Thermal chlorofluorination of propyne and propadiene

Article abstract of DOI:10.1016/j.jfluchem.2006.09.007

Propyne and propadiene have been found to readily undergo vapor phase catalyzed chlorofluorination. At temperatures to 285 °C, the reaction forms mixtures of C₃F₄Cl₄ isomers that differ in composition from mixtures obtained from either propane or propene.

Full text of DOI:10.1016/j.jfluchem.2006.09.007

Journal of Fluorine Chemistry 127 (2006) 1611–1615
www.elsevier.com/locate/fluor
Short communication
Thermal chlorofluorination of propyne and propadiene
*
Randolph K. Belter
Department of Chemistry and Physics, Southeastern Louisiana University, Hammond, LA 70402, United States
Received 3 January 2006; received in revised form 6 September 2006; accepted 6 September 2006
Available online 10 September 2006
Abstract
Propyne and propadiene have been found to readily undergo vapor phase catalyzed chlorofluorination. At temperatures to 285 8C, the reaction
forms mixtures of C3F4Cl4 isomers that differ in composition from mixtures obtained from either propane or propene.
# 2006 Elsevier B.V. All rights reserved.
Keywords: Chlorofluorination; Propyne; 1,2-Propadiene; Tetrachlorotetrafluoropropane
1. Introduction
temperature, vapor phase chlorofluorination of propane or
propene over chromia catalyst.
For decades chlorofluorocarbons (CFCs) and bromofluor-
ocarbons have been useful chemicals for refrigeration, solvent,
plastic foam manufacture and firefighting applications. The
discovery of the harmful nature of these chemicals towards the
earth’s protective ozone layer has led to the outlawing of the
manufacture and use of most of these chemicals. Industry has
been forced to find suitable replacements and has done so in
many instances with hydrofluorocarbons (HFCs). In firefighting
applications Halon-13B1 (CF3Br) was replaced by HFC-227ea
(1,1,1,2,3,3,3-heptafluoropropane). HFC-227ea, like all the
chlorine- and bromine-free hydrofluorocarbons, has zero ozone
depleting potential.
High temperature chlorofluorination of propane and propene
is also described in the US patent application of Great Lakes
Chemical Corp. [4]. This process chlorofluorinates either 3-
carbon feedstock to produce 2,2-dichloro-hexafluoropropane,
2. Hexafluoro-substituted 2 is then subjected to more strenuous
fluorination conditions to force one more fluorine substitution
to occur, producing 2-chloro-1,1,1,2,3,3,3-heptafluoropropane,
1. A third and final step of vapor phase hydro-dehalogenation
replaces the remaining chlorine substituent with hydrogen to
produce the ultimate desired product 1,1,1,2,3,3,3-heptafluor-
opropane, 3, rather than HFP (see Scheme 2).
In the above mentioned processes, propane or propene are
chlorofluorinated with HF and chlorine to produce, at a
minimum, hexafluorinated material. In such a reaction, 14 mol
of hydrogen chloride (HCl) are generated for every mole of
propane converted to 2. Eight moles of HCl are produced in
chlorine-for-hydrogen exchange and 6 mol are produced in
fluorine-for-chlorine exchange. Propene fares better as the
addition reaction of Cl2 or HF across the double bond
eliminates the generation of 2 mol of HCl.
The firefighting agent HFC-227ea is prepared industrially by
the simple addition of HF to hexafluoropropylene (HFP).
Hexafluoropropylene is manufactured as a by-product or
intentional co-product of tetrafluoroethylene manufacture and
is useful as a monomer itself. In order to improve the
availability of HFP and/or HFC-227ea, several processes [1–4]
have been developed that are independent of TFE manufacture.
