Note: Descriptions are shown in the official language in which they were submitted.
~ 162~11
-- 2 --
The presen-t in-~entlon relates -tc a process for
the selective preparation o~ 2-chlo~o-1,1,1,~,3,~,3-
heptafluoro-propane ("2~chloro-heptafluoroprop~ne") by
photochlorination of 1,1,1,2 3 3,3,3--heptafluoropropane
("2H-heptafluoropropane").
2~Chloro-heptafluoropropane (boiling point
-2C) belongs to the category of the completely halo-
genated alkanes, which is distinguished by exceptional
thermal and chemical stability, non-flammability and
special electrical and other physical properties.
2-Chloro-heptaf]uoropropanecanbe ernployed,inter alia, as
a coolant or heat transfer medium, as an inert sol~ent-
or cleaning agent for low temperature use, as a gasecus or
liquid inert medium, for example as a dielectric or
insulating medium, as a fire-extinguishin~ agent or
additive to fire~extinguishing agents, or as an etchan-t
for silicon dioxide layers on silicon. In the patent
literat-ure, 2~chloro-heptafluoropropane has been pro-
posed as a blowin~ agent or blowing agent componen-t
(U.S. Patent 4,057,973), and for the preparation of sol-
uble, fusible polymers of :low flammability from more
easily fla~mable polymers by irradiation (Ge man Paten-t
1,213,117). Accordingly, there is considerable
interest in a simple and economical process, which does
not pollute the environment, for the preparation of the
compound shown in the title.
2-Ch~oro-heptafluoropropane has already been
described repeatedly in the litera-ture. Most pro-
cesses for its prepara-tion are based on -the :~luorination
~.
of a C3-compour.d:
~ lUS~ accordin~ toU S.Patent 2,466,i89, the com-
poundCF~CCl~CF3 canbe obtairledby fluorinating 2-chloro-
pentafluoropropene with hydrogen fluoride and l~ad
diox de in an au-toclave, whilst according to British
Patent 839,0~4 it can be obtained by an addition reac-
tion of elementary fluorine with 2-chloro-pentafluoro-
propene. The fluorination of l,l,l-trifluoro-tri-
chloropropene by means of cobalt trifluoride, in accord-
ance with U.S. Pa-tent 2,670,387 also produces 2~chloro-
heptafluoropropane, in low yield.
The fluorination of 3-chloro-prop-2-ene with
hydro~en fl~loride at temperatures above 500C, in
accordance ~ith the process of U.S. Patent 3,047,6~
results i.n a yield of about 50~6 of the title compound.
According to U.S. Patent 2,831,035, -the reaction of
fluorlne or of chlorine trifluoride with CF3CC12CClF2
or CF3CC12CC12F in the presence of an aluminum fluoride
catalyst ~esults in the formation of no-t only octa-
fluoropropane but also 2-ch]oro-heptafluoropropane.
On a labo.ratory scale, the title compowld can
be prepared in yields of over ~0% by an addi.-tion reac-tion
of chlorine fluoride with hexalluoropropene (D. D.
Moldavski.~ Y. G. Temchenko e-t a]., Zh. Org. Khim. ~,
2~ 673)- Howevel, transfer of this process -to an indus-
trial scal.e is difficul.t, since by-products which are
difficult to separate off are for~ed and the chlorine
fluoride employed is highly toxic, is awkward -to handle,
since, for exa~ple9 it reacts vigorously with glasr; and
2~
e~plosively with hydrogen-containing compounds, and
must~ furthermore, in its turn be prepared from ~le--
mantary fluorine and chlorine.
None of the known processcs is suitable for
the selective preparation of 2-chloro-heptafluoropropane
in high yields. ln all the processes, fragmentation
reactions or other competitlve reactions occur to a con-
siderable degree. The undesired by~products reduce
the yield and make extensive distillation operations
necessary. Furthermore, the known methods of pre-
paration require starting compour.ds which are difficult
to obtain, ~meconomical fluorinating agents or high
reaction temperatures, which resu]t in increased cor-
rosion of the reactor materials and short lives of
catalysts.
