Note: Descriptions are shown in the official language in which they were submitted.
_ 2148752
BAYER AKTIENGESELLSCE~AFT 51368 Leverkusen
Konzernzentrale RP
Patente Konzern Gai/klu/646-PE
Process for preparin~ hexafluoro-C1 compounds
5 The present invention relates to a process for preparing hexafluoro-C4 compounds by
dehalogenative dimerization of trifluoroethane compounds in the liquid or gaseous
phase.
Hexafluol~ul~les and hexafluorobutenes are of importance as CFC substitutes and
as intermediates for preparing insecticides and acaricides (see, for example,
ro DE-A 3 818 692 and EP-A 481 182).
It is known that hexafluorochlorobutene can be prepared by subjecting chlorin~ted
butadienes to gas-phase fl~lorin~tion (see DE-A-42 12 084). This process requires the
h~nrlling of hydrogen fluoride and chlorine in the gas phase, which is only possible
with relatively large engineering expense.
Hexafluorochlorobutenes can also be prepared by pyrolysis of 1,1,1-trifluoro-2,2-
dichoroethane (see DE-A-42 14 739). A disadvantage here is that this process has to
be carried out at high temperatures. The hydrogen chloride formed requires
particularly corrosion-resistant materials for the pyrolysis reactor. Considerable
.
eng1neerlng expense lS thus necessary.
20 It is also possible to react compounds of the type CF3-CHal(Z)2, where Hal
represents chlorine or bromine and Z, independently thereof, represents hydrogen,
chlorine or bromine, with hydrogen in the gas phase over supported catalysts
cont~inin~ palladium and/or nickel and thus obtain hexafluorobutane (see DE-A-
42 12 876). A disadvantage here is that the operating life of the catalyst is influenced
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both by its qualitative and qua~ a~ive composition and also by Z. It is thus difficult
to verify reproducible conditions if the catalyst and/or the substrate is changed.
A process has now been found for preparing hexafluoro-C4 compounds of the
formula (I)
CF3-A-CF3 (I),
in which
A represents -CH2-CH2- or-CX=CX-
and
X in each case represents, independently of one another, hydrogen, chlorine,
bromine or iodine,
which is char~ct~ri7ed in that a trifluoroethane compound of the formula (II)
CF3CXYZ (II)
in which
X is as defined above, and
5 Y and Z represent, independently of one another, hydrogen, fluorine, chlorine,
bromine or iodine,
but at least one of the substituents X, Y and Z is not hydrogen
in liquid or gaseous phase is brought into contact with a metal and/or a metal
compound.
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Examples of compounds of the formula (II) which can be used are 1,1,1-trifluoro-2,2,2-trichloroethane,l ,1,1 -trifluoro-2-chloroethane,l ,1,1 -trifluoro-2,2-dichloroethane,
1,1,1 -trifluoro-2-bromo-2-chloroethane,1 , 1 ,1 -trifluoro-2-iodoethane, 1, 1,1 -trifluoro-2-
bromoethane and mixtures of these compounds.
Preference is given to using 1,1,1-trifluoro-2,2,2-trichloroethane and 1,1,1-trifluoro-
2,2-dichloroethane.
The process of the invention can be carried out in the liquid phase, for example at
temperatures of from -70 to +200C, and in the gas phase, for example at from 100
to 1200C. Preference is given to working in the liquid phase at from 0 to 200C and
in the gas phase at from 400 to 800C.
The pressure can be, for example, between 0.1 mbar and 300 bar, being selected in
such a way that the desired phase is present. Preference is given to working in the
liquid phase at pressures of from 100 mbar to 100 bar and in the gas phase at
ples~ures of from 0.8 to 5 bar, in particular at atmospheric ples~ul~. Elevated
15 pressures can be realized, for example, in autoclaves by bringing the reaction mixture
to an appropfiate temperature therein and/or ple,s.~ i7ing the autoclave with inert
gases (e.g. nitrogen or noble gases).
In the gas phase, the reaction can optionally be carried out in the presence of
diluents, in the liquid phase optionally in the presence of solvents. Suitable solvents
20 are, for example, nonaqueous polar solvents such as nitriles and ethers, in particular
acetonitrile, diglyme and triglyme. It is possible to use, for example, from 0.5 to
20 ml of solvent per 1 g of compound of the formula (II) used.
A great variety of metals and metal compounds are suitable. Preference is given to
metals and compounds of metals of the first transition group, the second main and
25 transition groups and iron, cobalt and nickel. The metals can be used, for example,
individually, mixed with one another, mixed with other metals, as alloys with one
another or as alloys with other metals. Suitable metal compounds are, for example,
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the halides, in particular the halides of the low oxidation states of the specified
metals. The metal compounds can be used, for example, as such or mixed with one
another, with other metal compounds and/or metals.
