Selective dehydrofluorination of 2-chloro-1,1,1,2-tetrafluoropropane (HCFC-244bb) to 2-chloro-3,3,3-trifluoropropene (HFO-1233xf) using nanoscopic aluminium fluoride catalysts at mild conditions

Article abstract of DOI:10.1016/j.jfluchem.2019.04.001

Aluminium chlorofluoride (ACF, AlCl_xF_3-x, x = 0.05-0.3) and high-surface aluminium fluoride (HS-AlF₃) were tested as heterogeneous catalysts for the reactivity towards 2-chloro-1,1,1,2-tetrafluoropropane (HCFC-244bb), which is a potent greenhouse gas. Selective activation and dehydrofluorination of the C–F bond was observed, under remarkable conditions, such as mild temperatures (70 °C) and without the need for a hydrogen source as a driving force. Consecutive reactions were developed by using C₆D₆ as a solvent or adding Et₃SiH. Thus, the production of the dehydrofluorination product 2-chloro-3,3,3-trifluoropropene (HFO-1233xf) can be coupled to a hydroarylation or hydrodefluorination reaction in one-pot procedures.

Full text of DOI:10.1016/j.jfluchem.2019.04.001

Accepted Manuscript
Title: Selective dehydrofluorination of
2
2
-chloro-1,1,1,2-tetrafluoropropane (HCFC-244bb) to
-chloro-3,3,3-trifluoropropene (HFO-1233xf) using
nanoscopic aluminium fluoride catalysts at mild conditions
Authors: Ma e¨ va-Charlotte Kervarec, Clara Patricia Marshall,
Thomas Braun, Erhard Kemnitz
PII:
S0022-1139(19)30054-5
DOI:
Reference:
https://doi.org/10.1016/j.jfluchem.2019.04.001
FLUOR 9304
To appear in:
FLUOR
Received date:
Revised date:
Accepted date:
13 February 2019
2 April 2019
2 April 2019
Please cite this article as: Kervarec M-Charlotte, Marshall CP, Braun T, Kemnitz
E, Selective dehydrofluorination of 2-chloro-1,1,1,2-tetrafluoropropane (HCFC-
2
44bb) to 2-chloro-3,3,3-trifluoropropene (HFO-1233xf) using nanoscopic aluminium
fluoride catalysts at mild conditions, Journal of Fluorine Chemistry (2019),
https://doi.org/10.1016/j.jfluchem.2019.04.001
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Selective dehydrofluorination of 2-chloro-1,1,1,2-tetrafluoropropane (HCFC-
44bb) to 2-chloro-3,3,3-trifluoropropene (HFO-1233xf) using nanoscopic
2
aluminium fluoride catalysts at mild conditions
Maëva-Charlotte Kervarec , Clara Patricia Marshalla,b,+, Thomas Braun *, and Erhard Kemnitz *
a,+
a,
a,
aDepartment of Chemistry, Humboldt-Universität zu Berlin, Brook-Taylor-Straße 2, D-12489 Berlin, Germany
bSchool of Analytical Sciences Adlershof (SALSA), Humboldt-Universität zu Berlin, Unter den Linden 6, D-10099 Berlin,
Germany
+
These authors contributed equally to this work
Dedicated to Prof. Norio Shibata in recognition of the ACS Award on Creative Work in Fluorine
Chemistry 2019
Graphical abstract
Highlights

A selective activation of C─F bond was achieved to transform HCFC-244bb to HFO-1233xf at
mild conditions via dehydrofluorination


Consecutive reactions were developed by adding C
6
D
6
or Et
3
SiH
Both microporous ACF and mesoporous HS-AlF are highly active catalysts
3
Abstract

