Investigation of CF2 carbene on the surface of activated charcoal in the synthesis of trifluoroiodomethane via vapor-phase catalytic reaction

Article abstract of DOI:10.1016/j.jfluchem.2008.10.004

This paper investigates the synthetic mechanism of trifluoroiodomethane (CF₃I) in the reaction of trifluoromethane and iodine via vapor-phase catalytic reaction. It is suggested that CF₂ carbene is the key intermediate and is formed in the pyrolysis process of CHF₃ at high temperature. However, in pyrolysis of CHF₃ under activated charcoal (AC) existing conditions, no C₂F₄ was detected. H₂ and 2-methyl-2-butene could not trap the CF₂ carbene. When treating the remained compounds on the used AC with H₂, CH₄ is formed on the process. It is proposed that CF₂ carbene combines with AC strongly and transfers into CF₃ radical on heat. In addition, it is found that the AC is not only the catalyst supporter to form CF₃I, but also a co-catalyst to promote the formation of CF₂ carbene and CF₃ radical.

Full text of DOI:10.1016/j.jfluchem.2008.10.004

Journal of Fluorine Chemistry 130 (2009) 231–235
Contents lists available at ScienceDirect
Journal of Fluorine Chemistry
journal homepage: www.elsevier.com/locate/fluor
Investigation of CF2 carbene on the surface of activated charcoal in the synthesis
of trifluoroiodomethane via vapor-phase catalytic reaction
Guang-Cheng Yang a, Shi Lei a, Ren-Ming Pan a, Heng-Dao Quan b,
*
a School of Chemical Engineering, Nanjing University of Science & Technology, NanJing 210094, China
b National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki 305-8565, Japan
A R T I C L E I N F O
A B S T R A C T
Article history:
This paper investigates the synthetic mechanism of trifluoroiodomethane (CF3I) in the reaction of
trifluoromethane and iodine via vapor-phase catalytic reaction. It is suggested that CF2 carbene is the key
intermediate and is formed in the pyrolysis process of CHF3 at high temperature. However, in pyrolysis of
CHF3 under activated charcoal (AC) existing conditions, no C2F4 was detected. H2 and 2-methyl-2-butene
could not trap the CF2 carbene. When treating the remained compounds on the used AC with H2, CH4 is
formed on the process. It is proposed that CF2 carbene combines with AC strongly and transfers into CF3
radical on heat. In addition, it is found that the AC is not only the catalyst supporter to form CF3I, but also a
co-catalyst to promote the formation of CF2 carbene and CF3 radical.
Received 18 June 2008
Received in revised form 20 October 2008
Accepted 21 October 2008
Available online 30 October 2008
Keywords:
CF3I
CF2 carbene
CF3 radical
Activated charcoal
Mechanism
ß 2008 Elsevier B.V. All rights reserved.
1. Introduction
reacting CHF3 or C2F5H with I2 in the presence of a catalyst, which
makes the CF3I industrialization possible [12–14]. Nagasaki et al.
Trifluoroiodomethane(CF3I)has aweakC–I bond, whichmakesit
chemically and photochemically active. As a result, CF3I possesses a
short atmospheric lifetime and low global warming potential (GWP)
[1]. For example, its lifetime is a few days and GWP is the same grade
as CO2 [2]. On the other hand, CF3I is efficient in fire suppression and
SiO2 dry etching, and it is miscible with mineral oil and compatible
with refrigeration system materials. CF3I has become the current
subject as promising replacements for halon and other halohy-
drocarbons in the application of fire extinguishing agent, freezing
medium and etching gas [3–6].
By now, literatures have reported some methods to prepare
CF3I. A. Banks first prepared CF3I by the reaction of CI4 with IF5 [7].
In addition, CF3I can be synthesized by thermal decarboxylation of
silver trifluoroacetates in the presence of elemental iodine [8], by
the reaction of Hg(CF3)2 and Hg(CF3)I with elemental iodine [9], by
reaction Bi(CF3)3 and ZnBr(CF3)Á2L (L = DMF, CH3CN) with iodine
monochloride [10,11].
have studied the mechanism for CF3I synthesis on the vapor-phase
catalytic reaction, and suggested that the metal salts catalyzed the
dehydrofluorination of CHF3 to produce CF2 carbene, and the
supporter of activated charcoal (AC) catalyzed the disproportiona-
tion of CF2 carbene [15] (Scheme 1).
