A novel and efficient synthetic route to perfluoroisobutyronitrile from perfluoroisobutyryl acid

Article abstract of DOI:10.1039/C8RA07821A

A novel synthetic route to perfluoroisobutyronitrile from perfluoroisobutyryl acid which has mild conditions and low toxicity is described. This study introduces detailed synthetic protocols and characterization including GC-MS, ¹³C NMR and ¹⁹F NMR spectroscopy of perfluoroisobutyryl acid, perfluoroisobutyryl chloride, perfluoroisobutyl amide and perfluoroisobutyronitrile. Besides, this route is superior to the established patent and shows potential application in high voltage electrical equipment.

Full text of DOI:10.1039/C8RA07821A

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A novel and efficient synthetic route to
perfluoroisobutyronitrile from perfluoroisobutyryl
acid†
Cite this: RSC Adv., 2018, 8, 37159
Yi Wang, Mengting Sun, Zhanyang Gao, Lilin Zou, Lingyu Zhong, Ruichao Peng,
*
Ping Yu and Yunbai Luo
A novel synthetic route to perfluoroisobutyronitrile from perfluoroisobutyryl acid which has mild conditions
and low toxicity is described. This study introduces detailed synthetic protocols and characterization
including GC-MS, 13C NMR and 19F NMR spectroscopy of perfluoroisobutyryl acid, perfluoroisobutyryl
chloride, perfluoroisobutyl amide and perfluoroisobutyronitrile. Besides, this route is superior to the
established patent and shows potential application in high voltage electrical equipment.
Received 21st September 2018
Accepted 29th October 2018
DOI: 10.1039/c8ra07821a
rsc.li/rsc-advances
Recently, GE has built a 420 kV i-C4F7N/CO2 GIL. 3 M (Min-
nesota, Mining and Manufacturing) has issued a patent on the
synthetic route to i-C4F7N (Scheme 1a).12 According to their
protocol, methyl peruoroisobutyrate was used as the initial
starting material which was made to react with NH3 to form
peruoroisobutyl amide. The dehydration of the per-
uoroisobutyl amide resulted in the formation of per-
uoroisobutyronitrile. The dehydration of peruoroisobutyl
amide to produce its corresponding nitrile is an established
synthetic strategy.
Sureshbabu had reported the general protocol for the
synthesis of Boc-amino nitriles (Scheme 1b).13 The method was
also found to be suitable for the synthesis of
peruoroisobutyronitrile.
Earlier attempts by Ishikawa to prepare organometallic
compounds from peruoroalkyl iodides and carbon dioxide
yielded peruoroalkyl acid as the organic product.14 Ishikawa
had explained the mechanism for the formation of per-
uoroalkyl acid and reported the 19F NMR of a series of per-
uoroalkyl acids. However, the 19F NMR data of C3F7COOH had
certain inaccuracies. Ishikawa had taken C8F17COOH as an
example, and explained the detailed procedure of its prepara-
tion. Even so, the physical properties of C3F7COOH and
Introduction
The gaseous compound sulfur hexauoride (SF6) has a high
dielectric strength (DS) and a good arc extinguishing perfor-
mance. These features allow it to be widely used as a main-
stream insulating gas which was previously used in GIS (Gas
Insulated Switchgear), GIL (Gas Insulated Lines) or other large
power equipment. However, it is also extremely harmful to the
environment and the atmosphere because it takes a long time to
decompose when it has been in the air. The GWP (Global
Warming Potential) of SF6 is around 23 000 times that of CO2. It
is expected to result in a stronger greenhouse effect.
The Kyoto Protocol, the supplement of the United Nations
Framework Convention on Climate Change has declared SF6 as
one of the six limiting gases. In order to overcome this issue,
participating countries are urgently striving to nd a new
alternative compound with a low GWP as well as high DS that
can completely replace SF6.1–3
On-going research in General Electric (GE), America has led
to the emergence of some new insulating gases like CF3I, c-C4F8,
i-C5F10O, and i-C4F7N. There are handful reports about the
synthesis of i-C4F7N, furthermore most of them aren't practical
to apply in industry.4–11 The gas i-C4F7N, when mixed with CO2,
exhibits excellent properties, which surely be one of the rst
choices to replace SF6. Besides, the GWP of i-C4F7N is only 2210,
which is far lower than that of SF6. Under the same pressure,
insulation strength and arc extinguishing performance of i-
C4F7N/CO2 can reach 90% or higher than that of SF6.