Aluminium chlorofluoride (ACF, AlCl
x
F
3-x, x=0.05-0.3) and high-surface aluminium fluoride (HS-AlF )
3
were tested as heterogeneous catalysts for the reactivity towards 2-chloro-1,1,1,2-
tetrafluoropropane (HCFC-244bb), which is a potent greenhouse gas. Selective activation and
dehydrofluorination of the C─F bond was observed, under remarkable conditions, such as mild
temperatures (70°C) and without the need for a hydrogen source as a driving force. Consecutive
reactions were developed by using C
6
D
6
as a solvent or adding Et SiH. Thus, the production of the
3
dehydrofluorination product 2-chloro-3,3,3-trifluoropropene (HFO-1233xf) can be coupled to a
hydroarylation or hydrodefluorination reaction in one-pot procedures.
Keywords
aluminium fluoride · dehydrofluorination · hydrochlorofluorocarbons · C-F activation
1. Introduction
Defluorination of polyfluorinated molecules is of high interest in organofluorine chemistry, since the
demand to access new fluorinated building blocks and to develop new reaction pathways is
increasing.[1–6] Applications can be found in a variety of fields such as pharmaceuticals, materials
science, and in environmental chemistry.[7][8] One approach for the synthesis of highly fluorinated
molecules involves C─F bond activation reactions, but the development of selective reaction
pathways can be challenging, in part because the C─F bond is the strongest bond to carbon.[9–14]
However, a variety of reactions which are characterized by kinetically controlled reaction pathways
are often conceivable.[11,15]
Hydrochlorofluorocarbons (HCFCs), hydrofluorocarbons (HFCs), chlorofluorocarbons (CFCs) and
perfluorocarbons (PFCs) are known to be potent greenhouse gases exhibiting a high global warming
potential (GWP), but they can be derivatized via dehydrohalogenation to access valuable olefins.[16–
1
8] Hydrofluorolefins (HFOs) are known to have a lower GWP and are regarded as good
replacements for the HCFCs. In particular, HFO-1234yf (2,3,3,3-tetrafluoropropene) and HFO-1234ze
1,3,3,3-tetrafluoropropene) are of high interest because of their use as refrigerants used in air
(
conditioning.[19–21] It is still a challenge to activate HCFCs under mild conditions. To the best of our
knowledge, there are no reports which use less than 300°C for effective conversions. One important
intermediate among several other isomeric compounds for the synthesis of HFO-1234yf is HFO-
1
233xf (2-chloro-3,3,3-trifluoropropene, 2). There are several patents that describe the synthesis of
HFO-1233xf, using different tetrahalopropenes as starting compounds together with stabilizers,
fluorinating agents and catalysts.[18,22–24] The procedures usually comprise vapor phase
fluorination reactions at high temperature.
Recently, Mao et al investigated the transformation of 2-chloro-1,1,1,2-tetrafluoropropane (HCFC-
2
1
44bb, 1) into 2,3,3,3-tetrafluoropropene (HFO-1234yf) and 2-chloro-3,3,3-trifluoropropene (HFO-
233xf, 2) using a modified MgO catalyst.[25] In a continuous flow of HF and at elevated
temperatures, a high conversion to yield the dehydrochlorination product was obtained. In 2015,
reactions pathways for the formation of HFO-1234yf using a fluorinated chromium catalyst, SrClF,
BaClF, or HS-AlF
conditions (i.e. elevated temperature). More recently, we studied the reactivity of the highly Lewis
acidic and nanoscopic catalyst aluminium chlorofluoride (AlCl F3-x, x=0.05-0.3) towards HFO-1234yf with
3
were reported.[26] Dehydrofluorination products were detected under harsh
x
the aim to develop derivatization reactions to access new building blocks.[27] At mild conditions, and
using hydrogen sources such as silane or germane, HFO-1234yf can be converted into different
fluorinated alkene or alkane derivatives. The choice of the Lewis acid catalyst used for the
dehalogenation is very important, as demonstrated by Mao et al and by Teinz et al.[25,28] It has

been proposed that when the substrate is treated with hard Lewis acids, such as AlF
3
, it will suffer
dehydrofluorination, whereas softer Lewis acids, such as BaF , will dehydrochlorinate the substrate.
2
As one of the strongest Lewis acid catalysts, aluminum fluoride-based compounds are known to be
active towards C−F bond activation.[10] ACF (AlCl with
x
F3-x, x=0.05-0.3) is an amorphous Lewis acidic AlF
3
a chlorine content between 0.05-0.3 and it is microporous. It was discovered and patented by
DuPont in 1992 and further studies concerning its composition and properties appeared years
later.[29–32] HS-AlF is another very strong solid Lewis acid and was introduced in 2003 by Kemnitz
3
and coworkers.[33] The amorphous material is synthesized in a two-step method, combining a sol-gel
reaction and a postfluorination treatment under a flow of chlorodifluoromethane. It exhibits a high
surface area and is mesoporous. Recently, a systematic comparative study on both catalysts, using
several characterization methods to assess their acidity, was published.[34] Both ACF and HS-AlF
very strong Lewis acids and the differences between them mostly due to the different porosities, can
likewise affect their reactivity. N physisorption studies showed that their porosities differentiates
them into a mesoporous (HS-AlF ) or microporous catalyst (ACF). According to NH -TPD, they possess
a similar amount of acidic sites (see Table S1), suggesting comparable behavior in their reactivity.
3
are
2
3
3
ACF and HS-AlF are useful catalysts for several types of reactions such as dehydrofluorinations,
3
dehydrochlorinations or hydroarylations.[35–39] In the case of the first two reactions, Et SiH or
Et GeH are beneficial for effective conversions.[35,37] The silanes or germanes can affect the activity
3
3
of the catalytic system, in part because the driving force for such reactions becomes the formation of
a strong Si−F or Ge−F bond. The C─F bond is hard to activate and thus the initial step is crucial. If
silane or germane are present in the reaction mixture, a silylium/germylium-ion-like species might be
generated at the Lewis acidic catalysts surface at any step of a putative catalytic cycle, and thus
influence the conversion.[37,40] However, a major drawback for industrial application is that
expensive additives are used.
In this paper, we will present the activation of HCFC-244bb, using very mild conditions.
Dehydrofluorination reactions were coupled with consecutive reactions at the nanoscopic Lewis
acidic aluminum chlorofluoride ACF or HS-AlF as heterogeneous catalysts.
3
2. Results and Discussion
HCFC-244bb (1) was treated with ACF or HS-AlF
3
as catalysts in C D12 as a solvent (Scheme 1).
6
Formation of the fluoroolefin 2-chloro-3,3,3-trifluoropropene (HFO-1233xf) (2) by
dehydrofluorination was observed with a conversion of 61% in the presence of ACF and 78% in the
presence of HS-AlF .
3
Scheme 1. Reaction products for the dehydrofluorination of 2-chloro-1,1,1,2-tetrafluoropropane (1) in C
12 (top).
6 6
D (bottom) and
6
C D
Then C
6
D was used as a solvent in order to achieve after the dehydrofluorination step a subsequent
6
hydroarylation in a consecutive reaction (Scheme 1). Indeed, the formation of HFO-1233xf (2)
together with the hydroarylation product 3 was observed in a product ratio 2:3 of 1:1 for ACF and
1
:10 for HS-AlF (Table 1, entries 1 and 3). The formation of 3 is also consistent with previous studies
3