Accordingly, there existed the problem o:~ pro-
viding a sil~ple process for the selective preparation
of 2 chloro-heptafluolopropane, which is based on
easily accessible starting materials and proceeds with
high yields.
This problem is solved by the invention defined
in the main claim.
The process according to the inven-tior can be
operated continuously in the manner of conventional
gas/gas reactions. A solid catalyst is not required
for -this purpose. The preferred -tempera-hlre range
is from 20 to 450C, especially from 30 to 400C, and
more particularly from 4-0 to 350C.
~ igh-energy light means, in the present context,
~ 5 -
radiatio-n w~lich is capable of decomposing chlorine
molecules in-to chlorine atoms, in particular visible
light and ultraviolet ligh-t in the range of from 450
to 260 nm. The process according to the invention
can be described by the equation
CF3-CH~-CF3 ~ C12 ~ CF -CClE'-CF + HCl
The reaction can be carried out in a corven-
tional irradiationapparatus, such as is used, for
example, for chlorinating toluene to give benzyl
]o chloride. Such an apparatus consistsS for e~ample,
of a glass flask into whlch a mercury high-pressure
immersion lamp provided with a quartz tube is in-tro-
duced. The glass flask is additionally equipped ^rith
a gas inlet tube, an internal thermometer, a condenser
~Jhlch is cooled with carbon dioxide1 and a drainage
stopcock attached to the bottom. The glass flask
should be capable of being externally heated at the
level of theimmersion lamp and a-t the level of the
drainage stopcock.
In general, the meterèd gaseous starting pro-
ducts are ir.-troduced as a mixture into the glass flask.
m e gas mix-ture leaving the reactor is washed with
wa-ter, whereby hydrogen chloride formed is absorbed.
Thereaf-ter, the residual ch]orine is rernoved with thio-
sulfate solution and dilute sodium hydroxide solution
and -the produc-t is dried by means of -towcrs which are
Iilled wi-th calcium chloride or with phosphorus pen-t-
- oxide. The crude product can be condensed in suitable
cold traps.
1 ~2~11
The boiling points of starting materials and
end products are summarized in the -table below:
Product or Formula Molecular Boiling
material weight point/
1 bar
... . . .
2H-Heptafluoropropane CF3CHFCF3 170.03 -18C
Chlorine C12 70.96 -34.1
Hydrogen chloride HCl 36.46 -~5
2Cl-HeptafluoropropaneCF3CClFCF3 204.47 -2
. . .
m e 2H-heptafluoropropane emplcyed is of
technical-grade purity and is advantageously anhydrous,
ie. it is preferably clried with phosphorus pen-to;~ide.
2H-Heptafluoropropane is easily obtainable b~r the
quantitative addition reaction of hydrogen fluoride
with hexafluoropropene, for example in accordance with
German Offenlegungsschrift 2,7]2,732. Chlorine is
taken from a commercial steel cylinder and is advan-
tageously employed in the anhydrous form, ie. it is
dried with, for example, concentrated sulfuric acid.
The conversion of 2H-heptafluoropropalle at
300 and atmospheric pressure is abou-t 0.1 to 3 moles/l
of reactor volume per hour, depending on the radiation
intensity. Lower throughputs are readily achieva~]e.
At higher pressures, the conversion can be correspond-
ingly higher. In generals the chlorine is added
without ~ilution; the amount of ch]orine is in general
between 0.1 and 3.5 moles/l of reac-tor volume per hour.