Engineering Research Center of Organosilicon Compounds & Materials, Ministry of
Education, College of Chemistry and Molecular Sciences, Wuhan University, Wuhan,
430072, P. R. China. E-mail: ybai@whu.edu.cn
† Electronic supplementary information (ESI) available: Additional results of
various conditions, GC-MS, 13C NMR and 19F NMR data and spectra provided.
See DOI: 10.1039/c8ra07821a
Scheme 1 (a) The patent of 3 M; (b) synthesis of Boc-amino nitriles.
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C8F17COOH such as the boiling point or melting point are very
different. In fact, it was difficult to obtain peruoroisobutyryl
acid following the general procedures given by Ishikawa.
To the best of our knowledge, only a handful of reports are
available regarding the synthesis of peruoroisobutyryl acid.
One of the prime reasons behind this is the most of the
researchers focused on the formation of peruoroisopropylzinc
iodide, but actually the concentration of CO2 also performed an
important factor in the reaction. The scenario here is somewhat
different from other organometallic reactions. We had even
tried to purchase peruoroisobutyryl acid from some commer-
cial chemical companies, but interestingly, none of them were
successful in synthesizing it, in spite of following the reported
protocols. The other reason for this compound being so less
studied is the fact that only a little was known about its practical
value previously. However, considering Kyoto Protocol, per-
uoroisobutyronitrile has a widespread application in GIL and
other large-scale electrical equipment. Hence, it is highly likely
for peruoroisobutyryl acid to become a new raw material for
the preparation of peruoroisobutyronitrile.
Fig. 1 Synthesis of 1 from perfluoroisopropyl iodide.
So far, no study exists which reports the synthesis of per-
uoroisobutyronitrile from peruoroisobutyryl acid. Besides,
there are no reports on the properties of peruoroisobutyryl
chloride. This study would be the rst of its kind to report the
details.
methods to prepare 1 (detail data and results of various
conditions were shown in ESI†) and listed their conditions and
yield.
For this reaction, carbon dioxide was found to react with zinc
compounds only under ultrasound and high pressure which is
1 MPa or higher. Increasing the concentration of CO2 in the
system determined the success of the step. Ultrasonic condition
or high pressure has been proved to be indispensable, as the
desired product could not be obtained under normal pressure
without ultrasound or high pressure. Nevertheless, when the
solution and dry ice were placed in a closed cylinder with
a pressure of 1 MPa or higher, the formation of per-
uorocarboxylic acid salt was observed. The summarized
results were shown in Table 1.
Results and discussion
Our attention was drawn to a novel synthetic route to i-C4F7N
from a safer raw material where peruoroisobutyryl acid was
initially converted to the corresponding chloride which was
a highly reactive intermediate (Scheme 2). The synthetic route to
peruoroisobutyryl acid (1) was shown in Fig. 1. In our work, the
peruoroisopropyl iodide was found to react readily with zinc
powder and carbon dioxide in an aprotic solvent under an
ultrasound condition. In additions the reaction could also take
place under high pressure. In this study, we had used the two
Peruoroisopropyl iodide was found to react readily with
zinc powder in solution to form peruoroisopropyzinc iodide,
Table 1 The results of various pressure to synthesize 1a
Entry
Pressureb (MPa)
Yieldc (%)
d
1
2
3
4
0
1
2
3
—
24
33
69
a
Reaction conditions: peruoroisopropyl iodide (0.1 mol) in 30 mL
DMF was added into 40 mL DMF including Zn powder at 50 ꢀC for
b
2 h. Relative pressure in the reactor. The maximum pressure of
reactor is 3 MPa. Isolated yield. Yields were determined by 19F NMR
c
d
analysis using triuorotoluene as an internal standard. No expected
product was obtained.
Scheme 2 The synthetic route in this study.