In our investigation, we successfully obtained CH2F2 in the
pyrolysis reaction of CHF3 under hydrogen existing conditions,
which may support the synthetic mechanism of CF3I that the CF2
carbene is the intermediate during the pyrolysis process of CHF3,
and the formed CF2 carbene transfers into CF3 radical in the
presence of AC or catalyst, furthermore CF3 radical reacts with
iodine to form CF3I in the presence of catalyst. Also it was found
that CF3I is formed in the reaction of CHF3 and I2 only in the
presence of activated charcoal without other catalyst components,
which can be attributed to that AC is not only the catalyst of
disproportionation of CF2 carbene and a porous catalyst supporter,
but also a co-catalyst to promote the formation of CF2 carbene.
Above-mentioned methods do not seem likely candidates for
large-scale production of CF3I due to the low yield and batch
processes. Currently a continuous vapor-phase catalytic process
for the manufacture of CF3I has successfully been developed by
2. Experimental
2.1. Materials
2-Methyl-2-butene (99.5%), was purchased from Shanghai Sun
Chemical Technology Co., Ltd., China. Trifluoroiodomethane were
purchased from Zhejiang Xingteng Chemical Co. Inc., China.
* Corresponding author. Tel.: +81 298 61 4771; fax: +81 298 61 4771.
E-mail address: Hengdao-quan@aist.go.jp (H.-D. Quan).
0022-1139/$ – see front matter ß 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.jfluchem.2008.10.004

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G.-C. Yang et al. / Journal of Fluorine Chemistry 130 (2009) 231–235
Table 1
Pyrolysis of trifluoromethane in the presence of ACa.
Entry
Regent
CHF3, H2
Product
CH4
1
2
CHF3, 2-methyl-2-butene
2-Methylbutane, pentadiene,
2-methyl-2-butene and its isomer
CF4, C2F6, C3F8, C2HF5
CH4, CH3CH3, CH3I
CH4
Scheme 1. .
3
4
5b
6c
CHF3
CHF3, H2, I2
CHF3, then H2 after N2 wash
CHF3, then HF after N2 wash
Activated charcoal (AC) was obtained from Shanxi Taiyuan
Activited Carbon Factory and KF (99%) was purchased from
Sinopharm Chemcial Reagent Co., Ltd., China. HF was obtained
from Blue Express, Inc. of China. I2 was purchased from Nanjing
Yicheng Chemical Co., Ltd., China.
CHF3
a
Reaction temperature is 550 8C.
First CHF3 passed through the AC in reactor for 2 h at 550 8C, then washes the AC
b
by nitrogen at 550 8C for 1 h, then hydrogen is introduced into the reactor at 550 8C
to check the products.
c
First CHF3 passed through the AC in reactor for 2 h at 550 8C, then washes the AC
by nitrogen at 550 8C for 1 h, then HF is introduced into the reactor at 550 8C to
check the products.
2.2. Instrument and apparatus
Products were analyzed by means of GC-1002 produced by
Beijing analytical instrument factory. The capillary column was a
CP-PoraPLOT Q with 0.32 mm i.d. and 30 m from J&W Scientific Inc.
The column was programmed as follows: the initial temperature
was set at 60 8C for 6 min; then the temperature was increased at
the rate of 40 8C/min, and finally reached to 200 8C and held for
11 min. The instrumental parameters were set up as follows:
injection port temperature, 200 8C; FID detector, 250 8C; the carrier
gas was N2 (0.1 MPa).
2.3.3. Pyrolysis of CHF3 in the presence of catalyst and H2
The reaction procedure and conditions were same with Section
2.3.2, but CHF3 flow was replaced by the mixture of CHF3 with
50 ml/min and H2 with 50 ml/min. Then the gas was analyzed by
GC–MS. Its data of MS are listed as follows.
1. CH4, m/z: 16, +M; 15, +CH3, 14, +CH2, 13, +CH.
GC–MS (EI, 70 eV) spectra were measured using the Shimazu
GCMS-QP2010 system equipped with GC-2010. The column was
CP-PoraPLOT Q with 0.32 mm i.d. and 30 m length from J&W
Scientific Inc. The column was programmed as above-mentioned
GC conditions. Injection port temperature, 200 8C; the carrier gas
rate, 4.1 cm3 He/min.
The BET surface area of AC were measured by mean of low
temperature adsorption of nitrogen using a micromeritics ASAP
2000. Samples were degassed under vacuum (P < 10À5 Torr) at
573K for 3 h before measurement.