The amo~mt ofshlorine shouldbe at leas-tequivalent to the an~ount
Of 2H-heptafluoropropan~ which is added simul+aneously
J1~2511
-- 7 --
and contjnuously. A slight excess of chlorine is
preferred. The molar ratio of 2H-heptafluoroprop~ne/
chlorine is, for example, be-tween 1 : 1.5 and 1 : 1,
preferably bet~Yeen 1 :1.15 and 1 : 1.05. Quantitat-
ive conversion of ~H-heptafluoropropane can be achieved
by uslng an excess of chlorine. Whilst larger
excesses of chlorine are feasible, they are no-t advan-
tageous, since, if an efficient condenser is used, there
is the danger that unconverted chlorine liquefi~d in
the condenser and flowing back into the irraclia-tion
reactor may lower the temperature in the reactor and
accordingly lead to a reduction in the rate of r~action.
Furthermore, the excess of chlorine increases the
effort en-tailed in wor~ing up by distillation. Any
maJor excess of chlorine is advantageously removed ~rom
the ~aseous reaction products by fractional distil-
lation; the recovered chlorine can be re-used.
Whilst it is possible to employ a less than equival~nt
amount of chlorine, this reduces the conversion and
increases the effort entailed in working up.
In general, the process is carried ou-t without
addition of an inert gas. Whilst dilution with an
iner-t gas, such as, for examp]e, ni-trogen, is ~easible,
i-t does not offer any significan-t advantages.
The irradiation reac-tlon can be carried out
over a wide tempera-ture range, of from 30 to ~500C;
however, the reaction proceeds only slowly in the range
of Irom -30 to -~l~0C. Accordingly, temperatures
- above 40C are preferred. ~,~ils-t temperatures in the
~1~;251~
range oI from 350 -to 500C are fcasible they are dis-
advantageous from the point of view of energy
consumption.
The residence time o~ the starting materials
and of the end products in -the reac-tor is not critical;
it can, for example, vary bet~een a few seconds and a
few minu-tes, without the composition of the crude pro~ j
ducts being adversely affected by the occurrence of
side-reactions or secondary reactions. On -the other
hand, econornical considera~ions impose an upper limit
on the residence time. Accordingly, it is advantage-
ous, for a high space--time yield, that the reaction
products formed should be removed trom the reactor as
promptly as possible.
~he hydrogen chloride formedisin general dis-
charged at the top, through a condenser cooled with
solid carbon dioxide. ~le 2-chloro-hep~afluoropro-
pane formed, which collects at the bottom of the
reactor, can also be taken off continuously, through a
stopcock.
The process according to the invention is in
general carried out under a-tmospheric pressure, but the
use of reduced pressure or superatmospheric pressure
(for eY.ample up to 10 barS preferably up to 3 bar) is
also possible, within wide limits. In order to
achieve high space-time yields, it is preferred to use
superatrnospheric pressureO
For reac-tions on an industrial scale, a continu-
ous and uniform method of opeiation is desirable. In
'~ 162~11
~ 9 _
the process accc,rding to the invention, continuous
introduction of chlorine and 2H-~heptafluoropropane,
continuous conduct of the reaction, continuous dis-
charge of the reactlon products and continuous working
up are readi.ly possible. Further particular advan--
tages of the conti.nuous procedure are the improved
utilization of the s-tarting materials and the small
amount of effluent and waste gas produced.
..In the process according to the invention, the
conversion of 2H-heptafluoropropane is in general abcve
90% and often above 99jo.
Because of the high selec-tivity of the process
according to the invention, the yields of 2-chloro-
heptafl.uoropropane are also above 90,~ and often above
98% of theory. The 2-chloro-heptafluoropropane pro--
duced i.s obtained in high purity. Workin~ up is
therefore extremely simple.
In view of literature statements concerning the
lack of reactivity towards chlorine of hydrogen atoms
in the immediate vicinity of tri.fluorome-thyl groups, it
is surprising -that the subs-titution of hydrogen by
chlorine in 2H-he~afluoroprop.lne proceeds so s~noothly
in the process according to the invention.
It is known tha-t in comparable compournds such
as C~3~CrI2-CF3 and CF3-CH--CF~, hydrogel~ is no-t replaced
CCl~ -
by chlorlne (Houben-Weyl 5 Methoden der organi.schen
Chemie (~ethods of Or~anic Chemistry), 1962~ volume
V/3, pages 59/l-598).