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which further reacted with carbon dioxide under ultrasound or hexauoropropylene (HFP) in the distillation step.17 This would
high pressure to give a nal yield of nearly 70% 1. It was found ultimately reduce the quantity of 1. In contrast, if the temper-
ꢀ
that the synthesis at the reux temperature was easier when the ature exceeded 70 C or higher, most of raw materials was lost
halide atom was iodide rather than bromide. On the other during the reaction. Furthermore, the solution could not
hand, the thermal stability of peruoroisopropylzinc iodide in maintain the required concentration of carbon dioxide, as
solution was in striking contrast to the instability by per- a result of which high conversion rates could not be obtained.
uoroisopropyzinc bromide.15
In addition, the stability of the peruorocarboxylic acid metal
The amount of metal powder used in the reaction ranged salt decreases at higher temperatures. Therefore, it was neces-
from 1 to 4 equivalents of the raw material. It is evident that the sary to nd an optimum temperature that could avoid thermal
yield of the reaction reached a plateau when the amount of the decarboxylation an effect that was accentuated by the decom-
metal reached to more than 4 equivalents of the halogen in the position to form HFP or dimers and trimers irreversibly.
raw material. Besides, the excessive metal powder in the solu-
Ultrasound has been already proven to be an essential
tion rendered the separation step more difficult. In contrast, if requirement for the combination of carbon dioxide and metal
the amount of the metal was less than 1 equivalent, the nal compounds in promoting the reaction because ultrasound
solution was found to have a substantial amount of the starting forms cavities that can readily dissolve carbon dioxide in solu-
material, since the metal powder was not enough to react with tion. The pressure was also found to be an important factor in
the entire reactant. In order to maximize the rate of conversion, this study. It was found that the reaction could take place even
and reduce the complexities during the separation, the most without ultrasound, if the pressure was greater than 1 MPa. This
suitable amount should be 3 equivalents of the raw material. observation could be justied on the basis of the fact that high
The zinc powder (diameter ranged from 1–3 mm) should be pressures could reasonably increase the concentration of
fully activated by 1 mol Lꢁ1 HCl (aq) and washed by acetone and carbon dioxide in the solution. Either way, both the methods
ethanol. Then it was stored in the dry vacuum case until to be aimed at increasing the dissolution of the carbon dioxide in the
used.
Aprotic solvents such as N,N-dimethylformamide (DMF),
solution.
The peruoroisobutyrylzinc compound was so stable that it
tetrahydrofuran (THF), or diethyl ether used have been studied. could be stored at room temperature with hardly any other
ꢀ
DMF was found to be a convenient solvent because it could be reactions occurring. However, heating over 100 C initiated its
hydrolyzed directly by water. Diethyl ether has an added decomposition to form HFP. Hydrolysis of per-
advantage because its boiling point is lower than per- uoroisobutyrylzinc proceeded rapidly with the addition of
uoroisopropyl iodide.16 As a result, no remarkable amount of water at room temperature. The products included Zn(OH)I and
peruoroisopropyl iodide was lost at the reux temperature. 1,1,1,2,3,3,3-heptauoropropane (C3F7HF). C3F7HF was a gas
Owing to the high saturation vapor pressure of diethyl ether, the phase at room temperature while the Zn(OH)I formed a precip-
combination of the solution and carbon dioxide became diffi- itate in the sodium hydroxide solution. The precipitate of
cult. When using THF as the solvent, we found that per- Zn(OH)I disappeared when then pH of the solution was made
uoroisopropyl iodide could not be dissolved in it. The acidic. The reaction of peruoroisobutyrylzinc compound with
purication of the solvent by molecular sieve was benecial for CO2 could take place under ultrasound or high pressure to form
the reaction. Direct use of anhydrous solvent was also a conve- uoroisobutyryl acid salt. The salt was converted into 1 aer the
nient method and gave satisfactory results.
addition of hydrochloric acid in order to adjust the pH to be less
The concentration of raw material in the solvent ranged from than 2. The nal pure 1 was obtained aer being separated,
1 mol Lꢁ1 to 3 mol Lꢁ1. The solvent-free method seems to be dried and distilled.
