Note: Descriptions are shown in the official language in which they were submitted.
0~5
Processes for the mallufacture of fluorocarbon compo~mds
are al eady known. US paten~ 2,519,983 doscribes t~e electro-
chemical manu~acture of fluorocarbon compounds at a cell
. . . ~ , , .
voltage of about 4 to ~ volts direct current, a current
densi~ of up to about 20 m ~/cm2 and at a temperature of-20C to
~0C, prefera~ly 0C to ~20 C, in liquid hydrogen fluoride as
; electrolyte The application of a higher voltage is not re-
co~nended since energy is lost a~d at the same time no im-
provement in yield is attained. Further, long-chain carbon
A compounds are more b~gb~ fragmented simulta~eously with the
, : .
addition of fluorine, i.e a great number of compounds with a
; lower number of car~on atoms than those of the starting compound
are formed. The electrochemical fluorination of carboxylic acid
halides and sulphonic acid halides forms the subject matter of
US patents 2,717,871 and 2,732,398. The conditions for carry-
ing out the process correspond to the state~ values, i.e. the
; process is carried out for example at a cell voltage of about
4 to 6 volts direct current. Likewise only unsatisfactory yields
are obtained with long-chain starting products, since molecular
fragmentation~ optionally combined with cyclisation reactions,
occur during the reaction. Consequently, the yields of tri-
; fluoromethanesulphochloride are about 55 % (T. Gramstead and
R.N. Hazeldine, J.C.S. 173 (1956) report 96 %) and of perfluoro-
octanesu'phochloride 25 % [cf. T,Gra~stead and R.N. Hazeldine,
, 25 J.C.S. 2640 (1957)], whereas J.Burdon et al., J.C.S. 2574 (1957)
~`~ obtain only about 12 % to 15 %.
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A further process for the electrochemical fluorination is
known from German Auslegeschrift 1468284. By the choice of the starting
compounds, the attempt is made to improve both the selectivity of the
; electrochemical reaction and the yield. The process, which is carried out
under the cited conditions (potential of about 4 to 8 volts), is confined
to a special group of starting compounds some of which are not readily
accessible. The yields are only good in respect of short-chain molecules,
whereas e.g. in the manufacture of C8Fl7S02F only yields of less than 20%
were obtained.
The present invention provides an improvement of the process
for the electrochemical fluorination of organic acid halides, in particular
of long-chain acid halides, by using - in contrast to the prior art - a
: substantially higher cell voltage while at the same time optionally increas-
ing the current density. The temperature range for carrying out the
: electrochemical fluorination has also been modified. Surprisingly, the
- yield of fluorinated acid halides and the purity of the end products are
substantially improved in the process according to the invention while at
the same time improving the current yield. The formation of molecular
fragments with fewer carbon atoms than the starting material, the occurrence
~' 20 of any side reactions and the formation of only partially fluorinated
, products can be very largely avoided. Further, the corrosion of the anode
material is materially reduced.
The present invention therefore provides a process for the
electrochemical fluorination of alkylcarboxylic acid halides or alkyl- -~
sulphonic acid halides of 5 to 18 carbon atoms using an anode of nickel or
a nickel alloy, a metal cathode and liquid hydrogen fluoride as electrolyte,
which comprises electrolysing the organic acid halides in an amount of 5 to
.
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20 percent by weight, based on the electrolyte, at temperatures of 20C to
; 50C, and at a cell voltage of 9 to 15 volts direct current, the distance
between the electrodes being 6 to 12 mm, and subsequently separating the
fluorinated products from the electrolyte.
Suitable organic acid halides are normally alkylcarboxylic
~ acid and alkylsulphonic acid halides with 5 to 18, preferably 6 to 12 or
; 8 to 10, carbon atoms in the alkyl moiety. Acid chlorides and, in
particular, acid fluorides are preferred. They have e.g. the formulae
: '
(1) 3 ( 2)m
and
(2) 3 ( 2)n 2 '
.,
` wherein X represents fluorine, chlorine or bromine, m is an integer from 3
to 16, preferably from 4 to 10 or 6 to 8, and n is an integer from 4 to
- 17, preferably from 5 to 11 or 7 to 9. Preferred acid fluorides are also
those of the formulae
'
3 2 m
and
( ) CH3 (CH2)n S02F,
.....
~,
wherein m is an integer from 4 to 10, preferably 6 to 8, and n is an integer
from 5 to 11, preferably from 7 to 9.
