An efficient synthesis of 1-chloro-2,2-difluoroethylene via the reductive dechlorination of 1,2,2-trichloro-1,1-difluoroethane

Article abstract of DOI:10.3184/096034013X13644802548720

1-Chloro-2,2-difluoroethylene was prepared from 1,2,2-trichloro-1,1- difluoroethane by reductive dechlorination in the presence of zero-valent zinc. Eleven different solvents were investigated and the best results were obtained in methanol, dimethyl formamide and ethanol at 80 °C. A large-scale experiment using ethanol as a solvent gave 1-chloro-2,2-difluoroethylene in high yield. These results provide a method for producing 1-chloro-2,2- difluoroethylen e on an industrial scale because 1,2,2-trichloro-1,1- difluoroethane is the waste material arising from 2,2-dichloro-1,1,1- trifluoroethane production. These results can also provide a method for solving the recycling problem of 1,2,2- trichloro-1,1-difluoroethane in 2,2-dichloro-1,1,1-trifluoroethane production.

Full text of DOI:10.3184/096034013X13644802548720

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JOURNAL OF CHEMICAL RESEARCH 2013
RESEARCH PAPER 273
MAY, 273–275
An efficient synthesis of 1-chloro-2,2-difluoroethylene via the reductive
dechlorination of 1,2,2-trichloro-1,1-difluoroethane
Nong Wanga,b*, Lijuan Yanga and Shaoji Xiangc
aSchool of Chemical and Biological Engineering, Lanzhou Jiaotong University, Lanzhou 730070, P. R. China
bEngineering andTechnology Center of Gansu Province for Botanical Pesticides, Lanzhou Jiaotong University, Lanzhou 730070, P. R. China
cZhejiang Chemical Industry Research Institute, 378Tianmushan road, Hangzhou, Zhejiang 310023, P. R. China
1-Chloro-2,2-difluoroethylene was prepared from 1,2,2-trichloro-1,1-difluoroethane by reductive dechlorination in
the presence of zero-valent zinc. Eleven different solvents were investigated and the best results were obtained in
methanol, dimethyl formamide and ethanol at 80 °C. A large-scale experiment using ethanol as a solvent gave
1-chloro-2,2-difluoroethyleneinhighyield.Theseresultsprovideamethodforproducing1-chloro-2,2-difluoroethylene
on an industrial scale because 1,2,2-trichloro-1,1-difluoroethane is the waste material arising from 2,2-dichloro-1,1,1-
trifluoroethane production. These results can also provide a method for solving the recycling problem of 1,2,2-
trichloro-1,1-difluoroethane in 2,2-dichloro-1,1,1-trifluoroethane production.
Keywords green chemistry, 1-chloro-2,2-difluoroethylene, reductive dechlorination, industrial production
1-Chloro-2,2-difluoroethylene is a raw material1 and key
intermediate for the production of fluorine-containing textile
finishing agents, fluorosurfactants, organic silicon fluorine
modified resins and other fluorine containing fine chemicals.2,3
These products can be used as heat exchange materials, refrig-
erants, foaming agents, solvents, cleaning agents, polymerisa-
tion media, polyolefin and polyurethane expansion agents, gas
dielectrics and flame retardants.4
2,2-Dichloro-1,1,1-trifluoroethane is a new type of foaming
agent, which is also used as a refrigerant and cleaning agent.
Because it has only 0.02 of ozone destruction potential (ODP)
and other good properties, it is becoming better known as a
replacement for Freon and Halon.5,6 It also has potential appli-
cation in the production of fluorine containing medicines and
pesticide intermediates.7 Many companies have successfully
set up 2,2-dichloro-1,1,1-trifluoroethane plants. For example,
Sinochem Lantian Co., Ltd has the largest single set of produc-
tion capacity (10000 tons/year) in the world at present. The
conventional manufacturing process for 2,2-dichloro-1,1,1-tri-
fluoroethane is shown in Scheme 1. The overall process is
divided into two steps. Firstly, trichloroethylene is reacted
with hydrogen fluoride forming 2-chloro-1,1,1-trifluoroethane
which is then converted in a second step to 2,2-dichloro-1,1,1-
trifluoroethane.
In the first step, dehydrohalogenation is suppressed in the
presence of hydrogen fluoride. The second stage is a fast reac-
tive free-radical with a poor selectivity,8 giving side reactions.9
Besides the target product 2,2-dichloro-1,1,1-trifluoroethane,
the gaseous mixture also contains 1,2,2-trichloro-1,1-difluoro-
ethane which is the by-product of a 1,2-dichloro-1,1-difluoro-
ethane chlorination, shown in Eqn (3) of Scheme 2. It may also
be a by-product of the addition of hydrogen chloride to 1,1-
dichloro-2,2-difluoroethene. 1,1-Dichloro-2,2-difluoroethene
is obtained from 2,2-dichloro-1,1,1-trifluoroethane by the
elimination of hydrogen fluoride. These proposed reactions
are shown in Eqn (4) of Scheme 2.
According to a recent survey, the annual production of
10,000 tons of 2,2-dichloro-1,1,1-trifluoroethane, can lead to
about 50 tons of 1,2,2-trichloro-1,1-difluoroethane. This
has not been utilised efficiently. Burning, which is currently
used, is also a tremendous waste of resources. Therefore, the
purpose of our study was to solve the recycling problem of
1,2,2-trichloro-1,1-difluoroethane formed during 2,2-dichloro-
1,1,1-trifluoroethane production. At present, we have mainly
transformed 1,2,2-trichloro-1,1-difluoroethane into the more
valuable 1-chloro-2,2-difluoroethylene, by a simple, reliable
process to give a product with good stability, selectively and in
high yield.
The present methods of producing 1-chloro-2,2-difluoroeth-
ylene can be divided into two groups.
(1) Using 1,2,2-trichloro-1,1-difluoroethane as raw material
for preparing 1-chloro-2,2-difluoroethylene:
A catalytic method was reported by Vanlautem et al.10 who
used active carbon as the carrier, copper and precious metals of
group VIIIB such as Pt to make Cu–Pt binary metal hydro-
genation–dechlorination catalyst for preparing 1-chloro-2,2-
difluoroethylene from 1,2,2-trichloro-1,1-difluoroethane. This
catalytic synthesis was carried out under high temperature
and high pressure. Specifically, the hydrogen pressure was 1.0
MPa and reaction temperature was 240 °C as shown in Scheme
3. The cost of producing 1-chloro-2,2-difluoroethylene is high
because the catalysts used in this technology comprised VIIIB
group precious metal elements. The chlorine atoms within
the raw materials were partly reduced by hydrogen atoms
and gave impurities such as 1, 1-dichloro-2,2-difluoroethane,
1-chloro-2,2-difluoroethane and 1,1-difluoroethane. This
affected the yield of the reaction, and made the products
difficult to purify.
(2) Using 1-bromo-1-chloro-2,2,2-trifluoroethane as raw
material for preparing 1-chloro-2,2-difluoroethylene:
Hudlicky and Lejhancova have reported a method for pro-
ducing 1-chloro-2,2-difluoroethylene from 1-bromo-1-chloro-
2, 2, 2-trifluoroethane11 by using zinc powder as a reductant in
Scheme 1
* Correspondent. E-mail: wangnong07@163.com
Scheme 2