at ACF, where various combinations of arenes and olefins were tested, giving the hydroarylation
products with very high conversions under mild conditions.[38] This two-step reaction explains the
selectivity observed here, which differs for ACF and HS-AlF
3
.
Since the acidity of both catalysts is comparable (see above, Table S1), the porosity might play a role.
The consecutive dehydofluorinations and hydroarylations occur much faster on HS-AlF , providing as
a consequence a higher selectivity to product 3. The better accessibility of acidic sites due to the
mesoporous nature of HS-AlF , allows a better performance to produce the hydroarylation product 3.
3
3
In order to prove the activation of the double bond at 2 separately, independent reactions were
carried out, and the reactivity of HFO-1233xf (2) in C in the presence of ACF and HS-AlF was
investigated. Indeed, the conversions yielded the hydroarylation product 3 (Scheme 2, Table S5).
6
D
6
3
6 3 6 6
Scheme 2. Reactivity of 2-chloro-3,3,3,-trifluoropropene in C D12 and Et SiH (top) and in C D (bottom).
The results are remarkable, because neither in C
needed for activating the C─F bond in HCFC-244bb (1) at ACF or HS-AlF
for a dehydrofluorination at either ACF and HS-AlF without the presence of an additional hydrogen
6
D
6
6
nor in C D
12 an additional hydrogen source is
3
. This is a very rare example
3
source.[37] Moreover, the C─Cl bond remains untouched in all the conditions. This is in accordance
with studies on selective dehydrofluorination and dehydrochlorination reactions of 3-chloro-1,1,1,3-
tetrafluorobutane at AlF
3
or BaF . If only C─Cl bonds are present in a substrate, they can be as well
2
activated as shown by various reports in the literature.[35,36] It was shown, that if both C─F and C─Cl
bonds are present in a substrate, ACF may promote competitive hydrodechlorination and
dismutation reactions.
Possible mechanistic reaction pathways are in accordance with the literature.[38] After an initial C–F
bond cleavage at the Lewis acidic surface, a carbenium-like surface-species is formed. In C
recombination of the fluoride and a proton result in the release of HF and generation of HFO-1233xf
2). With C as solvent, the hydroarylation product 3 can be formed subsequently by a surface
mediated reaction of 2, as described before.[38] A Wheeland intermediate formed by attack of the
by a carbenium ion which was generated by activation of the CF group in 2 (see further below)
is less likely, because after deuterium migration this would result in the generation of the olefin
C=CCl-CH (4), which was not observed at all. However, 4 could in principle convert into 3 by
DF addition to the double bond.
6
D
12
,
(
D
6 6
6
C D
6
3
F
2
2 6 5
C D