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Examples o organic acid halides are hexanoic-, octanoic-,
decanoic- or ~odecano;icsulpl~oni_ acid halides, in par~icular
. ~he sulphonic acid fluorides.
These acid halides are mixed with the liquid hydrogen
fluoride in an amount of about 5 to 20, preferably 5 to 15 or
10 to 15 % by wei~ht before the start of the eLectrochemical
fluorination. Col~nercial anhydrous liquid hydrogen fluoride
: which normally contains a trace of water is used as electrolyte.
- In contact with a humid atmosphere, the hydrogen fluoride
moreover takes up water. The bulk of this water can be removed
r~ ~ by a preliminary electrolysis that is carried out before addi-
j. .
tion of the starting materials. The water is removed by hydrogen,
; oxygen and oxygen fluoride (OF2), all of which escape in gaseous
.
form.It is not necessary to add conductivity salts. e.g. potas-
:r
~ 15 sium fluoride, to the electrolyte, since this causes increased
. . .
corrosion of the electrode material. Moreover, the el-ectrolyte
retains its conductivity, even after termination of the ~;~
fluorination, so that the conclusion of the reaction is only
inadequately detected. ;
The electrochemical fluorination is carried out at tem-
peratures between 20 C and 50CJ preferably between 30 C and
~0 C. The best yields are obtained at about 30C to 35 C. The
process is ordinarily carried out at normal pressure or at an
- overpressure of up to about 5 ba~,preferably up to about 1 bar.
The cell voltage is 9 to 15, preferably 9 to 13 or 9 to
12 volts willtout any dev~lopment of fluorine gas being observ-
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ed. The ~oltage theoretlcally necessary or the manufacture of
free fluor:ine (~2) from hydrogen fluoride is about 3 volts
(US patent 2,S19,9~3~. Lf it is possible to apply higher
voltages without the development of fluorine gas according,
the reason is that a substantial amount of the voltage is used
up for overcoming the resistances that are formed through the
electrolyte, the ele~trodes and especially througll polarisation
, . .
effects at the electrode surfaces.
The electrodes are spacecl about 6 to 12,pre~erably 8 to
10 mm apart. These relatively large spacings made it possible
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for example to markedly reduce the corrosion of the electrodes
and the danger of a short-circuit reaction between the electrodes.
The current densities can be in the approximate range
A from 10 to lO0 ffl-A/cm2, preferably in the range from 20 to
60~/cm , whereby it is possible to attain current
~; yields of over 50 %. Although the reaction mechanism has not
~,,,;,. . .
been fully clarified and the present invention is not limited
by any specific reaction mechanism, it is assumed that in the
electrochemical fluorination described herein a loose, active
complex of different nickel fluorides and molecular or atomic
fluorine is first formed at the anode. The acid halide adsorbed
on the com~lex is then com~letely reacted, then the current
densitiy falls to a fraction of the initial value and thereby
- indicates the end of the electrochemical fl~orination.
Support for this possible reaction mechanism is to be
found in the fact that practically no partially fluorinated
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prGducts are formed and that there is no visible formation
of flt~oline gas, since free fluorine (F2) from the active
complex carl also be used for the fluorin~tion. It can further
., .: .
be observed that the corrosion of the anodes (ater an in-
duction period using new anodes) is very slight, which can be
a~trib-uted to the formation of a protective layer of nickel
, fluorides.
Preferably nickel or a nickel alloy is used as anode
:~ .
material for the process according to the invention;but
10 optionally it is also possible to use anodes of silicon
carbide or charcoal. Suitable cathodes are iron or steel
cathodes, also those of e.g. aluminium~ copper, nickel or ;~
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nickel alloys.
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- The electrochemical fluorination can be carried out ;
batchwise and optionally also semibatchwise by replenishing
both the organic compo~md and the hydrogen fluoride electroly~e
from time to time in the same amount in which they are used up
and separating the perfluorinated products which are insoluble
~ in hydrogen fluoride from the electrolyte and removing them
- 20 from the cell.
The escaping gas mixture can be led through an ascending `
coole~ in order to condense the hydrogen fluoride vapours, then
after dilution with an inert gas it is absorbed in dilute sodi~m
hydroxide solution.