2.3.4. Pyrolysis of CHF3 in the presence of AC
18 ml AC was packed into the reactor. The reaction procedure
and conditions were same as Section 2.3.2. Then the exit gas was
analyzed by GC–MS. The data of MS were same as Section 2.3.2 (see
Table 1).
2.3.5. Reaction of H2 and the remained compounds on the surface of
used AC
At 550 8C, nitrogen flow with 100 ml/min was passed through
the reactor used in Section 2.3.4 to wash the remained CHF3 for 2 h,
then H2 with 50 ml/min was introduced into the reactor for 1 h.
The outgas was passed through water, and a KOH solution to
neutralize HF generated. Finally the gas was analyzed by GC–MS.
The results were listed as follows.
2.3. Preparation of catalysts and reaction procedure
2.3.1. Preparation of catalyst
20 g AC was added into a KF solution which was prepared by
dissolving 5 g KF into100 ml de-ionized water, and keep that at
room temperature for 1 h. Then the catalyst was dried at around
100 8C for 3 h under atmospheric conditions and at around 250 8C
for 2 h under nitrogen flow conditions. Inconel reactor with 12 mm
in diameter and 300 mm in length was equipped with an inside
Inconel tube for inserting type-K thermocouples with 1 mm
diameter. All gas inlets were controlled by the mass flow meters.
1. CH4, m/z: 16, +M; 15, +CH3, 14, +CH2, 13, +CH.
2.3.6. Pyrolysis of CHF3 in the presence of AC and H2 flow
The reaction procedure and conditions were same as Section
2.3.4, but CHF3 was replaced by a mixture of CHF3 with 50 ml/min
and H2 with 50 ml/min. The outgas was analyzed by GC–MS to
obtain following results.
CH4, m/z: 16, +M; 15, +CH3, 14, +CH2, 13, +CH.
Then reaction temperature was increased to 850 8C and kept at
that temperature for 2 h, the out products were analyzed by GC–
MS. The results were same as that at 550 8C (see Table 2).
2.3.2. Pyrolysis of CHF3 in the presence of catalyst
Heated the catalyst bed to 550 8C under nitrogen flow with the
rate of 100 ml/min. Then nitrogen flow was stopped and CHF3 with
80 ml/min was introduced to reactor, 2.5 h later, the outgases
passed through water and a KOH solution to neutralize HF formed.
Then the exiting gas was analyzed by GC–MS. The data of MS are
listed as follows.
Table 2
1. CF4, m/z: 69, +CF3; 50, +CF2;
Pyrolysis of trifluoromethane on catalyst of KF/AC.
2. CF3CF3, m/z: 119, +CF3CF2, 69, +CF3, 50, +CF2;
3. CHF3, m/z: 69, +CF3, 51, +CHF2, 31, +CF;
4. CF3CF2CF3, m/z: 169, +CF3CF2CF2, 119, +CF3CF2, 100, +CF2CF2, 69,
+CF3; 50, +CF2;
5. CF3CHF2, m/z: 119, CF3CF2, 101, CF2CHF2, 69, +CF3, 51, +CHF2;
6. CF3CF2CF2CF3, m/z: 219, +CF3CF2CF2CF2, 169, +CF3CF2CF2, 150,
+CF2CF2CF2, 131, +CF2CF2CF, 119, +CF3CF2, 100, +CF2CF2, 69, +CF3;
50, +CF2.
Entry
Regent
Catalyst
Temperature
Products
(8C)
7
8
CHF3
KF/AC
KF/AC
AC
550
550
550
850
850
CF4, C2F6, CHF3, C3H8, C2F5H
CHF3, H2
H2
CH4
+
+
9
–
10
11
CHF3, H2
CHF3, H2
Empty
AC
CH4, CH2F2, CF3CH2F, CHF2CHF2
CH4
–: no products detected.

G.-C. Yang et al. / Journal of Fluorine Chemistry 130 (2009) 231–235
233
2.3.7. Reaction of HF and the remained compounds on the surface of
AC
and the mechanism of this process involves the dehydrofluorina-
tion of CHF3 to form difluorocarbene, which then dimerizes to form
TFE [16–18].
At 550 8C, nitrogen flow with 100 ml/min was passed through
the reactor used in Section 2.3.4 to wash the remained CHF3 for 2 h.