3
Scheme 3. Reaction pathways for the generation of 2 and 3; Cat: ACF, HS-AlF .
Table 1 Reactivity of ACF and HS-AlF
Entry Solvent Catalyst
3
towards
1
in C
6
D
6
or C
6
D
12 as solvents
t [days]
Products
Conversion [%][a]
TON[b]
1
2
3
4
C
C
C
C
6
6
6
6
D
D
D
D
6
ACF
ACF
HS-AlF
HS-AlF
3
2
3
2
and
and
2
2
(1:1)
7
7
7
7
55
61
67
78
5
5
6
7
12
6
3
3
(10:1)
12
[
a]
19
as internal standard [b] Assuming 1 mmol active sites/g catalyst (NH
Calculated via F NMR using a capillary of PhCF
for both ACF and HS-AlF
3
3
-TPD)
3
Even though a hydrogen source is not needed to observe the reactivity with 1 described above, it
was of interest to add a silane in order to compare with previous studies.[35,37] Activation reactions
of HFO-1234yf, HFO-1234ze and fluorinated or chlorinated methanes at ACF can be promoted
considerably and in addition different selectivities have been observed. Therefore, experiments were
carried out in the presence of Et
Scheme 4).
3
SiH, either with additional C
6
D
6
or C
6
D
12 or in neat Et SiH (see
3
3
Scheme 4. Reaction products for dehydrofluorination of 2-chloro-1,1,1,2-tetrafluoropropane (1) in the presence of Et SiH as
a hydrogen source.

Reactions of HCFC-244bb (1) with neat Et
chloro-3,3,3-trifluoropropene (2) by dehydrofluorination for both catalysts (see Table 2, entries 3 and
). The fluorinated silane Et SiF was formed instead of HF. This observation is remarkable, because
3
SiH at 70 °C afforded selectively only the fluoroolefin 2-
6
3
with other substrates such as fluorinated methanes the presence of silanes promotes the reactivity
considerably.37 However, conversions are slightly lower than when no silane was present in the
reaction mixture. This might be explained by the fact that Et
of the acid sites, preventing the substrate to adsorb at the surface. When C
conversions went up to 84% (Table 2, entries 2 and 5), and the dehydrofluorination product 2-chloro-
,3,3,-trifluoropropene (2) was again generated as the main compound. In addition, a small amount
of 2-chloro-3,3-difluoropropene (5) was formed with both catalysts. Depending on the catalyst used,
the ratio of the products differs slightly. For HS-AlF , the products 2 and 5 were generated in a 10:1
3
SiH, which is in excess, can block some
6
D
12 was used as solvent,
3
3
ratio, whereas when ACF was used as catalyst the ratio is 4:1.
Based on comparison with the reactivity of the fluoroolefin HFO-1234yf with ACF, it is likely that
some of the in situ produced HFO-1233xf (2) suffers an allylic hydrodefluorination in the presence of
Et
fluorinated building block.[9] Note that when HFO-1234yf was treated with ACF in Et
only traces of the monohydrodefluorination product were obtained.[27] However, in accordance
with these results, when C is used as a solvent, the Friedel-Crafts product 4 and 2-chloro-3,3,3-
trifluoropropene (2) are produced in a ratio 5 to 1 (Table 2, entries 1 and 4) with HS-AlF as catalyst.
3
SiH.[27,41–43] Remarkably, only one C─F bond of the product 2 reacts to access 5 as a new
3
SiH and C
D ,
6 12
D
6 6
3
Furthermore, traces of the hydroarylation product 3 are generated. In the case of ACF, on the other
hand, the selectivity is slightly different and HFO-1233xf (2), the hydroarylation product 3, as well as
Friedel-Crafts product 4 are formed in a ratio of 1:1:4. It is known from previous reports that olefinic
substrates can undergo Friedel-Crafts type reactions, as well as hydroarylation reactions, when ACF is
used as a catalyst.[38]
To prove independently that HFO-1233xf (2) undergoes hydrodefluorination, it was treated with
Et
slowly formed in the case of HS-AlF
correlates to the different product ratio observed for both catalysts. An additional reaction was
performed for ACF, where an excess of silane together with C 12 as the solvent was used. The ratio
of 2:5 was in this case 10:1, suggesting that an excess of silane might block the acidic sites, and the
3
SiH and the catalysts in C
6
D
12 (see Scheme 2 and Table S5). Small amounts of product 5 were
3
, and for ACF a faster conversion of 2 into 5 was obtained, which
6
D
product 2 cannot further react to form the fluoroolefin 5. When no solvent is used, the Et
not play any role in the reaction and only HFO-1233xf (2) was formed.
3
SiH does
Table 2 Reactivity of ACF and HS-AlF
Entry Solvent Hydrogen source Catalyst Products (ratio)
3 3
in the presence of Et SiH
t [days] Conversion [%][a]
TON[b]
1
2
3
4
5
6
C
C
-
6
D
D
6
Et
Et
Et
Et
Et
Et
3
3
3
3
3
3
SiH
SiH
SiH
SiH
SiH
SiH
ACF
ACF
ACF
HS-AlF
HS-AlF
HS-AlF
2
2
2
2
2
2
,
3
and
4
(1:1:4)
7
7
7
7
7
7
48
78
45
51
84
47
4
7
4
4
7
4
6
12
and
5
(4:1)
C
C
-
6
D
D
6
3
3
3
and
and
4
5
(1:5)
(10:1)
6
12
[
a]
19
[b]
Calculated via F NMR using a capillary of PhCF
both ACF and HS-AlF
3
as internal standard Assuming 1 mmol active sites/g catalyst (NH -TPD) for
3
3
The described reactivity of 1 and 2 in the presence of silane is consistent to a previous report on the
activation of fluoroalkanes such as 1-fluoropentane using ACF as the catalyst, for which in the
presence of C
6
D
6
and Et SiH, dehydrofluorination products, as well as Friedel-Crafts type products
3