The perfluorinated compounds obtained are valuable ;~
starting materials for the manufacture of oil and water re-
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pellents, sur.EacLants, lubricants and the like. The end produc~s
are obtai.ned by modification the acid halidc gro~lping b~ kno~
chemic~ reac~ions. Further, they can also be used by themselves
.~. as surfactants.
The following Examples describe the.invention ir. more
`.~ detail but do not limit it to what is described therein.
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-'; Example ]
_ ~ufacture o~ f orc)oc~yls~ c _cid fluoride
The reaction is carried out in a~ electrolysis cell of
nickel with a capacity for 40 ml of liquid hydrogen fluoride
and provided with a nickel anode (0.35 dm surface area), a
thermometer, an inlet pipe for ~he acid halide and the liquid
hydrogen ~]uoride as well as an exhaust gas pipe cooled to -15C
which is sparged with nitrogen in order to prevent the formatio
- of explosive gas mixtures and to produce a desired pressure ,~
(under which the electrochemical reaction proceeds) in the
~, cell. The cell is in a thermostat. ~t the start of the reaction,
the cell is cooled to -~10 C, then the liquid hydrogen fluo~ide
(-10C) and octanesulphonic acid fluoride are charged into
the c-eil.
, The cell is then heated with thethermostat to the desired
temperature. The nitrogen pressure is about 0.6 bar overpressure
at 35 C. Upon termination of the reaction, the cell is again ' ~'
conled to a temperature of ~10 C and brought to normal pressure. ;`
~` The fluorinated reaction product is insoluble in liquid hydrogen
.:
,'~` 20 fluoride and precipitates as a colourless oil on the bottom of
the cell. The oil is isolated and washed with 10 % aqueous ;"
sodium hydrogen carbonate solution. Thepurity of the product
is normally 90 to 95 % (analysis by gas chromatography)~ The
.- . :.,- .
indicated yields are calculated on the oily end product with a ''
content of at least 90 % per-fluorooctylsulphonic acid fluoride.
, The following table contains the test conditions and results:
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...... . . . . .. .. .. ..
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3 ~41()35
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e~periment l 2 3 4 5 6 (comp ri~so~i~
:: ~ ~ ~ _.--
; ten-perature ( C) 32 34 32 30 32 20
. _ . __ . _. .. ,.. __ _
amoun~ by octane-l
. suLpllo~uoride ~1 4 4 4 4 4 4
: ~_ _ ..... ~ . . __ ___ .
concentration
. in % 10 10 10 ]S 10 10
: ~relative to the
l -electrolyte~ .
. " _ _~
~; potential volt 1 9 9 10.5 ].2 12 7
- A cUrrent densi~y ~.025 .. 0~.020 . 0~050 0~056 0~056 0~.01
cCoun~ru~nlpttion~ ~ .6 lS.6 18.6 18.6 18.6 18.6
(theoret.)
... _ , ... . . ._~
current I '
consumptiOn Ah ~15 16 1-2 13 13 20
~4~ (actual) ~
. .. .. ~ . . ._ __ ..... . . _ _ ~_
current ~. . .
. consump~ion re- 81. 86 65 70 70 llO -
: ferred ~o tne tl~eo ~. .
retical va~ue (%)
:: ~ ...... ~
current yield (%~ 50 50 72 87 81 27
.; . _ ........ : . .___ __ ,
product yield (~) ¦ 3~4 3~.6 3~9 5~ 8
prod~ct yield (%) ¦ 4l 43 ~7 6] 57 30
.. .
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.,
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i(135
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Experimenk ~ was carried out under the conditions of ~he
. prior ar-k. The yield obtainecl is markedly lower than the yields
; that are obtained with tlle process according to the invention.
.
Example 2
Perfluor~ ation of n-heptane-l-car~o~rlic acid fluoricle
.... . _
(octanoic fluoridc) ~
. .
At 0C, 20 parts of anhydrous hydrogen fluoride are
charged into the electrolysis cell according to Example l and
then 3 parts of n-heptane-l-carboxylic acid fluoride are added
thereto. The contenks are electrolysed under a nitrogen over-
pressure of 1 bar at 30Cj a cell voltage of lO volts and an
initial current density of 0.037 A/cm . The electrolysis is
- discontinued when 80 % of the theoretical amount of current has
been consumed.
, 15 Yield: 2.65 parts of a crude oil with 87 V/~ content of -
perfluorinated compound. The oil is purified as described in ;;
Example 1. The yield is 37 a/a of theory.
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