unsuitable because of the instability of peruoroisopropyl
The choice of solvent in the step concerning the synthesis of
iodide which evaporates quickly under ultrasound or high 2 was versatile. The solvents used could be DMF or THF, and
pressure due to the generation of heat. This would obviously interestingly (Table 2), the reaction could also progress without
result in the loss of a massive amount of raw material, thereby the presence of any solvent. Different solvent showed different
lowering the yield. If a very high quantity of the solvent is used, results. For example, DMF was found to catalyze this particular
the concentration of raw material will become less than synthesis. Addition of high amounts of DMF made the reaction
1 mol Lꢁ1, which is not desirable. A high quantity of the solvent more vigorous. If THF was used as solvent, the vapour pressure
would also require a larger quantity of hydrochloric acid in the of the solvent needed to be considered. This is because THF
next step while lowering of the pH to enable the acidication of would be present even in the distillate, although it could be
the peruorocarboxylic acid salt.
removed in next step of synthesizing the peruoroisobutyl
We found that the most suitable reaction temperature was amide (3). The possible reason is that the boiling point of THF is
60 ꢀC. In order to prove the most suitable temperature, we lower than that of the amide. The absence of any solvent was
carried out the reaction over a temperature gradient. The cor- acceptable. But storing the puried product would be difficult
responding results are summarized in ESI.† The result illus- due to the vapour pressure and low boiling point.
trated that the reaction could not take place at low
The synthesis of 2 didn't take place at low temperature.
temperatures. The main impurity was found to be the raw Contrarily, the high temperature was also not favorable for the
material itself when the temperature was below 60 ꢀC. Below reaction because of the low boiling point and high vapor pres-
60 ꢀC, most of the
1
will decompose to form sure of 2. So the most suitable temperature was determined to
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Table 2 The result of various solvent to synthesize 2a
Scheme 3 Synthesis of methyl perfluoroisobutyrate.19
Solvent
Purityb (%)
Yieldc (%)
purication, unless otherwise stated. Ultrasonication was per-
formed on a GT SONIC-P3 ultrasonic apparatus. Y2UR-250 type
high-pressure reactor used in this study was purchased from
ShangHai YanZheng Instrument Co. Ltd.
NMR spectra of 1 and 2 were recorded on a Bruker Avance-III
NMR spectrometer (1H: 400 MHz, 19F: 376 MHz, 13C: 100 MHz)
with reference to an internal (1H, 13C: SiMe4) and an external
standard (19F: CDCl3).
d
DCM
DMF
THF
No solvent
—
52
31
99
—
6
61
60
a
Reaction conditions: 1 (0.05 mol), oxalyl chloride (0.055 mol) in
b
c
d
solvent (3 equiv) at 50 ꢀC for 2 h. GC purity. Isolated yields. No
expected product was obtained.
NMR spectra of 3 and C4 were recorded on at temperature
298 K on a Bruker Avance-III 500 MHz spectrometer equipped
with a 5 mm BBFO probe, a 19F frequency of 470.59 MHz and
be the initial reux temperature.18 These properties also sug-
gested that the storage of 2 was difficult. Therefore, a separation
device was used to collect 2, which was made to drip into
a methanol ammonia solution for the synthesis of 3. This
apparatus allowed the reaction to proceed without any pause,
which otherwise would have been essential if the advanced
purication of 2 had to be done. This set up reduced the loss of
peruoroisobutyry chloride and improved the reaction effi-
ciency. It therefore became convenient to purify the product.
Once the 3 was prepared, the synthesis of peruoroisobutryl
amide and peruoroisobutyronitrile was easy. Their synthesis
could be proceeded using the routine procedures for amination
and dehydration. The dehydration process of 4 in particular is
very well established, and hence we have not included too many
details here.
a
13C frequency of 125.76 MHz. All 19F spectra were recorded
with a recycle delay of 2 s, sweep width of 242 ppm, 220k
acquisition data points, 4 scans. All 13C spectra were recorded
with a recycle delay of 3 s, sweep width of 242 ppm, 32k
acquisition data points, 256 scans. All NMR spectra were pro-
cessed with 1 Hz line broadening.
GC-MS were carried out on Varian 450-GC Gas Chromato-
graph and Varian 320-MS TQ Mass Spectrometer. The Gas
Chromatograph was equipped with a 30 m and 0.250 mm,
0.25 mm df, VF-5 column.