were observed.[37] However, no allylic monodehydrofluorination products such as 5 or 4 were
detected, the generation of which is induced by the presence of silane. Scheme 5 shows possible
pathways for the reactivity observed for both ACF and HS-AlF
together with Et SiH, a consecutive hydrodefluorination of the intermediate HFO-1233xf (2) takes
place. An abstraction of a fluoride by the surface of the catalyst from the CF group in 2 yields Et SiF
in the presence of silane and the hydrodefluorination product 5. We assume that the C─F activation
step is supported by the presence of silane.[40] In C a Friedel-Crafts-like reactivity occurs and 4 is
3
. When C
6
D12 is used as a solvent
3
3
3
D
6 6
furnished. Note also that a possible addition of DF to 4 resulting in 3 might be hampered because of
the silane present. An alternative reaction pathway for the activation of 2 could involve an activated
silane species at the surface, which induces a C–F activation step, but such a mechanism is less
probable because of the generation of 2 only in neat silane.[35,37,40]
3 3 6 6
Scheme 5. Reactivity of 2 at ACF and HS-AlF (Cat) in neat Et SiH (left) or with additional C D as solvent (right).
For comparison, the reactivity of 1 was tested using AlCl
of silane. Instead of observing dehydrofluorination products, only Cl/F exchange reactions were
obtained, giving 2,2-dichloro-1,1,1-trifluoropropane. Moreover, AlCl is not a nanoscopic amorphous
material, already differentiating itself from ACF and HS-AlF . The fluorination of AlCl is driven by the
formation of the Al–F bond, which is thermodynamically favored, due to the high enthalpy of
fluorination of AlCl .[31]
3
as a catalyst in solvent and in the presence
3
3
3
3
Finally, an interesting outcome from our studies with 2-chloro-1,1,1,2-tetrafluoropropane as a
substrate is that ACF and HS-AlF do not show major differences in their catalytic properties. The
character of the two catalysts is different, because of their porosity and acidity. In previous work it
3

was shown that they are comparable, however not similar, and thus their reactivity towards certain
molecules may be different.[3]
3. Conclusion
It has been demonstrated that ACF and HS-AlF
-chloro-1,1,1,2-tetrafluoropropane HCFC-244bb (1) The conversions occur under mild conditions in
comparison to other more widespread catalysts such as fluorinated chromia.[44,45] Remarkably, in
consecutive reactions, the produced olefin HFO-1233xf (2) can undergo in the presence of C D a
3
are very good catalysts for the dehydrofluorination of
2
6
6
hydroarylation or in the presence of silane a hydrodefluorination in one-pot reactions. The second
reaction steps have also been confirmed in independent reactions.
4
. Experimental Details
4
.1 Materials and methods
JYoung NMR tubes and conventional Schlenk techniques were used to perform the reactions. C
D
6 6
was dried over K-Solvona and distilled before usage. C 12 was dried over molecular sieves and
6
D
purged by bubbling argon. Both solvents were purchased from Eurisotop. Et SiH (99%) was
3
purchased from Sigma Aldrich and stored under argon atmosphere. 2-chloro-1,1,1,2-
tetrafluoropropane (HCFC-244bb) and 2-chloro-3,3,3-trifluoropropene (HFO-1233xf) were a gift from
Arkema. ACF and HS-AlF
3
were synthesized according to the literature and stored in a
glovebox.[30,33] The number of active sites was determined by NH
acidic sites/g catalyst.
3
-TPD, to be roughly 1 mmol
NMR spectra of liquid samples were recorded on a Bruker DPX 300 at room temperature using a
1
capillary of trifluorotoluene as an external standard for quantification purposes. H NMR chemical
19
shifts were referenced to residual C
6
D
5
H (δ=7.16 ppm) or C D11H (δ=1.38 ppm). The F NMR spectra
6
were referenced to PhCF (δ=-63.5 ppm).
3
GC-MS experiments were conducted at an Agilent 6890N gas-phase chromatograph (Agilent 19091S-
33 Hewlett-Packard) with an Agilent 5973 Network mass selective detector at 70 eV and an HP-5ms
column.
4
4
.2 Procedure for reactions with HCFC-244bb (1) and HCFO-1233xf (2)
2
5 mg of the catalyst (ACF or HS-AlF
3
) were weighed in a JYoung tap NMR tube inside a glovebox. 0.5
SiH (60 μL, 0.5 mL) were added under
mL of the solvent (C
6
D
6
, C
6
D
12) and in certain experiments Et
3
Schlenk conditions and afterwards the gas was introduced. The condensation of the gas to the tube
was performed from a small glass bulb filled with 0.5 atm (0.21 mmol) of HCFC-244bb (1) or HFO-
1
233xf (2). After an initial measurement of NMR data, the tubes were heated at 70 °C and the
1
19
reaction was monitored over time (1, 3 and 7 days) by H and F NMR spectroscopy. Conversions
were calculated based on the consumed substrate by the integration of F NMR spectra using PhCF
19
3
as external standard in a closed capillary. Blank tests were performed likewise, in which the same
procedure was applied, without adding catalyst. Analogous experiments to the ones with HCFC-
2
44bb (1) were done, in which the catalyst was replaced by anhydrous AlCl (99.99%, trace metals
3
basis, Sigma-Aldrich).
Acknowledgments