E.I. Du Pont de Nemours has patented a process for producing
hexafluoropropylene by first producing 2-chloro-1,1,1,2,3,3,3-
heptafluoropropane, 1, then hydrodehalogenating it to produce
HFP [1] (see Scheme 1). The production of the 2-chloro-
1,1,1,2,3,3,3-heptafluoropropane, 1, is brought about by high
Excessive HCl generation is problematic to the operation of
any hydrofluorocarbon manufacturing facility as it makes for
more difficult separation of products and recyclable HF and
chlorine from the HCl stream. Further, excessive HCl
production by the industry as a whole has made it more and
more difficult to dispose of HCl as a product on the open
market. Just as the use of propene decreases the amount of HCl
produced in chlorofluorination by two equivalents, it is a
* Tel.: +1 985 549 3529; fax: +1 985 549 5126.
E-mail address: rbelter@selu.edu.
0022-1139/$ – see front matter # 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.jfluchem.2006.09.007

1612
R.K. Belter / Journal of Fluorine Chemistry 127 (2006) 1611–1615
carbon molar ratio of 9–12:1 to ensure full chlorine-for-
hydrogen exchange in the first reactor zone, but in practice, the
chlorine feed could be nearly stoichiometric without any
detrimental effects. Thorough dilution of the hydrocarbon and
chlorine feeds in the HF is essential for minimizing by-product
formation. As such, the HF feed was split into two equal
streams. One stream was mixed with hydrocarbon and the other
stream was mixed with chlorine. The two streams were
vaporized each in a separate vaporizer. The two streams were
recombined at the entrance to the reactor.
Scheme 1.
Scheme 2.
stoicheometric fact that if propyne could be successfully used
as a feedstock for chlorofluorination, it would be possible to
produce 1 or 2 with four less equivalents of by-product HCl
than is produced with propane. For 2, that would be a reduction
in HCl of 29%. In terms of operation and disposal costs, such a
reduction is significant.
The Du Pont and the Great Lakes patents show that product
composition may be changed by the choice of catalyst. For the
preparation of saturated chlorofluoropropanes, catalysts based
on iron, chromium or nickel are recommended. In verification
studies on propene, chromium-based catalysts were found to be
preferred. While iron based catalysts are reported to be more
selective, excessive amounts of fragmentation of the C-3 chain
into C-1 and C-2 compounds were observed with FeCl3 on
carbon.
The initial goal of this project was to determine whether
propyne could, in fact, serve as a viable feedstock for high
temperature vapor phase chlorofluorination. Additionally, it
became a goal of this project to analyze the isomeric
composition of the chlorofluorination products of propane,
propene and propyne and to look for variations in those
compositions.
2.2. Control experiments on propane and propene
With propane and propene feed rates of 0.25 mol/h, the
24 in. reactor provided sufficient residence time for complete
chlorination, with no more than trace quantities of hydrogen-
substituted material observed. While the reactor did produce
some 2,2-dichloro-1,1,1,3,3,3-hexafluoropropane, 2, mostly
lesser-fluorinated materials were isolated. Trifluoro-, tetra-
fluoro- and pentafluoro-substituted chloropropanes were
essentially the exclusive products for either feedstock, with
tetrafluoro predominating. With yields of 90%, fluorine content
was 67% of theoretical for CF3–CCl2–CF3.
2. Results and discussion
2.1. Reaction conditions
Initially, control experiments were run on propane and
propene in order to determine acceptable operating parameters
for a reactor. Reactions were performed in a single 1 in.
(2.5 cm) diameter tubular reactor, 24 in. (61 cm) long, with two
electrically heated temperature zones of equal length. As
described in the literature [4], it is advisable to perform
chlorofluorination reactions of hydrocarbons in two stages. A
first stage reaction is performed at a lower temperature of
between 225 and 285 8C in order to mitigate the exotherm of
initial chlorination. A second stage reaction is then performed
at a higher temperature of approximately 450–500 8C to
encourage more complete fluorine for chlorine exchange. For
the purposes of this preliminary study, the reactor was operated
to emulate the first stage, lower temperature reaction. The inlet
temperature would be moderated to about 225 8C by controlling
the feeds and the outlet temperature would be allowed to
achieve 285 8C. The pressure of the reactor was held at 50 psi.