1A ~; 2 5 1 ~
-- 10 -
'rhe process is illustra-ted by the Examples
which follow.
Example 1
r~le experimental arrangement consists of a
mu]ti-neck irradiation flask made of~ DURAN glas.s,
which has a capacity of 2 liters and into which an
ultraviolet high-pressure mercury i~nersion lamp pro-
vided with a thin-walled quartz glass tube is intro-
duced. m e irradiation flash is additionally
equipped with a gas i.nlet tube, which terminates near
the in~ersion lamp, an internal thermometer, which
extends into the vicinity of the immersion lamp, a con-
denser filled with solid C02, which is placed on one
of the ground-glass connections attached to the top,
and a drainage stopcock located at the bo-ttom of the
irradi.ation flask. l~e outer walls can be addition-
ally heated externally,by means of electrical radian-theaters,
at the level of the immersion lamp and a-t the level oI
the drainage stopcock. Both the upper exi-t o.f the
condenser and the exit of the drailnage cock lead to a
wash vessel, fil.led wi.th water, to take up the hydrogen
chloride formed. m ese wash vessels are followed by
wash vessels filled with aqueous lO~o strength Na2S203
solution to take up the excess chlorine5 and vessels
filled with aqueous lO~o strength NaOH for the final
wash. m ese are then followed by two drying towers,
one filled with CaC12 for pre-drying and the other
filled with ~25 ior final drying. The gaseous crude
prod.uc-t is fillally condensed in a high efficiency cold
~ 3
trap, cooled ~ith C02
Elel~entary chlorine is taken from a cor~,ercial
steel cylinder, dried with concentrated H2S04, metered
by means of a flowme-ter and mixed with the stream of
5 CF3CI-IFCF3 gas.
2H-Heptafluoropropane is prepared in accordance
with German Offenlegungsschrift 2,712,732, by hydro-
fluorination of hexafluoropropene in the presence of a
chromium oxyfluoride catalyst. I-t is dried with
P205, metered by means of a flo~eter and mixed with tne
stream of C12.
BefoIe starting the photochlorination, the reac-
tion chamber, which has beforehand been flushed with N2,
is pre-heate~ by switching on the ultraviolet lamp;
this results in temperatures of about 150 to 180C in
the reactor chamber. In the immediate vicinity of
the immersion lamp, tempera-tures of 260 to 300C are
measured on the quartz glass.
To pho-tochlorinate 2iI-heptafluoropropane, a tot;al
of 76 g (0.45 mole) of CF3C~IFCF3 and 33 g (0./i6 mole) of
ch~orine, corresponding to a molar ratio of
CF3CIIFCF3: C12 of 1 : 1.02, is introduced in -the course
of 2 hoursi at temperatures of 120 to 90C. During
the e~periment; the hydrogen chloride evolved which is
not retained by the condenser is absorbed in the wash
water receiver. After completion oI`-the reaction,
flushing with N2 is employed in order to wash -the entire
hydrogen chloride into the wash water. In the pre-
sent example (1) the other gaseous reaction p-oduc-ts,
i 1~251 1
-- 12 --
which collect at the bot-tom of the irradlation vessel,
are discharged through the drainage stopcock, located at
the bottom, onl-~ after completion of the reaction.
0.44 mole of HCl is found, by titration, in the
wash water; HF is not found. m e condensed crude
product is examined by gas chromatograph~ on a ~ PORAPAK
c~lwnn. This reveals the following:
CF3CCl~CF398.1%
CF3CHECF3 1.7%
CF3CClFCClF2 0.1%
c~3cF3 ~ 0-05%
CF3CF2CF3< 0.05%
The two last-mentioned components are uncon~
verted impurities of the heptafluoropropane employed;
CF3CClFCClF2 is produced by chlorina-tion of C3F6, which
is also present in traces in the starting material.