The studies were funded by the graduate school SALSA (School of Analytical Sciences Adlershof) and
the CRC 1349 (project number 387284271) both funded by the Deutsche Forschungsgemeinschaft
(DFG, German Research Foundation).
References
[
1]
T. Ahrens, J. Kohlmann, M. Ahrens, T. Braun, Functionalization of Fluorinated Molecules by
Transition-Metal-Mediated C–F Bond Activation To Access Fluorinated Building Blocks, Chem.
Rev. 115 (2015) 931–972. doi:10.1021/cr500257c.
[
[
[
[
[
[
2]
3]
4]
5]
6]
7]
M. Shimizu, T. Hiyama, Modern Synthetic Methods for Fluorine-Substituted Target Molecules,
Angew. Chemie Int. Ed. 44 (2005) 214–231. doi:10.1002/anie.200460441.
T. Braun, R. Hughes, Organometallic Fluorine Chemistry (Topics in Organometallic Chemistry,
5
2), Springer, Cham, 2015.
Peer Kirsch, Modern Fluoroorganic Chemistry. Synthesis, Reactivity, Applications, John Wiley
&
Sons, Ltd, 2013.
D. O’Hagan, Understanding organofluorine chemistry. An introduction to the C–F bond, Chem.
Soc. Rev. 37 (2008) 308–319. doi:10.1039/B711844A.
S. Purser, P.R. Moore, S. Swallow, V. Gouverneur, Fluorine in medicinal chemistry, Chem. Soc.
Rev. 37 (2008) 320–330. doi:10.1039/B610213C.
E.P. Gillis, K.J. Eastman, M.D. Hill, D.J. Donnelly, N.A. Meanwell, Applications of Fluorine in
Medicinal Chemistry, J. Med. Chem. 58 (2015) 8315–8359.
doi:10.1021/acs.jmedchem.5b00258.
[
8]
J. Wang, M. Sánchez-Roselló, J.L. Aceña, C. del Pozo, A.E. Sorochinsky, S. Fustero, V.A.
Soloshonok, H. Liu, Fluorine in Pharmaceutical Industry: Fluorine-Containing Drugs Introduced
to the Market in the Last Decade (2001–2011), Chem. Rev. 114 (2014) 2432–2506.
doi:10.1021/cr4002879.
[
[
[
[
9]
F. Jaroschik, Picking One out of Three: Selective Single C-F Activation in Trifluoromethyl
Groups, Chem. - A Eur. J. (2018). doi:10.1002/chem.201801702.
10] T. Krahl, E. Kemnitz, Aluminium fluoride – the strongest solid Lewis acid: structure and
reactivity, Catal. Sci. Technol. 7 (2017) 773–796. doi:10.1039/C6CY02369J.
11] H. Amii, K. Uneyama, C−F Bond Activation in Organic Synthesis, Chem. Rev. 109 (2009) 2119–
2
183. doi:10.1021/cr800388c.
12] Q. Shen, Y.G. Huang, C. Liu, J.C. Xiao, Q.Y. Chen, Y. Guo, Review of recent advances in C-F bond
activation of aliphatic fluorides, J. Fluor. Chem. 179 (2015) 14–22.
doi:10.1016/j.jfluchem.2015.07.007.
[
[
13] N.A. LaBerge, J.A. Love, Activation and Formation of Aromatic C–F Bonds, in: Springer, Cham,
2
015: pp. 55–111. doi:10.1007/3418_2015_90.
14] K. Fuchibe, R. Oki, H. Hatta, J. Ichikawa, Single C−F Bond Activation of the CF
3
Group with a
Lewis Acid: CF ‐Cyclopropanes as Versatile 4,4‐Difluorohomoallylating Agents, Chem. – A Eur.
J. 24 (2018) 17932–17935. doi:10.1002/chem.201805054.
3
[
[
15] T. Stahl, H.F.T. Klare, M. Oestreich, Main-Group Lewis Acids for C–F Bond Activation, ACS
Catal. 3 (2013) 1578–1587. doi:10.1021/cs4003244.
16] W.T. Sturges, W.T. Wallington, Hurley, Shine, Sihra, Engel, Oram, Penkett, Mulvaney,
Brenninkmeijer, A potent greenhouse gas identified in the atmosphere: SF(5)CF(3), Science.

