the presence of copper
II) or iron (III) salts. All of these procedures were repeated
(
The flask was now fitted with an addition funnel and while
the reaction mixture is cooled to 0–5 8C, and applying vacuum
using a water aspirator pump (100 mm Hg), 33 mmol of ferric
salt (FeCl or FeBr ) or cupric salt (Cu(OTf) or Cu(OAc) ) was
several times and reproduced. These protocols are amenable to
scaling up and the yields can be improved by carrying out the
reactions in well-sealed conditions [16]. The negligible global
warming potential of C4F6 with the required process
performance, an efficient alternative to CF , CHF , and
3
3
2
2
added slowly, maintaining the reaction temperature below 5 8C.
FeCl is soluble in DMF and can be added as a solution. Most of
4
3
3
C F , should make this procedure attractive.
4
hexafluorobutadiene was collected in a trap cooled using dry
ice-acetone (À78 8C). The rest of the product was collected by
warming the reaction to 40 8C and stirring for 2 h (all the while
applying vacuum). The reaction was repeated several times and
the yield of the reactions ranges between 62–70% (see Table 1).
8
4
. Experimental
Bromotrifluoropropene and HFC-134a were obtained as a
gift from Great Lakes Chemical Corporation (Chemtura). All
other chemicals were purchased from various commercial
4
.1.3. From HFC-134a
Under nitrogen, to a 100 mL RB flask having side-arm and
1
9
sources. The F (CFCl3 or trifluoroacetic acid internal
standard) nuclear magnetic resonance (NMR) spectrum was
plotted in CDCl3 on a Varian Gemini-300 spectrometer
fitted with dry ice condenser, 4.2 g (32 mmol) of anhydrous
zinc chloride, 30 mL of dry THF were added. The suspension
was cooled to 10 8C and HFC-134a (36 mmol) was added
slowly. LDA (64 mmol) (lithium diisopropyl amine 1.8 M
solution) is added slowly through a syringe to the above HFC-
(
282 MHz) with a Nalorac-quad probe.
The Zinc dust used for the reactions was activated [17] by
stirring 100 g of zinc powder with 50 mL of 10% dilute
hydrochloric acid for 2–4 min, filtering and washing with
134a/ZnCl slurry, while maintaining the temperature <15 8C.
2
(The tip of the needle was dipped into THF to avoid
1
00 mL of water, followed by 50 mL of acetone and drying in
decomposition of trifluovinyllithium formed by reaction of
HFC-134a with LDA). The reaction mixture was stirred for 1 h
and allowed to warm to room temperature. After that reaction
mixture was cooled to 0–5 8C, and applying vacuum (100 mm
oven (130–140 8C) for 1 h.
The copper powder used for the reactions was activated as
follows [18]. 20 g of copper powder was treated with 200 mL of
2
% solution of iodine in acetone for 10 min. This resulted in the
Hg), 33 mmol of ferric salt (FeCl or FeBr ) or cupric salt
(Copper triflate or Cu(OAc) ) was added slowly, maintaining
formation of a rather grayish color due to the formation of
copper iodide. The activated copper was filtered and washed
with 100 mL of 1:1 solution of conc. HCl in acetone. The
copper iodide gets dissolved and the residual copper is filtered,
washed with acetone, and dried under vacuum at 40–50 8C for
immediate in the next step.
3
3
2
the reaction temperature below 5 8C. The reaction was stirred at
0 8C for 2 h and the product collected using a trap cooled at
4
À78 8C. The reaction was repeated several times to confirm the
yields (68–69%, Table 1).
Acknowledgements
4
4
5
.1. Preparation of hexafluoro-1,3-butadiene
We gratefully acknowledge Chemtura for financial support
and the gift of BTFE and HFC-134a for this research.
.1.1. From iodotrifluoroethylene
Activated copper powder (8.5 g, 132 mmol) was placed in
0 mL of dry DMF in a 100 mL RB flask having a side arm
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(
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