Then HF with 50 ml/min was introduced into above reactor for 1 h.
The outgas was analyzed by GC–MS to obtain following results.
CHF3, m/z: 69, +CF3, 51, +CHF2, 31, +CF.
Raphaele et al. obtained CH2F2 by reacting H2 with CHF3 at the
temperature of 775 8C, and proposed the mechanism involved CF2
carbene intermediate [16]. Wheaton and Burton used 2-methyl-2-
butene, a electron-rich alkenes, to trap CF2 carbene intermediate at
the temperature of 120 8C and obtained gem-difluoro-2,2,3-tri-
methylcyclopropane to confirm the CF2 carbene intermediate [19].
In our laboratory, CH2F2 are obtained successfully when
hydrogen is introduced into the pyrolysis process of CHF3 at
850 8C which indicates that CF2 carbene is as the reaction
intermediate in the pyrolysis process of CHF3. The results are
consistent with the CF2 carbene process depicted [16].
However, in our experimental, when AC or catalyst is charged
into reactor, TFE is not detected in the pyrolysis process of CHF3. Also
CH2F2 cannotbeobtained inthepyrolysisprocess eventhoughinthe
presence of hydrogen. Above-mentioned results indicate that the
induction period ofsyntheticmechanismof CF3I is differentfromthe
pyrolysis mechanism of CHF3. The result is attributed to the
existence of activated charcoal or catalysts in process.
As reported, in the synthetic process of CF3I by vapor-phase
catalytic reaction, induction period was suspected that the
dehydrofluorination of CHF3 to form CF2 carbene, and the CF2
carbene cover the surface on the catalyst, but no TFE reported in
by-products, [15].
To confirm above-mentioned hypothesis, we try to capture the
CF2 carbene intermediate with the help of hydrogen and an
electron-rich alkenes to confirm the CF2 carbene mechanism
during the pyrolysis process of CHF3 in the presence of AC.
Hydrogen and 2-methyl-2-butene are used as trapping reagents in
the induction period. The results are shown in Table 1. Based on the
experimental 1, we do not get CH2F2 in the products when
hydrogen is used to capture CF2 carbene, but a certain amount of
CH4 exists in products. The results indicate no free CF2 carbene
formed in the process, or the formed CF2 carbene transferred into
CH2 carbene in the presence of hydrogen to get CH4.
2.3.8. Pyrolysis of CHF3 in the presence of AC and 2-methyl-2-butene
vapor flow
The reaction procedure and conditions were same as that in
Section 2.3.4. In the process of reaction, 2-methyl-2-butene with
0.2 g/min was vaporized and introduced into the reactor at the
temperature of 100 8C. The oily products were washed by water
and analyzed by GC–MS, but gem-difluorotrimethylcyclopropane
was not detected.
2.3.9. Reaction of H2 and CHF3 in empty reactor
The reaction procedure and conditions were same as that in
Section 2.3.2. The mixture of CHF3 with 50 ml/min and H2 with
50 ml/min were introduced into an empty reactor with 850 8C, the
outgas was analyzed by GC–MS. The results were listed as follows.
1. CH4, m/z: 16, +M; 15, +CH3, 14, +CH2, 13, +CH;
2. CHF3, m/z: 69, +CF3, 51, +CHF2, 31, +CF;
3. CH2F2, m/z: 52, +M, 51, +CHF2, 33, +CH2F;
4. CF3CH2F, m/z: 102, +M, 83, +CF3CH2, 69, +CF3, 51, +CHF2, 33
+CH2F;
5. CHF2CHF2, m/z: 102, +M, 101+CHF2CF2, 83, +CHF2CHF, 63 +CHF2C,
51, +CHF2.
2.3.10. Synthesis of CF3I in the presence of AC and H2
The reactor was packed with AC, and heated to 550 8C under
nitrogen. After 2.5 h, then CHF3 with 50 ml/min, vaporized I2 with
10 g/h and H2 with 50 ml/min were passed through the reactor.
The products were neutralized by KOH solution, dried and
analyzed by GC–MS. The results were listed as follows.
Intheexperimental2inTable1, when2-methyl-2-buteneisused
as a trapping reagent in pyrolysis of CHF3, also no gem-difluoro-
trimethylcyclopropane is detected in the process. At least, formed
CF2 carbene is not so easy to combine with 2-methyl-2-butene.