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274 JOURNAL OF CHEMICAL RESEARCH 2013
reactions, after backflow for an hour, the yield was about 70%
(Scheme 6).
Experimental
The 19F NMR spectra were recorded on a Varian 400MHz spectrom-
1
eter. The chemical shifts were referenced to TMS for H NMR and
Scheme 3
CFCl3 for 19F NMR respectively. Gas chromatography was as follows:
gas chromatograph GC-2010, (Shimadzu) Qualitative analysis used
GC-MS Voyager mass spectrometer_Trace 2000.
1,4-dioxane at temperature of 100 °C, 1-chloro-2,2-difluoro-
ethylene was obtained after reaction for 2 hours in a yield of
reaction was 71% as shown in Scheme 4.
All solvents were dried with a molecular sieve and were of analyti-
cal grade, and the zinc powder (325 mesh)was pretreated before use
by literature procedures.16,17
The main problem of this technology is the shortage of
raw material 1-bromo-1-chloro-2, 2, 2-trifluoroethane. Hence
this synthetic route is not suitable for large scale industrial
production.
Thus, the two present methods for preparing 1-chloro-2,2-
difluoroethylene have a series of problems: the high price of
raw materials and catalysts, the low yield, and the large organic
solvent consumption. The cost of production is high. These
reactions are hard to convert to the industrial production of
1-chloro-2,2-difluoroethylene. Therefore, it is necessary to
explore an industrial process leading to 1-chloro-2,2-difluoro-
ethylene.
Small-scale preparation of 1-chloro-2,2-difluorothylene
Powdered zinc (0.13g, 2.0 mmol) was added to a 50 mL upright flask.
After evacuating the flask, the solvent (1 mL) was injected into the
flask using a syringe. The mixture was heated to 80 °C (or 120 °C)
with magnetic stirrer, and 1,2,2-trichloro-1,1-difluoroethane 0.167 g
(1.0 mmol) was added using a syringe. The reaction was followed
by GC and 19F NMR. 1-Chloro-2,2-difluoroethylene was obtained as
a colorless gas.
Spectroscopic data for 1-chloro-2,2-difluoroethylene: MS (Mr =
98.1), m/z (% relative intensity), EI: 48.2(43), 50.2(23), 63.2(49),
67.1(23), 69.1(8), 79.1(22), 81.1(8),98.1(100), 100.1(78). H NMR
1
(400 MHz, CDCl3): δ 5.295(dd, J1 = 17.2 Hz, J2 = 1.2 Hz)ppm.
19F NMR (376.4 MHz, CDCl3): δ –86.836 (dd, JHF = 19.2 Hz, JHF
42.7 Hz), –91.084 (d, JHF = 42.9 Hz)ppm.
=
There are existing methods using zinc powder as a reducing
agent for preparing similar fluoroalkenes by reductive dechlo-
rination:
Large-scale preparation of 1-chloro-2,2-difluorothylene
Edward et al. prepared 1,1-dichlone-2,2-difluoroethylene
from 1,1,1,2-tetrachloro-2,2-difluoroethane using zinc powder
in methanol for a reductive dechlorination reaction at a tem-
perature of 60–63 °C.12 Sauer optimized and improved this
method,13 and by adding small amounts of zinc chloride in
the initial stage of the reaction increased the reaction yield to
89–95% (Scheme 5).
Ethanol (3135 mL) and 1,2,2-trichloro-1,1-difluoroethane (2099g)
was mixed. The pretreated Zinc powder (325 mesh) was added
in batches to a 5L three-necked flask at 80 °C. After all the starting
material had been added, it was refluxed for another 2 hours and the
1-chloro-2,2-difluoroethylene was collected by –60 ~ –80 °C freezing
circular ethanol, 1127g crude product was obtained, the GC content
is as high as 95% of 1-chloro-2,2-difluoroethylene with a yield of
92.3%.
Maynard et al.14,15 used zinc as a reducing agent in ethanol
to prepare 1-chloro-2,3,3-trifluorocyclobutene from 1,1,2-tri-
chloro-2,3,3-trifluorocyclobutane by reductive dechlorination
Results and discussion
The synthetic reaction is shown in Scheme 7. We have investi-
gated the reactions of 1,2,2-trichloro-1,1-difluoroethane in
a series of solvents at temperatures of 80–120 °C. The GC
data and 19F NMR data of the liquid phases of the reaction are
summarised in Tables 1 and 2, respectively.
Our experimental results show that the reactions with MeOH
and DMF as solvent gave selectively 1-chloro-2,2-difluoroeth-
ylene in good yield (Table 1). There was almost no reaction in
Scheme 4
Scheme 5
Scheme 6
Scheme 7