The amount of metals plus metal compounds can be, for example, from 0.1 to 10 g
5 atom equivalents, based on one halogen atom to be elimin~te~ This amount is
preferably between 0.5 and 2 g atom equivalents.
It is advantageous to use the metal and/or the metal compound in pulverulent or
otherwise finely divided form. The metal and/or the metal compound can be applied
to a support material.
10 The process of the invention can optionally be carried out under the action of
ultrasound, which is particularly advantageous when working in the liquid phase and
at relatively low pressures.
The process of the invention can be carried out batchwise or continuously.
The workup of the reaction mixture formed in the reaction of the invention can be
15 carried out, for example, by fractional distillation. If the reaction of the invention has
been carried out in the gas phase, it is advantageous to condense the gaseous reaction
mixture.
The process of the invention has the advantages that it can be carried out without
particular engineering expense, reproducible conditions can be verified relatively
20 simply even when catalysts and/or substrates change and, when the process is carried
out in the gas phase, the workup can be carried out in a simple manner.
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Examples
E2~ample 1
In a 0.7 1 enamel autoclave, 188 g of CF3CCl3 are reacted at 180C with 127 g ofcopper powder for 15 hours, with the maximum pressure occurring being 41 bar. The
5 volatile reactlon products distilled out of the residue were analysed by means of mass
spectroscopy coupled with gas chromatography. This gave a product mixture
cont~ining 83% by weight of CF3-CCl=CCl-CF3 (hereinafter referred to as DCHFB),
and also 6% by weight of unreacted starting material and 11% by weight of
chlorofluoroalkanes.
10 Example 2
In a 0.7 l autoclave, 190 g of CF3CCl3 were reacted at 100C with 44 g of iron
powder for 4 hours in 150 ml of aceloniLIile as solvent and in the further presence
of 2 g of FeCl2. The maximum ples~ule oCcllrring was 7 bar. The volatile reaction
products distilled out of the residue were analysed by means of mass spectroscopy
15 coupled to gas chromatography. The product mixture contained 9% by weight of
DCHFB and 90% by weight of unreacted starting m~t~.ri~l.
Example 3
In a 3 l autoclave, 2345 g of CF3-CCl3 were pumped into 350 g of iron powder in
1000 ml of diglyme at 180C over a period of 10 hours. The DCHFB formed was
20 simultaneously distilled off by pressure distillation in the range from 10 to 12 bar.
This gave 287 g of DCHFB having a purity, determined by gas chromatography, of
92 %.
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Example 4
In a 0.3 1 autoclave, 24 g of CF3CH2Cl were reacted at 180C with 6 g of iron
powder for 12 hours in 150 ml of diglyme as solvent and in the presence of 2 g of
FeCl2. The maximum pressure occllrring was 7 bar. The volatile reaction productsdistilled out of the residue contained 38% by weight of CF3-CH2-CH2-CF3 .
Examples 5 to 8
A vertically arranged heatable quartz tube was filled with 200 ml of steel wool.CF3CCl3 was fed in via a metering pump. After flushing with nitrogen, CF3CCl3 was
passed through the quartz tube in the amounts indicated at the le~e~;live indicated
10 telllpel~ re. The reaction mixture leaving the quartz tube was condensed at -78C
and admixed with water, whereupon an organic and an aqueous phase formed. The
organic phase was separated off, dried over sodium sulphate and analysed by gas
chromatography. Details are shown in Table 1.
Table 1
Example Temperature Weight hourly Conversion Selectivity of the
No. (C) space velocity (%) formation of
[g/l h] DCHFB (%)
600 510 12.3 94
6 550 120 17.3 91
7 600 105 24.7 92
8 650 250 39.4 59
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Examples 9 to 12
In a glass flask, 79 g of CF3CCl3 in a stream of nitrogen were reacted with 20 g in
each case of finely divided metal at from 38 to 42C in an ultrasonic bath. The
duration of the reaction was 4 hours in each case. The solid constituents of the5 reaction mixture were subsequently filtered off and the liquid phase was analysed by
gas chromatography. Details are shown in Table 2.
Table 2
Example No. Metal Mole ratio Selectivity of the formation of
CF3CCl3: metal DCHFB (%)
9 Fe 1.17 97.1
Zn 1.37 96.6
11 Mg 0.51 97.3
12 Cu 1.33 84.1
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