The interesting results are from the pyrolysis of CH3F in the
presence of AC. If the reaction gas is only CHF3 without hydrogen,
the products contain CF4, C2F6, C3F8, and C2HF5 (see experimental 3
in Table 1). The results clearly indicate that CF3 radical exists in the
pyrolysis process.
Based on above results, we suppose that the pyrolysis
mechanism of CH3F in the presence of AC is as Scheme 2. Firstly
pyrolysis of CHF3 at high temperature leads to the dehydrofluor-
ination of unimolecular HF of CH3F to form CF2 carbene. CF2
carbene combines with AC strongly so that it do not dimerize. It
might be decomposed into carbon and F radical on the surface of
AC. F radical reacted with CF2 carbene to form CF3 radical. As the
finally results, CF3 radical becomes into CF4, C2F6, C3F8. In addition,
a part of CF2 carbene reacts with CHF3 to form by-product C2HF5. If
H2 is introduced into the reaction process, the F radical will react
with H2 to form HF so that CF4, C2F6, C3F8 and C2HF5 could not be
obtained in the process.
1. CH4, m/z: 16, +M; 15, +CH3, 14, +CH2, 13, +CH.
2. CH3CH3, m/z: 30, +M, 28, +CH2CH2, 15, +CH3;
3. CHF3, m/z: 69, +CF3, 51, +CHF2, 31, +CF;
4. CH3I, m/z: 142, +M, 127, +I.
2.3.11. Synthesis of CF3I in the presence of catalyst KF/AC and O2
The reactor was packed with AC, and heated to 550 8C under
nitrogen. After 2.5 h, then CHF3 with 50 ml/min, vaporized I2 with
10 g/h and O2 with 50 ml/min were passed through the reactor.
The products were neutralized by KOH solution, dried and
analyzed by GC–MS. The results were listed as follows.
1. CF4, m/z: 69, +CF3; 50, +CF2;
2. CF3CF3, m/z: 119, +CF3CF2, 69, +CF3, 50, +CF2;
3. CHF3, m/z: 69, +CF3, 51, +CHF2, 31, +CF;
4. CF3CF2CF3, m/z: 169, +CF3CF2CF2, 119, +CF3CF2, 100, +CF2CF2, 69,
+CF3; 50, +CF2;
+
+
+
5. CF3CHF2, m/z: 119, CF3CF2, 101, CF2CHF2, 69, CF3, 51, +CHF2;
6. CF3I, m/z: 196, +M, 127, +I, 69,
7. CF3CF2I, 246 +M, 127, +I, 119, +C2F5, 100, +C2F4, 69, +CF3; 50, +CF2;
In addition, when pyrolysis outlet gas passes through de-
ionized water, the water became into acidic from experimental 1 to
5 in Table 1, which might be attributed to that the HF formed
solved into H2O in pyrolysis process. This is another identification
to support CF2 carbene formation in the pyrolysis process of CHF3.
As reported in literature, the activation energy of elimination of a
HF molecule from CHF3 is much lower than the dissociation
3. Results and discussion
3.1. Pyrolysis of trifluoromethane on activated charcoal
It was reported that pyrolysis of CHF3 at high temperature leads
to the formation of tetrafluoroethene (TFE) as the major product,

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G.-C. Yang et al. / Journal of Fluorine Chemistry 130 (2009) 231–235
Table 3
Synthesis of CF3I in the presence of catalyst KF/ACa.
Entry
12
Regent
GC area%
CF4
3.9
CHF3
40.2
C2F6
0.4
C3F8
0.2
C2F5H
1.0
CF3I
50.3
C2F5I
4.0
CHF3, O2, I2
Reaction temperature: 550 8C.
a
Catalyst: KF/AC.
same as those of reactions in the presence of AC (see experimental
7 and 8 in Table 2). It is was presumed that AC co-catalyzes the
dehydrofluorination of CHF3 to form CF2 carbene, then CF2 carbene
combines with AC or catalyst strongly, thus CF2 carbene does not
dimerize into TFE or does not react with H2 to form CH2F2 even at
high temperature of 850 8C.
CH4 can be formed through pyrolysis of CHF3 and H2 in the
presence of KF/AC (see No. 8 in Table 2), but does not generate from
the reaction of AC and H2 (see No. 9 in Table 2). Also CH2F2 existed
in the products indicates that hydrogen capture CF2 carbene in the
pyrolysis process of CHF3 (see No. 10 in Table 2), which further
proves that CF2 carbene appears in the pyrolysis process of CHF3.