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JOURNAL OF CHEMICAL RESEARCH 2013 275
Table 1 Gas phase content of reaction mixtures
cheaper and safer than any other solvents and it is environmen-
tally friendly, the scale-up experiment used ethanol as a
solvent.
Sol.
R1122/%
R122/% Impuritya
T/°C
MeOH
EtOH
98.4
95.6
97.6
91.1
75.1
92.2
0.23
1.30
0.37
0.85
0.18
0.90
0
0
1
2
3
1
80
80
80
80
80
80
Conclusion
THF
In conclusion, 1-chloro-2,2-difluoroethylene has been synthe-
sised from 1,2,2-trichloro-1,1-difluoroethane which was a
by-product from the waste material of 2,2-dichloro-1,1,1-tri-
fluoroethane production process. The reductive dechlorina-
tions of 1,2,2-trichloro-1,1-difluoroethane by zinc in eleven
different solvents was investigated, and the reactions in MeOH
and DMF as solvent had good stability and gave 1-chloro-2,2-
difluoroethylene in high yield. The scale-up experiments using
ethanol as a solvent also gave a good yield. These results
provide a method for producing 1-chloro-2,2-difluoroethylene
and to solve the recycling problems of 1,2,2-trichloro-1,1-
difluoroethane derived from 2,2-dichloro-1,1,1-trifluoroethane
production, compatible with industrial methodology.
CH3CN
DME
Dioxane
0
86.2
4
80
Morpholine
DMF
37.4
98.4
52.1
96.8
1.94
0.04
7
0
3
1
80
80
80
80
D.G.
29.6
DMAC
1.89
74.0
0.49
4
120
D.G.
DMAC
94.7
94.9
1.07
0.60
1
2
120
120
a Impurities representing more than 1% by area of the GC
(R1122:1-chloro-2,2-difluoroethylene, R122: 1,2,2-trichloro-1,1-
difluoroethane).
This work was supported by the Major Science and Technol-
ogy Projects of Gansu (Grant No. 1002NKDA025), the
Engineering and Technology Center Projects of Gansu (Grant
No. 1106NTGA013) and ‘Qing Lan’Talent Engineering Funds
of Lanzhou Jiaotong University.
Table 2 19F NMR data of reaction liquid phase mixtures
Sol.
R1122/R122
Impurity/ppma
Received 25 January 2013; accepted 21 February 2013
Paper 1301751 doi: 10.3184/096034013X13644802548720
Published online: 15 May 2013
MeOH
EtOH
100/433
100/400
100/823
100/168
100/83
0/136
–
–
–
–
–
–
THF
CH3CN
DME
Dioxane
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