Chlorination is an extremely exothermic reaction and it is
practical to control the exotherm of reaction with a large excess
of HF. A molar ratio of HF to hydrocarbon of ꢀ30:1 effectively
controlled the exotherm for the temperatures and feed rates of
the examples. The patents recommend a chlorine to hydro-
The Du Pont patent [1] indicates that the partially fluorinated
intermediates in their process are almost all terminally
fluorinated with 1,1,1-trifluoro substitution characteristic to
each. This was verified in the products of both propane and
propene, where under-fluorinated material of the formula was
primarily 1,1,1,2,2-pentachloro-3,3,3-trifluoropropane, 4. The
under-fluorinated material of the formula C3F4Cl4 was
primarily 1,1,2,2-tetrachloro-1,3,3,3-tetrafluoropropane, 5 (iso-
mer 5a in Table 1). The under-fluorinated material of the
formula C3F5Cl3 was primarily 1,1,1,3,3-pentafluoro-2,2,3-
trichloropropane, 6. The cascade for fluorination into these
isomers is shown in Scheme 3.
2.3. Experiments on propyne and propadiene
The application of high temperature chlorofluorination
technology to acetylenes such as propyne is not a given. At the
Table 1
GC percentage of chlorofluoropropanes from chlorofluorination of C-3 hydrocarbons
Isomer formula
C3F4Cl4
Isomer
Isomer structure
Propane product (%)
Propene product (%)
Propyne product (%)
Propadiene product (%)
5a
5b
5c
5d
CF3–CCl2–CFCl2
CF2Cl–CFCl–CFCl2
CF2Cl–CCl2–CF2Cl
CFCl2–CF2–CFCl2
98
1
90.6
6.0
17.1
10.4
nd
17.2
14.6
nd
<1
nd
<1
3.4
72.2
68.0

R.K. Belter / Journal of Fluorine Chemistry 127 (2006) 1611–1615
1613
reactor. The reaction ran smoothly and chlorofluorinated
products were obtained in 76% yield. The product composi-
tion was 7% C3F5Cl3, 79% C3F4Cl4 and 13% C3F3Cl5.
Selectivity was again high for gem-difluorinated product (see
Table 1).
Scheme 3.
outset of these experiments, there were grave concerns as to the
efficacy and the safety of such a reaction. Alkynes, themselves,
are somewhat unstable. Acetylene, for example, is shipped as a
solution in acetone as it is prone to detonation in the pure form.
Acetylene, of course, is commonly used as a welding fuel.
Propyne, in its role as a welding fuel, is sold diluted with
propane and/or propene. Chloroacetylenes, especially small
molecule fluorinated chloroacetylenes, are very unstable and
detonate upon isolation. As high temperature chlorofluorination
invariably proceeds through a series of partially chlorinated and
fluorinated species, there were concerns about the possible
generation of chloroacetylenic intermediates and safety of the
proposed process. One can further diminish the prognosis for
success when one takes into account the possibility of
polymerization or carbonization of the propyne or olefinic
intermediates onto the surface of the catalyst. Experimentation
would prove that none of these concerns were to be any barrier
to performing chlorofluorination reactions on propyne (or
propadiene). Both C3H4 isomers underwent high temperature
vapor phase chlorofluorination exceedingly well under the
conditions developed in the control experiments.
Future studies are planned to increase the level of
fluorination to primarily C3F5Cl3 isomers as well as decrease
the level to C3F3Cl5 so as to determine the isomeric ratios at
those levels of fluorination. For the chlorofluorination of
propyne and propadiene, it is clear that a change in the
selectivity of early fluorination is occurring, and it is possible
that this occurs before chlorination is complete. Currently, no
monofluoro- or difluoro-intermediates have been isolated.
Insight into the early selectivity of chlorofluorination would
certainly shed light onto the selectivity for the tri-, tetra- and
pentafluorinated species. Only additional study will reveal
whether the early intermedates are mono- and difluorochlor-
opropanes or mono- and difluorohydrochloropropanes.