AC is the co catalyst to promote the formation of CF2 carbene and
CF3 radical in the synthesis of CF3I by vapor-phase catalytic
reaction.
Scheme 2. Proposed mechanism for the formation of CF4, C2F6, C3F8 and C2HF5.
energies of C–F bond and C–H bond, and HF elimination to form CF2
carbene may be an important pathway for CHF3 decomposition
and the CF3 radical formation [20]. In the study on the mechanism
of hydrogenation of CCl2F2 into CH2F2, van de Sandt reported that
CF2 carbene would absorb on the PdC catalyst and it was the most
important intermediate to form CH2F2, CH3F, CH4 [21].
In our experimental, we suppose that CHF3 cracks into HF and
CF2 carbene, then the CF2 carbene combines with AC tightly since
CF2 carbene itself do not form CF2=CF2, and also the trapping
reagents do not capture the CF2 carbene. Although CF2 carbene
combined with catalyst strongly do not dimerize or react with the
trapping reagents, but it will decomposed into carbon and F radical
on heat. F radical reacts with CF2 carbene to form CF3 radical, then
form CF4, C2F6, C3F8 gradually in the reaction (see Scheme 2).
When H2 joins the reaction, firstly the F radical reacts with H2 to
generate HF so that no CF3 radical forms, then CF4, C2F6, C3F8 and
C2HF5 could not be detected in the products. Based on the
experimental 4 in Table 1, the absence of CF3I in the products
during the reaction of I2 and CHF3 in the presence of H2 further
enhances our hypothesis, the primary products are CH4, CH3I. In
addition, the absence of CH2F2 is attributed to that hydrogenation
of CF2 carbene transfers into CH2 carbene, then becomes into CH4
as shown in experimental 5.
In the experimental 5 of Table 1, first CHF3 with 100 ml/min
passes through the catalyst for 2 h at 550 8C, then nitrogen with
100 ml/min washes AC surface at 550 8C for 1 h, hydrogen passes
through the catalyst to obtain CH4, which indicates that the CF2
carbene still remind on AC even though heating at 550 8C under
nitrogen flow. The results indicate that the combination between
CF2 carbene and AC is quite strong, this is correspond to that CF2
carbene itself does not easily dimerize to TFE when AC exists in the
reaction. When hydrogen is introduced into AC surface, CF2
carbene quickly transferred into CH2 carbene. The mechanism can
be schemed as following (Scheme 3).
Also we check the surface area of AC fresh (1161.7 m2/g) and
used AC (1085.0 m2/g) in the pyrolysis of CHF3, the result shows
that the surface area decreases slightly after the reaction. Might be
it can be attributed to that the coke-formation formed in the
pyrolysis process of CHF3.
3.3. Synthesis of trifluoroiodine by vapor-phase catalytic reaction
Based on the hypothesis above on the synthetic mechanism of
CF3I, the pyrolysis of CH3F in the presence of AC or catalyst KF/AC
leads to the dehydrofluorination of CH3F to form CF2 carbene, then
CF2 carbene decomposes into carbon and F radical on the surface of
AC. F radical reacts with CF2 carbene to form CF3 radical. When
iodine gas passes through catalyst bed with pyrolysis products,
CF3I is successfully prepared by vapor-phase catalytic reaction, the
results is shown in Table 3.
4. Conclusion
A series of experimental indicate that the synthetic mechanism
of CF3I is described as follows. In high temperature, AC promotes
the dehydrofluorination of CHF3 to form CF2 carbene, then CF2
carbene combines with AC strongly to form CF3 radical when F
radical generated from decomposition of CF2 carbene. Therefore,
CF2 carbene does not dimerize to form tetrafluoroethane, but takes
place disproportionation reaction to generate CF3 radical and
carbon. As the final result, CF3I is prepared from the reaction of CF3
radical reacts and iodine in the presence of AC or catalyst. In the
process, AC is not only the catalyst supporter, but also a co-catalyst
to promote CF2 carbene formation and CF3 radical to produce CF3I.
Instead of the hydrogen passing through by HF on the surface of
AC, CHF3 is detected in the product, which is attributed to that CF2
carbene in AC reacts with HF. It further confirms our hypothesis
that CF2 carbene is strongly combine with AC in the pyrolysis
process of CHF3 (see experimental 6 in Table 1).
3.2. Pyrolysis of trifluoromethane on catalyst KF/AC
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