Synthesis of peruoroisopropyzinc iodide
Compared to this study, the Scheme 3 as the mainstream
synthetic route of methyl peruoroisobutyrate had many
disadvantages and dangers. First, the raw material was chlor-
oformate which was a highly toxic liquid that had been
forbidden in many places. Second, the reaction in the gas–
liquid phase in the next step wasn't easy to be controlled and
operated. In fact, there was another way to synthesize C4. The
electrolytic uorination was also an effective route to prepare
methyl peruoroisobutyrate. But the route was more dangerous
and had too many by-products to be separated. Our raw mate-
rials were easier to be purchased, stored and prepared.
Furthermore, it had low chemical toxicity and good stability.
Obviously, the methodology in Scheme 2 was simpler and safer
19.5 g (0.3 mol, diameter 1–3 mm) zinc powder and 40 mL DMF
was added to a round bottom ask containing a tube for
introducing gas, a thermometer, a spherical condensing tube
and a drop funnel. Nitrogen was introduced into the apparatus
to prevent the system from air. 30 mL DMF solution containing
29.6 g (0.1 mol) peruoroisopropyl iodide was added to the
aforesaid mixture. Then the solution was heated at 60 ꢀC for 2 h
which included the feeding dropping time of about 1 h. To lter
the metal powder, the peruoroisopropylzinc iodide was ob-
tained in DMF.
Synthesis of peruoroisobutyryl acid (1) by ultrasonic method
to be used in the laboratory and its efficiency and yield were also To a round bottom ask containing a tube for introducing
no lower than any other methods.
carbon dioxide gas, a thermometer, a spherical condensing
tube and a drop funnel, was added metal powder and 40 mL
DMF. The gas-introducing tube was inserted into the solution to
ensure a better contact between carbon dioxide and the solu-
tion. The ultrasound was kept on until the reaction was over.
Experimental
General remarks
Peruoroalkyl halides were purchased from SHANG FLUORO. The speed of introducing carbon dioxide was about 0.1 L minꢁ1
.
Zinc powder was purchased from Macklin Company and its To the ask, 30 mL DMF solution containing 0.1 mol raw
diameter ranged from 1–3 m, purity was over 99.99%. Nearly material was added into 19.5 g (0.3 mol, diameter 1–3 mm) zinc
99.999% pure nitrogen gas and carbon dioxide gas were powder and 40 mL DMF. Then the solution was heated 60 ꢀC for
purchased from the WuHanShi XiangYun Industry Co. Ltd. All 2 h which included a dropping time of about 1 h. The solution
the solvents were of analytical grade and used without further was ltered to remove the remaining metal powder. Aer the
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reaction, 100 mL of 6 N hydrochloric acid was added for the 87.54, 87.24. 19F NMR (376 MHz, CDCl3): d ¼ ꢁ74.54, ꢁ74.55,
hydrolysis, and pH was adjusted to be less than 2. The solution ꢁ180.05, ꢁ180.06, ꢁ180.08, ꢁ180.09, ꢁ180.11, ꢁ180.12. MS
was now separated in two phases. Aer the lower organic layer (EI) m/z: 213 [M]+, 169 [C3F7]+, 69 [CF3]+, 44 [CONH2]+.
was distilled, dried, ltered and collected, deep brown per-
uoroisobutyryl acid was obtained.
Synthesis of peruoroisobutyronitrile (C4)
10 g peruoroisobutyryl amide and 12 mL pyridine was put in
20 mL DMF. Then 13.8 mL triuoroacetic anhydride was
dropped into the solution. The temperature was controlled
Synthesis of 1 by high-pressure method
19.5 g (0.3 mol, diameter 1–3 mm) zinc powder and 70 mL DMF
was placed in a dry high-pressure closed cylinder. The cylinder
needed to be equipped with a constant pressure drop funnel,
and containing 30 mL DMF and 29.6 g (0.1 mol) per-
uoroisopropyl iodide. Introduction of carbon dioxide main-
tained a high pressure from 1 MPa to 3 MPa in the cylinder. The
later procedures and temperature were the same as the ultra-
sonic method.
ꢀ
below 0 C. The reaction time was around 3 h. The 4.5 g per-
uoroisobutyronitrile was obtained in ice trap. The yield was
49.5%.
Colorless gas; 19F NMR (376 MHz, CDCl3): d ¼ ꢁ75.37,
ꢁ75.39, ꢁ176.49, ꢁ176.51, ꢁ176.53, ꢁ176.56, ꢁ176.58. MS (EI)
m/z: 195 [M]+, 176 [C4F6CN]+, 107 [C3F3CN]+, 100 [C2F4]+, 57
[CFCN]+,69 [CF3]+, 31 [CF]+.