2
89 (2000) 611–3. doi:10.1126/science.289.5479.611.
[
17] B.O. Bolaji, Z. Huan, Ozone depletion and global warming: Case for the use of natural
refrigerant – a review, Renew. Sustain. Energy Rev. 18 (2013) 49–54.
doi:10.1016/J.RSER.2012.10.008.
[
[
18] A. Pigamo, Process of fluorination in liquid phase, US 8,889,925 B2, 2010.
https://patents.google.com/patent/US8889925B2/en (accessed October 25, 2018).
19] P. Javidmand, K.A. Hoffmann, A comprehensive modeling of choked two-phase flow through
short-tube orifices with application to alternative refrigerants HFO-1234yf and HFO-1234ze,
Int. J. Refrig. 69 (2016) 114–135. doi:10.1016/J.IJREFRIG.2016.06.003.
[
20] G. Righetti, C. Zilio, G.A. Longo, Comparative performance analysis of the low GWP
refrigerants HFO1234yf, HFO1234ze(E) and HC600a inside a roll-bond evaporator, Int. J.
Refrig. 54 (2015) 1–9. doi:10.1016/J.IJREFRIG.2015.02.010.
[
[
21] D.C. Merkel, H.S. Tung, K.A. Pokrovski, S. Bektesevic, R.C. Johnson, H. Wang, Integrated
process to produce 2,3,3,3-tetrafluoropropene, US 8,058.486 B2, 2011. doi:10.1016/j.(73).
22] X. Sun, M.J. Nappa, Selective catalytical dehydrochlorination of hydrochlorofluorocarbons, US
8
2
.884.082 B2, 2012. https://patents.google.com/patent/US8884082B2/en (accessed October
5, 2018).
[
23] L. Wendlinger, A. Pigamo, P. Bonnet, PROCESS FOR THE MANUFACTURE OF 2-CHLORO-3,3,3-
TRIFLUOROPROPENE (HCFO 1233xf) BY LIQUID PHASE FLUORINATION OF
PENTACHLOROPROPANE, US 2014/0155659 A1, 2010.
https://patents.google.com/patent/US20140155659A1/en (accessed October 25, 2018).
[
[
24] D.C.. Merkel, H.S.. Tung, Method for producing 2-chloro-3,3,3,-trifluoropropene (HCFC-
1
233xf), US 9, 902, 671 B2, 2017. https://patents.google.com/patent/US9902671B2/en
(accessed October 25, 2018).
25] W. Mao, Y. Bai, W. Wang, B. Wang, Q. Xu, L. Shi, C. Li, J. Lu, Highly Selective
Dehydrochlorination of 1,1,1,2-Tetrafluoro-2-chloropropane to 2,3,3,3-Tetrafluoropropene
over Alkali Metal Fluoride Modified MgO Catalysts, ChemCatChem. 9 (2017) 824–832.
doi:10.1002/cctc.201601259.
[
[
[
26] K. Teinz, S.R. Manuel, B. Bin Chen, A. Pigamo, N. Doucet, E. Kemnitz, Catalytic formation of
2
,3,3,3-tetrafluoropropene from 2-chloro-3,3,3-trifluoropropene at fluorinated chromia: A
study of reaction pathways, Appl. Catal. B Environ. 165 (2015) 200–208.
doi:10.1016/J.APCATB.2014.09.076.
27] G. Meißner, K. Kretschmar, T. Braun, E. Kemnitz, Consecutive Transformations of
Tetrafluoropropenes: Hydrogermylation and Catalytic C−F Activation Steps at a Lewis Acidic
Aluminum Fluoride, Angew. Chem. Int. Ed. 56 (2017) 16338–16341.
doi:10.1002/anie.201707759.
28] K. Teinz, S. Wuttke, F. Börno, J. Eicher, E. Kemnitz, Highly selective metal fluoride catalysts for
the dehydrohalogenation of 3-chloro-1,1,1,3-tetrafluorobutane, J. Catal. 282 (2011) 175–182.
doi:10.1016/j.jcat.2011.06.013.
[
[
29] A. Sievert, C. Krespan, F. Weigert, Process for chlorofluoropropanes, US5157171A, 1992.
30] T. Krahl, R. Stösser, E. Kemnitz, G. Scholz, M. Feist, G. Silly, J.Y. Buzaré, Structural insights into
aluminum chlorofluoride (ACF), Inorg. Chem. 42 (2003) 6474–6483. doi:10.1021/ic034106h.
[
31] T. Krahl, E. Kemnitz, The very strong solid Lewis acids aluminium chlorofluoride (ACF) and
bromofluoride (ABF)-Synthesis, structure, and Lewis acidity, J. Fluor. Chem. 127 (2006) 663–