The liquid crude product weiglls 88 g. Accord-
ingly the yield of CF3CClFCF3 is 95.4% of theory, based
on CF3CHFCF3 conver-ted. The 2-çhloro-1,1,1,2,3,3,3-hepta-
fluoropropane is addi-tionally identified by 19F-NMR
measuremen-t, infrared recordings and determination of the
boiling point, which is -2C.
Example 2
CF3CHFCF3 is photochlorinated, at tempe~atures
of 115 -to 110C at the beginning of the experiment and
temperatures of 35 -to 20C at the end of the experiment,
by passing into the apparatus of Example (1), in the
course of 5.5 hours, a total of 467 g (2 75 moles) of
CF3CHFCF3 and 198 g (2.79 moles~ of C12, corresponding
1 1~2~1 1
-- 13 --
to a molar rat:o of CF3CHFCF3 : C12 of 1 : 1.01. The
condensed reacti.on produc-ts which collect at the bot-tom
of the irradiation flask are, as in Example (1), removed
via the drainage s-topcoc~s only after completion of the
experiment, and are then washed.
1.84 moles of HCl are found by ti-tration in the
wash water of the gases. Ana.lysis by gas chromatog-
raphy reveals the following composi.-tion of -the condensed
crv.de product:
CF3CClFCF3 67.5%
CF3CHFCF3 32.1%
3 other components each 0.1%
The condensate weighs 512 g. m e yield of CF3CClFCF~
i~ accordin~ly 90.5% of theory, based on CF3C~FCF3 con-
verted; however, the conversion of CF3C}IFCF3 is onlyabout ~8~.
A total of 495 g (2.91 moles) of CF3CHFCF3 and
217 g ~3 06 moles) of chlorine, corresponding to a molar
ra-tio of CF3CHFCF~ : C12 of 1 : 1.05, are introduced as
gas, in the course of 5 hours, into the apparatus of
Examp]e (1), a-t temperatures of 120 to 110C, which can
be mai.ntained over the entire experiment. m e reac
ti.on products whlch collect are discharged con-tinuously
and uniformly via the drainage stopcock, locateda-t-thebot-
tom of-theirradia-tion ~lask, excep-tfor acons-ta.ntly remaining
residua~ amoun-t of about 10 to 15 ml, and are then
~ashed.
2.76 moles of HCl ~re found in the wash wa-ter of
5 ~ J
_ 14 -
~the gascs. Gas chromatography rneasurements on the
collected condensed crude product show the following
composition:
CF3CC] FCF395 3%
CF3CHFCF33~ 9%
Remainder: secondary
components 0~8%.
m e condensate weighs 585 g. Accordingly the yield
of CF3CClFCF3 is 97.6% of theory, based on CF3CEJFCF~
converted.
Example 4
A total of 1,080 g (6.35 moles) of CF3CHFCF3
and 526 g (7.41 moles) of chlorine, corresponding to a
molar ratio of CF3CHFCF3 : C12 of 1 : 1.17, is int;ro-
duced, in the course of 7.5 hours, into the apparatus
of Example (1), at t~mperatures of 135 to 125C. The
outer walls of the flask are additionally heated, at the
level of the immersion lamp and of the drainage stop-
cock, by means of electrical radiant hea-ters. ~s in
Example (3), -the reaction products which collect are
discharged continuously and uniformly from the flask.
6. 31 moles of HCl are foun~l in the wash ~a-ter.
.nalysis by gas chromato~raphy reveals -the fol:Lowing
composition of the crude product:
CF3CClFCF399. 7%
CF3CHFCF30.15%
CF3CClFCClF2< 0.025'
CF3CF2CF3~ 0,05%
CF3CE~FCClF~0.1~6
.
2 5 1
-- 15 --
The condense~te ~-eighs 1,289 g; accordi.ngly the yield of
CF3CClFCF3 is 99.1% of theory, based on CF3CHFCF3 con
verted. The conversion of CF3CIIFCF3 is 99.85% of
theory,
.