Deep red liquid; 13C NMR (100 MHz, CDCl3): d ¼ 159.77,
159.57, 120.35, 120.07, 117.50, 117.23, 89.77, 89.44, 87.27. 19F
NMR (376 MHz, CDCl3): d ¼ ꢁ75.47, ꢁ75.49, ꢁ181.38, ꢁ181.40,
ꢁ181.42, ꢁ181.44, ꢁ181.46. MS (EI) m/z: 214 [M]+, 197 [M ꢁ
OH]+, 150 [C3F6]+, 69 [CF3]+, 45 [COOH]+. IR (KBr): 1772.29 cmꢁ1
(C]O).
Conclusions
In summary, we have developed a novel method for the
synthesis of peruoroisobutyronitrile from peruoroisobutyryl
acid which is a safer and more convenient route than estab-
lished patent. The compound is introduced as the new
environment-friendly insulating gas as the replacement of SF6
in high voltage electrical equipment, with the aim of abiding by
Kyoto Protocol. Peruoroisobutyryl acid could be synthesized
with ultrasound and highꢀ pressure over 1 MPa at 60 ꢀC. It
reacted with (COCl)2 at 40 C to form peruoroisobutyryl chlo-
ride that then react with NH3 to get peruoroisobutyryl amide.
Raw materials and intermediates are characterized by GC-MS,
13C NMR 19F NMR spectra in the study.
Synthesis of peruoroisobutyryl chloride (2)
To take into consideration the properties of peruoroisobutyry
chloride, a water separation reux device was used. 10.8 g (0.05
mol) peruoroisobutyryl acid along with and 12.3 mL (0.15 mol,
3.0 equivalents) THF as solvent and 10% mol DMF as catalyst
was added to a round bottom ask which included a ther-
mometer, a drop funnel and downward distilling head with
a serpentine reux condenser. Notably, the cooling medium in
the condenser was better below ꢁ10 ꢀC. 5 mL (0.06 mol, 1.2
equivalents) of oxalyl chloride was dropped into the solution in
2 h at 40 ꢀC. As the reaction progressed, a massive colorless
peruoroisobutyryl chloride was obtained below reux
condenser. The yield was nearly 60%.
Conflicts of interest
There are no conicts to declare.
Colorless liquid; 13C NMR (100 MHz, CDCl3): d ¼ 160.08,
159.88, 120.34, 120.08, 117.49, 117.23, 89.40, 87.23, 86.90. 19F
NMR (376 MHz, CDCl3): d ¼ ꢁ75.94, ꢁ75.96, ꢁ75.98, ꢁ75.99,
ꢁ168.99, ꢁ168.00, ꢁ168.01, ꢁ168.02, ꢁ168.03, ꢁ168.04,
ꢁ168.05, ꢁ168.06, ꢁ168.07. MS (EI) m/z: 232 [M]+, 197 [M ꢁ
Cl]+, 169 [C3F7]+, 100 [C2F4]+, 69 [CF3]+, 63 [COCl]+.
Acknowledgements
The works were supported by National Key R&D Program of
China (2017YFB0902500) State Grid Science & Technology
Project (the key technology of environment-friendly gas-
insulated transmission line). Besides we thank Wuhan Univer-
sity Testing Center for technical assistance.
Synthesis of peruoroisobutyryl amide (3)
11.6 g (0.05 mol) peruoroisobutyryl chloride solution was
dropped into 22 mL 7.0 M (0.15 mol NH3 in solution) NH3-
$MeOH. The temperature was controlled below 20 ꢀC. The
reaction time was around 1 h. Aer the reaction, the main solid
by-product was ammonium chloride, which was henceforth
ltered. There was still a small amount of ammonium chloride
dissolved in methanol. Methanol was removed by distillation.
To add chloroform into solution at room temperature and lter
all solid by-product. Aer being kept overnight in the refriger-
ator, peruoroisobutyl amide crystals were found to precipitate
out. The yield was 90%.
Notes and references
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Colorless crystal; 13C NMR (126 MHz, CDCl3) d ¼ 159.69,
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