3. Conclusions
Despite the potential for serious side reactions, propyne and
propadiene have proven to be quite amenable to high
temperature vapor phase chlorofluorination. The yield and
extent of fluorination is nearly identical to that of propane and
propene. However, propyne and propadiene show a selectivity
for forming gem-difluoro substituted products, in contrast to the
selectivity shown by propane or propene for forming terminal
trifluoromethyl groups under these conditions.
Propyne was fed into the chlorofluorination reactor under the
same conditions used to chlorofluorinate propane and propene.
With an HF:Cl2:propyne molar ratio of 30:10:1, the reaction ran
adiabatically and the temperature of the inlet reactor zone
stabilized around 230 8C. The second, higher temperature,
reactor zone required some input of heat but was maintained at
285 8C. Total product yield was identical to chlorofluorination
of propane and propene with 70% of product being C3F4Cl4.
Yield of liquid products was 91% with 64% fluorination.
Analysis of non-condensed products mid-run showed them to
be 94% C3F6Cl2, C3F5Cl3 and C3F4Cl4 isomers. The fluorine
content of the product mixture was the same as product from
propane and propene, however the isomeric ratios for the
various fluorinated materials were markedly different than
those observed in the chlorofluorination of propane and
propene. Table 1 shows the isomeric composition of the major,
tetrafluorinated fraction.
4. Experimental
4.1. General
Anhydrous hydrogen fluoride was Matheson–Trigas CP
grade. Chlorine was Matheson–Trigas HP grade. Propyne was
98% pure from Sigma–Aldrich. Propadiene was 96% from
Synquest. Iron based catalyst was prepared by treating
commercial carbon support pellets with saturated aqueous
FeCl3 hexahydrate as per Ref. [4], Example 1. Chromium based
catalyst was prepared as per Ref. [4], Example 2, using a
chromium oxide rather than chromium chloride solution.
Chromium oxide was Baker ACS grade. GC/MS was
performed on an HP 5890/5971A spectrometer with a 60M
DB-1 capillary column. Chemical shifts of 1H (300 MHz) and
13C (75 MHz) NMR spectra were recorded in ppm downfield
from Me4Si (d 0.00) in CDCl3 using a Bruker ARX300
instrument. 19F NMR (282 MHz) were recorded in ppm
downfield from internal standard CFCl3 (d 0.00) in CDCl3.
Hydrogen fluoride was pumped directly and the flow monitored
by loss of mass from the feed cylinder. Chlorine and
hydrocarbons were flowed as vapor through a rotameter and
the flow monitored by loss of mass from the feed cylinder.
Cautionary note. Anhydrous HF causes severe burns to the
skin and mucous membranes. HF should be handled with full
PPE protection. An ample supply of HF antidote gel should be
It is clear that the selectivity for fluorination has reversed.
Whereas propane and propene generate terminally fluorinated
product (specifically, 1,1,1-trifluorinated), propyne produces
product that is internally fluorinated, with a selectivity toward
gem-difluorinated product.
In the above experiment, 98% pure propyne was used. The
allenic isomer of propyne is 1,2-propadiene. Arimura et al.
fluorinated and chlorofluorinated propadiene with chlorine
monofluoride in the presence of cesium fluoride. 1-Chloro-
2,2,3-trifluoropropane was the major product [5]. In light of
the successful chlorofluorination of propyne, it was logical to
investigate whether propadiene was as ameneable a reagent as
was propyne and to determine whether the selectivity would
remain the same. Under identical conditions to the above
experiments, propadiene was fed to the chlorofluorination

1614
R.K. Belter / Journal of Fluorine Chemistry 127 (2006) 1611–1615
kept on hand before handling HF. See the reference for burn
treatment procedures [6].
was 35:12:1. The outflow stream was condensed and collected
under pressure and upon completion of the reaction, passed into
crushed ice and separated. The clear, colorless liquid product
was analyzed by gas chromatography. Product composition was
14.4% C3F5Cl3, 69.5% C3F4Cl4 and 6.9% C3F3Cl5.
