CA2166024A1 - Process for the preparation of perfluoroalkyl iodide telomers - Google Patents

Abstract

Medium-chain perfluoroalkyl iodides are obtained in a good selectivity by reaction of short-chain perfluoro-alkyl iodides with tetrafluoroethylene if the telomeriza-tion reaction is catalysed by zinc, manganese, vanadium, rhenium, rhodium, ruthenium, platinum or silver.

Description

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HOECHST AXTIENGESELLSCHAFT HOE 94/F 927 Dr.KL-nu Werk Gendorf Process for the preparation of perfluoroalkyl iodide telomers Description Medium- to longer-chain perfluoroalkyl iodides are starting materials for the preparation of fluorinated surfactants and of hydro- and oleophobizing treatment materials, for example for textiles. On the other hand, n-perfluorooctyl iodide in particular is a starting material for n-perfluorooctyl bromide, which has acquired considerable importance in the medical sector.

Perfluoroalkyl iodides are prepared industrially by telomerization in accordance with the equation RfI + n F2C=CF2 ~ Rf(CF2-CF2)nI~

in which Rf is pèrfluoroalkyl having 1 to 6 carbon atoms and n is a number from 1 to about 8. The reaction is started either by heating (for example US-A 5 268 516) or by agents which form free radicals (for example GB-A 1 535 408 or US-A 5 068 471). Perfluoroalkanes are formed to a considerable extent in the thermal reaction by dimerization of the perfluoroalkyl radicals intermedi-ately formed, and hydrogen-containing compounds occur as by-products in the free radical reactions.

As can be seen from the abovementioned reaction equation, the formation of the generally undesirable longer-chain telomers is suppressed by a high concentration of the telogen RfI. Selectivity in the direction of the desired medium-chain telomers is therefore paid for by low conversions, with which a high expenditure on distilla-tion of telogen to be recycled and low-chain telomers is associated.

In a publication called a ~Preliminary Note~, Chen et al., Journal of Fluorine Chemi~try 36 ~1987), page~ 483 to 489, describe the use of eopper a~ a telomerization catalyst. This proeesQ has the advantage that the reae-tion already proeeeds at 80 to 100C and require~ ~horter reaetion timeQ in relation to high-temperature telomer-izations. Relatively large amount~ of undesirable longer-chain telomer~ are still formed in the reaetion of perfluoroethyl iodide and tetrafluoroethylene in a molar ratio of 1:2 to 2:1.

It has now been found that other metal~ a~ eataly~ts increase the selectivity of the telomerization reaction in the direetion of the de~ired medium-ehain produet~
without this having to be paid for by lower eonversions.
Since quantitative comparison~ with metal catalyst~ are diffieult - the same aetive surface area would have to be always guaranteed - it can be said at least for the preferred embodiments of the invention that it has al~o been possible to increa~e the ~electivity further with increased conversions.

The invention relates to a proce~ for the preparation of perfluoroalkyl iodide telomer~ of the formula Rf~cF2-cF2)nI ' in which Rf is perfluoroalkyl having 1 to 6 carbon atom~
and n i~ a number from 1 to about 4, the maximum number of carbon atoms in the resulting telomer mixture being in the range from 6 to 10, by reaction of a perfluoroalkyl iodide of the formula RfI, in which Rf has the above-mentioned me~n; ng, with tetrafluoroethylene, whieh compriQes employing zinc, manganese, vanadium, rhenium, rhodium, ruthenium, platinum or silver a~ the cataly~t.
Preferred embodiments of the invention are explained below in more detail:

The metals used as the cataly~t can be employed in finely divided form a~ a powder or on an inert or at best weakly 2166024 ~

active supports. Other metals, such as iron, cobalt, nickel, chromium, molybdenum, tungsten, titanium or mixtures thereof, can also be used as the inert or weakly active supports. Autoclaves in which the reaction space is lined with such a metal can thus be coated with a catalytically active metal.

Mixtures of the catalytically active metals mentioned can of course~also be employed according to the invention.
Advantageous are on the one hand cheap active metals such as zinc or manganese. However, a relatively high amount of these metals is necessary and, furthermore, they lead to a certain amount of perfluoroalkanes [by dimerization of radicals Rf(CF2-CF2) n- ] . Therefore, noble metals are preferred such as the relatively cheap and active silver which do not show these disadvantages and which show a long activity as catalysts.

Preferred telogens are 2-iodoperfluoropropane, and l-iodoperfluoroethane, -butane and -hexane. It has been found that the rate of reaction when 1-iodoperfluoro-butane and -hexane are employed is about 1.6 times higher than with l-iodoperfluoroethane. A preferred embodiment of the invention thus comprises employing these lower telomers as telogens - in the pure form or as mixtures.