6
78. doi:10.1016/j.jfluchem.2006.02.015.
[
[
32] C.G. Krespan, V. a. Petrov, The Chemistry of Highly Fluorinated Carbocations., Chem. Rev. 96
(1996) 3269–3302. doi:10.1021/cr941144x.
33] E. Kemnitz, U. Groß, S. Rüdiger, C.S. Shekar, Amorphous metal fluorides with extraordinary
high surface areas, Angew. Chemie - Int. Ed. 42 (2003) 4251–4254.
doi:10.1002/anie.200351278.
[
[
[
[
[
34] B. Calvo, C.P. Marshall, T. Krahl, J. Kröhnert, A. Trunschke, G. Scholz, T. Braun, E. Kemnitz,
Comparative study of the strongest solid Lewis acids known: ACF and HS -AlF 3, Dalt. Trans. 47
(2018) 16461–16473. doi:10.1039/C8DT03279C.
35] A.K. Siwek, M. Ahrens, M. Feist, T. Braun, E. Kemnitz, Activation of Chlorinated Methanes at
the Surface of Nanoscopic Lewis Acidic Aluminum Fluorides, ChemCatChem. 9 (2017) 839–
8
45. doi:10.1002/cctc.201601238.
36] G. Meißner, M. Feist, T. Braun, E. Kemnitz, Selective reduction of a C−Cl bond in halomethanes
with Et 3 GeH at nanoscopic Lewis acidic Aluminium fluoride, J. Organomet. Chem. 847 (2017)
2
34–241. doi:10.1016/j.jorganchem.2017.04.030.
37] G. Meißner, D. Dirican, C. Jäger, T. Braun, E. Kemnitz, Et 3 GeH versus Et 3 SiH: controlling
reaction pathways in catalytic C–F bond activations at a nanoscopic aluminum chlorofluoride,
Catal. Sci. Technol. 7 (2017) 3348–3354. doi:10.1039/C7CY00845G.
38] B. Calvo, J. Wuttke, T. Braun, E. Kemnitz, Heterogeneous Catalytic Hydroarylation of Olefins at
a Nanoscopic Aluminum Chlorofluoride, ChemCatChem. 8 (2016) 1945–1950.
doi:10.1002/cctc.201600257.
[
[
39] V.A. Petrov, C.G. Krespan, B.E. Smart, Isomerization of halopolyfluoroalkanes by the action of
aluminum, J. Fluor. Chem. 89 (1998) 125–130.
40] M. Ahrens, G. Scholz, T. Braun, E. Kemnitz, Catalytic hydrodefluorination of fluoromethanes at
room temperature by silylium-ion-like surface species, Angew. Chemie - Int. Ed. 52 (2013)
5
328–5332. doi:10.1002/anie.201300608.
[
[
41] K. Fuchibe, H. Hatta, K. Oh, R. Oki, J. Ichikawa, Lewis Acid Promoted Single C-F Bond Activation
of the CF 3 Group: S N 1′-Type 3,3-Difluoroallylation of Arenes with 2-Trifluoromethyl-1-
alkenes, Angew. Chemie Int. Ed. 56 (2017) 5890–5893. doi:10.1002/anie.201701985.
42] T. Ahrens, M. Teltewskoi, M. Ahrens, T. Braun, R. Laubenstein, Competing reaction pathways
of 3,3,3-trifluoropropene at rhodium hydrido, silyl and germyl complexes: C–F bond activation
versus hydrogermylation, Dalt. Trans. 45 (2016) 17495–17507. doi:10.1039/C6DT03027K.
[
[
43] T. Fujita, K. Fuchibe, J. Ichikawa, Transition Metal-Mediated and -Catalyzed C-F Bond
Activation via Fluorine Elimination, Angew. Chemie. (2018). doi:10.1002/ange.201805292.
44] D.C. Merkel, H.S. Tung, Method for producing 2-chloro-3,3,3,-trifluoropropene (HCFC-1233xf),
US7,795,480B2, 2008. https://patents.google.com/patent/US7795480B2/en (accessed
October 25, 2018).
[
45] T. Nakajima, B. ꢀemva, A. Tressaud, Advanced Inorganic Fluorides Synthesis, Characterization,
and Applications, 1st ed, Elsevier, Amsterdam, 2000.