4.2. Typical catalyst bed preparation
The reactor constituted a 1 in. (2.54 cm) diameter nickel
alloy tube 24 in. (61 cm) in length fitted with a five-point
thermocouple running through the center of the reactor.
Pressure control was achieved with a teflon diaphram gas
regulator valve at the outlet end a vertical chilled water
condenser. The reactor was charged with catalyst and purged
with N2 at 200 8C until no water vapor was detectable at the
outlet with a cold mirror. Anhydrous hydrogen fluoride was
then introduced at 1 mL/min for 1 h. The temperature was
raised to the anticipated reaction temperature for 1 h. The N2
stream was enriched to 2% O2 for 2 h. The oxidant flow was
stopped and the temperature stabilized to the desired reaction
temperature. At the beginning of each reaction, anhydrous
hydrogen fluoride was flowed at 70 g/h through the previously
activated catalyst bed, maintaining an inlet reactor section
temperature of 220 8C and an outlet reactor section temperature
of 285 8C. A backpressure of 50 psi was allowed to build. After
0.5 h, a second HF flow was started at 70 g/h.
4.6. Chlorofluorination of propadiene
Into the first HF stream, propadiene was flowed at 8.1 g/h.
Into the second HF stream, chlorine was flowed at 163 g/h. The
temperature at the third (middle) thermocouple stabilized at
about 226 8C. The temperature of the last thermocouple
stabilized at 295 8C. The overall HF:Cl2:propyne ratio for the
reaction was 33:11:1. The outflow stream was condensed and
collected under pressure and upon completion of the reaction,
passed into crushed ice and separated. The clear, colorless liquid
product was analyzed by gas chromatography. Product com-
position was 7.2% C3F5Cl3, 78.5% C3F4Cl4 and 13.0% C3F3Cl5.
4.7. Spectral data (see Refs. [7–9] for literature values)
4.7.1. 1,1,2,2-Tetrachloro-1,3,3,3-tetrafluoropropane, 5a
(CFCl2–CCl2–CF3)
19F NMR (282 MHz, CDCl3): d À60.5 (q, J = 13.7, 1F,
CFCl2), À71.0 (d, J = 13.7, 3F, CF3); 13C NMR (75 MHz,
CDCl3): d 88.5 (dq, J = 38.9, 29.8 Hz, CCl2), 119.4 (d,
J = 307.6 Hz, CFCl2), 121.2 (q, J = 286.3 Hz, CF3); MS e/z
(%): 217 (100), 147 (13), 101 (20); 69 (100).
4.3. Chlorofluorination of propane
Into the first HF stream, propane was flowed at 9.8 g/h. Into
the second HF stream, chlorine was flowed at 187 g/h. The
temperature at the first thermocouple stabilized at about
230 8C. The temperature of the second thermocouple remained
at 285 8C. The overall HF:Cl2:propane ratio for the reaction
was 31:12:1. The outflow stream was condensed and collected
under pressure and upon completion of the reaction, passed into
crushed ice and separated. The clear, colorless liquid product
was analyzed by gas chromatography. Product composition was
10.4% C3F5Cl3, 83.9% C3F4Cl4 and 5.6% C3F3Cl5.
4.7.2. 1,1,2,3-Tetrachloro-1,2,3,3-tetrafluoropropane, 5b
(CFCl2–CFCl–CF2Cl)
19F NMR (282 MHz, CDCl3): d À60.5 (q, J = 13.7, 1F,
CFCl2), À64.1 (ddd, J = 21.3, 16.0, 9.9, 1F, CFCl), À121.1
(ddd, J = 16.0, 12.2, 3.8, 1F, CFCl2); 13C NMR (75 MHz,
CDCl3): d 108.5 (dq, J = 271.5, 30.7 Hz, CFCl), 117.5 (dt,
J = 312.0, 28.4 Hz, CF2Cl), 124.9 (dt, J = 304.0, 34.5 Hz,
CF2Cl); MS e/z (%): 217 (15), 132 (14), 101 (80); 85 (100).