Since the reaction according to the invention is multi-phase - the gas tetrafluoroethylene is reacted with the liquid telogen over a solid catalyst - good thorough mixing is to be ensured. Supported catalysts in which the metal combinations are applied to a support of relatively low density are therefore advantageous, since the float-ability in the liquid perfluoroalkyl iodide phase isimproved in this way. The use of a stirrer through which the tetrafluoroethylene is gassed into the liquid phase is furthermore advantageous. So-called jet reactors in which the liquid phase is pumped in circulation via a nozzle together with the catalyst are also favorable. The gas - in this case tetrafluoroethylene - is metered in 2~6602l _ 4 -shortly before the nozzle. The high shearing forces generated in the nozzle cause effective gas/liquid transition. These reactors are also suitable for con-tinuous operation.

In an advantageous embodiment of the invention the catalyst is placed into a tube reactor, for example of stainless steel, which is provided with an inlet, a temperature control for heating and cooling and, at the outlet, with a pressure control. The educts, perfluoroalkyl iodide and tetrafluoroethylene, are fed in at the inlet. Depending on the telogen, for example 1-iodoper-fluoroethane or l-iodo-n-perfluorobutane, the internal pressure is adjusted in a manner that the perfluoroalkyl iodide predominatly remains li~uid during the reaction by adjusting the pressure in a range of 8 to 18 bar.

It has furthermore been found that water - if oxygen is excluded - does not lead to an increased formation of by-products and also impairs the reaction only a little.
It is thus not necessary to dry the starting materials.

Further preferred embodiments of the invention can be seen from the following examples.

Examples The results were evaluated by gas chromatography, direct evaluation of the data found in the form of parts by weight being obtained by means of experimentally cali-brated area factors.

Before use, the perfluoroalkyl iodides employed were freed from impurities such as hydrogen fluoride or iodine with potassium carbonate powder and were stored under nitrogen. Purity determined by gas chromatography:

,~
F2C=CF2 99.98%
n~C2FsI 97-5%
n-C4F9I 99.8%
n C6F13I 98.7%
i C3F7I 99.5%

Examples 1 to 13 The reactions were carried out in a 300 ml rocking autoclave of high-grade steel (V4A, material 1.4571). The stated amount of catalyst was initially introduced into the autoclave under nitrogen. After a trial pressure with 50 bar of nitrogen, the autoclave was evacuated to 1 mbar and then cooled to -78C. After the stated amount of perfluoroalkyl iodide had been sucked in, the desired amount of tetrafluoroethylene ("TFE" in the tables) was condensed in at -78OC (weighing must be performed rapidly in order to avoid errors due to icing up of the autoclave).

Examples 1 to 3 and Comparison Example Vl 50 g of l-iodopentafluoroethane were shaken in the stated molar ratio with tetrafluoroethylene with the stated amount of catalyst at 100C for 5 hours. The results are shown in Table 1. The sum of all the non-RfI compounds is totalled in the last column under ll~ X~'. In the evalu-ation by gas chromatography, these compounds were weighted globally with the weight factor 1.00. They are, for example, tetrafluoroethylene, RfH compounds (which are contained in the educts in a small amount), per-fluoroalkanes and water (which was introduced into the system during metering of the samples with a cooled syringe).

Table 1 Ex. CatalystMolar ratio ProdUCt di~tribution C2F5 (CF2-CF2) n~I [% by weig ]

tg] [n~nol] O 1 2 3 4 5 6 7, 8 9 10 ~ X
Vl Cu 2.0 31.5 2.2263.411.9 7.25.33.9 2.9 1.91.0 0.4 --- --- 2.1 V l.0 19.6 2.2260.412.8 8.35.83.9 2.6 1.71.0 0.5 0.2 0.1 2.7 2 Mn 2.0 36.4 2.2265.112.2 7.34.73.1 1.9 1.20.7 0.4 0.1 --- 3.3 3 Rh 0.1 0.97 2.074.87.34.93.62.61.7 1.1 0.60.2 0.1 --- 3.1 .
Examples 4 to 7 and Comparison Example V2 Analogous to the preceding examples, 69.2 g of 1-iodo-n-perfluorobutane were employed here and the batch was again shAk~n at 100C for 5 hours. In Example 6, the catalyst comprised 0.5 ml of water. In Example 7, the silver was employed as a supported catalyst with 10% by weight of silver on aluminum oxide.

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216602l g Examples 8 to 11 69.2 g of 1-iodo-n-perfluorobutane were shaken with tetrafluoroethylene in the stated molar ratio with 2.0 g of zinc (30.6 mmol) at various temperatures for 5 hours.
More detailed data and the results are shown in Table 3.

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Examples 12 and 13 98.5 g of l-iodo-n-perfluorohexane were shaken with the stated catalyst and tetrafluoroethylene in the stated molar ratio at 100C for 5 hours. Nore detailed data and the product distribution are shown in Table 4.

To improve clarity, the following example has also been included in Table 4.

Example 14 The same reactants were reacted analogously to Example 13 in a glass flask equipped with a stirrer, thermometer and condenser and having a valve set at 130 mbar gauge at the top end. The tetrafluoroethylene was passed into the flask in the course of 3 hours. The total reaction time was 5 hours and the temperature was 110C-.

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216602l Examples 15 to 17 86S g of 1-iodo-n-perfluorobutane were reacted in a molar ratio of 2:1 with tetrafluoroethylene with the stated catalysts and at the stated temperature in a 1 l stirred S tank. The stirred tank was eguipped with a sheath for the thermocouple and an anchor stirrer ~maximum speed 350 rpm). The results are shown in Table 5.

Examples 18 to 20 The reaction was carried out analogously to Examples lS
to 17, but with a gassing stirrer, the tetrafluoro-ethylene being fed in through the hollow stirrer shaft and being swirled into the liquid phase in the form of fine bubbles via fine bores at the end of the stirrer blades. The gassing stirrer had a maximum speed of lS SOO rpm. Further data and results are likewise shown in Table 5.

The reaction time was 5 hours for Examples lS to 17 and 2.5 hours for Examples 18 to 20.

Table 5 Ex. Catalyst Temperature Product distribution C2F5(CF2-CF2)n-I ~% by weightl, n =
lgl [mmoll ~Cl 1 2 3 4 5 6 7 8' ~ X
15 Zn25.0 38290 to 100 74.6 12.8 3.8 1.1 0.30.1 2.3 16 Mn27.5 500 110 78.5 11.3 3.5 1.0 0.20.1 5.4 17 Zn25.0 38295 to 100 63.4 18.9 6.7 2.2 0.70.3 2.2 +Ag 0.5 4.6 18 Zn 15.0 229 90 51.1 28.512.5 4.4 1.30.3 0.1 1.8 19 Mn 15.0 273 100 52.5 27.511.6 3.8 1.20.3 0.1 3.0 20 Zn 10.0 153 90 50.7 28.812.8 4.0 1.20.4 0.2 0.1 1.8 +Ag 0.2 1.8 Example 21 29.6 g (0.1 mol) of perfluoroisopropyl iodide and 5.0 g (0.05 mol) of tetrafluoroethylene were reacted with 1.0 g of zinc (15.3 mmol) at 80C in the autoclave mentioned for Examples 1 to 13 for 3 hours. The product distribu-tion is shown in Table 6.

Table 6 Example Product di~tribution (CF3)2CF(CF2-CF2)n-I l% by we g ], 0 1 2 3 4 5 6 7 8 9 ~ X
21 57.1 18.0 11.4 6.3 2.9 1.4 0.7 0.4 0.2 0.1 1.5 - 17 _ 2166024 Examples 22 to 29 In a 250 ml rocking autoclave two series of experiments were performed: Series A consisting of Examples 22 to 26 and 8eries B consisting of Examples 27 to 29. The following catalysts were tested (percentages by weight):
10 % of silver on Al2O3 2 % of palladium on Al2O3 1 % of platinum on Al2O3 2 % of rhenium on Al2O3-SiO2 5 % of ruthenium on Al2O3 5 % of rhodium on active charcoal In each case 0.2 mol of 1-iodo-n-perfluorbutane were reacted with 0.1 mol of tetrafluoroethylene and 1 mol-%
of metal, related to 1-iodo-n-perfluorobutane, for 5 hours at 100 C.

In test series A the commercial form of catalyst was used without any additional activation. In series B silver and rhenium were not tested since they are highly active without activation. The other catalysts had been activated for series B as follows:

1 mol-% each, related to 1-iodo-n-perfluorobutane, of catalyst was treated in a 250 ml autoclave with 10 bar of hydrogen and 10 bar of nitrogen during 5 hours at 160 C.
After releasing the pressure the autoclave was rinsed with nitrogen and the catalyst was after-treated for 30 minutes with 20 bar of nitrogen in order to remove any adsorbed hydrogen. After cooling to room temperature the autoclave was evacuated and the reaction was started. The results are shown in Table 7.

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Claims (4)

1. A process for the preparation of perfluoroalkyl iodide telomers of the formula Rf(CF2-CF2)nI , in which Rf is perfluoroalkyl having 1 to 6 carbon atoms and n is a number from 1 to about 4, the maximum number of carbon atoms in the resulting telomer mixture being in the range from 6 to 10, by reaction of a perfluoroalkyl iodide of the formula RfI, in which Rf has the abovementioned meaning, with tetrafluoroethylene, which comprises employing zinc, manganese, vanadium, rhenium, rhodium, ruthenium, platinum or silver as the catalyst.

2. The process as claimed in claim 1, wherein the catalytically active metal is fixed to a support.

3. The process as claimed in claim 1 or 2, wherein the metal is silver.

4. The process as claimed in one or more of the preced-ing claims, wherein the tetrafluoroethylene is gassed into the liquid phase with a stirrer.