4.4. Chlorofluorination of propene
4.7.3. 1,2,2,3-Tetrachloro-1,1,3,3-tetrafluoropropane, 5c
(CF2Cl–CCl2–CF2Cl)
19F NMR (282 MHz, CDCl3): d À58.6 (s, 4F, CF2Cl); 13C
NMR (75 MHz, CDCl3): d ꢀ88.4 (hidden, CCl2), 126.2 (t,
J = 304.7 Hz, CF2Cl).
Into the first HF stream, propene was flowed at 10.6 g/h. Into
the second HF stream, chlorine was flowed at 197 g/h. The
temperature at the second thermocouple stabilized at about
236 8C. The temperature of the last thermocouple stabilized at
291 8C. The overall HF:Cl2:propene ratio for the reaction was
30:11:1. The outflow stream was condensed and collected
under pressure and upon completion of the reaction, passed into
crushed ice and separated. The clear, colorless liquid product
was analyzed by gas chromatography. Product composition was
6.4% C3F5Cl3, 78.5% C3F4Cl4 and 13.5% C3F3Cl5.
4.7.4. 1,1,3,3-Tetrachloro-1,2,2,3-tetrafluoropropane, 5d
(CFCl2–CF2–CFCl2)
19F NMR (282 MHz, CDCl3): d À66.6 (t, J = 6.3, 2F,
CFCl2), À108.7 (t, J = 6.3, 2F, CF2Cl), 13C NMR (75 MHz,
CDCl3): d 110.7 (tt, J = 271.8, 29.9 Hz, CF2), 114.7 (dt,
J = 307.4, 36.4 Hz, CFCl2); MS e/z (%): 217 (16), 147 (9), 116
(46); 101 (100); 85 (40); 66 (50).
4.5. Chlorofluorination of propyne
Into the first HF stream, propyne was flowed at 8.7 g/h. Into
the second HF stream, chlorine was flowed at 193 g/h. The
temperature at the first thermocouple stabilized at about
236 8C. The temperature of the last thermocouple stabilizeded
at 295 8C. The overall HF:Cl2:propyne ratio for the reaction
Acknowledgements
This project was funded by Louisiana Board of Regents
Industrial Ties Grant LEQSF(2004-07)-RD-B-08, Cox-Walker
Engineering, Baton Rouge LA and Futago LLC, W. Lafayette,

R.K. Belter / Journal of Fluorine Chemistry 127 (2006) 1611–1615
1615
[3] W. Manague, M. Napa, A. Sievert, US Patent 6,018,083 (2000).
IN. NMR studies were made possible by an instrumentation
grant from The Louisiana Board of Regents LEQSF 045UG-02.
[4] Y. Iikubo, S. Owens, M. Cohn, S. Brandstadter, V. Hedrick, J. Boggs, J.
Qian, J. Sacarias, US Patent Appl. 20,040,102,660 (2004).
[5] T. Arimura, S. Kurosawa, A. Sekiya, Chem. Lett. 1 (1993) 35–36.
[6] D. Peters, R. Methchen, J. Fluorine Chem. 79 (1996) 161.
[7] T. Tanuma, K. Ohnishi, H. Okamoto, S. Morikawa, J. Fluorine Chem. 76
(1996) 45–48.
References
[1] J, Webster, E. McCann, D. Bruhnke, J. Lerou, W. Manogue, L. Manzer, S.
Sweringen, S. Trofimenko, C. Bonifaz, US Patent 5,057,634 (1991).
[2] J. Webster, E. McCann, D. Bruhnke, J. Lerou, L. Manzer, W. Manague, P.
Resnick, S.Trofimenko, US Patent 5,043,491 (1991).
[8] T. Tanuma, K. Ohnishi, H. Okamoto, S. Morikawa, J. Fluorine Chem. 84
(1997) 157–160.
[9] T. Tanuma, J. Irisawa, J. Fluorine Chem. 99 (1999) 45–48.