DE1768657A1 - Process for the preparation of 1,1,1-trifluoro-2-bromo-2-chloroethane - Google Patents

Description

Patent attorneys Dipl.-Ing. R Weickmann,

D1PL.-ING. H. Weickmann, D1PL.-PHYS. Dr. K. Fincke

_HM y D1PL.-ING. FAWeICKMANN, DiPL.-ChEM. B. HUBER

8 MUNICH 27, DEN

Gase 12 592-F möhlstrasse 22, phone number «3921/22

THE DOW CHEMICAL COMPANY, Midland, Michigan / V. St. A.

Process for the preparation of 1,1,1-trifluoro-2-bromo-2-

chloroethane

The invention relates to a process for the preparation of 1,1,1-trifluoro-2-bromo-2-chloroethane by reacting 1,1,2-Triiluor-2-chloroethylene and hydrogen bromide in the vapor phase in the presence of activated carbon and aluminum chloride or Aluminum bromide as catalysts.

The one produced by your method according to the invention Product CF., CHBrCl is a valuable inhalation anesthetic and there have been numerous methods of making it suggested. For example, US Pat. No. 2,921,099 describes a process for the preparation of trifluorobromochloroethane by fluorination of 1,2-dibromo-i, 1,2-trichloriitnane with HP in the presence of an antimony fluoride catalyst. the

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U.S. Patent 2,849,502 shows the production of 1,1,1-rrifluoro-2-bromo-2-chloroethane by high-temperature vapor-phase chlorination of 1,1,1-trifluoro-2-bromoethane, and U.S. Patent 2 921 098 shows the manufacture of the same products » by high-temperature vapor-phase bromination of 1,1,1-trifluorine-2-chloroethane. However, these known methods are not entirely satisfactory. For example, all undesired by-products in these processes, which are difficult to separate and which reduce the yield of the desired "product"

The disadvantages of the previous processes have been overcome by the process according to the invention for the preparation of 1,1, t-trifluoro-2-bromo-2-chloroethane, which consists in that 1,1,2-trifluoro-2-chloroethylene with hydrogen bromide at a - Temperature of 70 to 150 ⁰ C in the presence of activated charcoal and an aluminum halide in the vapor phase is implemented

The inventive process is carried out in the vapor phase at a temperature of 70 to 150 ⁰ G, a reaction temperature of 115-135 ° C is usually preferred. Lower temperatures are not sufficient to keep the Heaktion participants in the vapor phase, and therefore do not give the advantageous results of the inventive method

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driving. In general, higher temperatures should be avoided as they can cause degradation or partial decomposition of the halocarbons during the reaction and therefore provide undesirable by-products.

In the vapor phase and at the specified reaction temperature, a mixture of hydrogen bromide and 1,1,2-trifluoro-2-chloroethylene is brought into contact with activated carbon and aluminum chloride or aluminum bromide (referred to here as aluminum halide). It is usually best to contact the reagents with a mixture of activated carbon and aluminum halide. Optionally, however, the reagents may first with activated carbon and then with the Aluminlmhalogenid either at the reaction temperature or at a lower temperature, eg, · between about 30 and about 7O ⁰ C, are brought into contact also with reaction temperature.

To a practically complete conversion of 1,1,2-trifluoro-2-chloroethylene in 1,1, i-trifluoro ^ -bromo ^ -chloroethane To achieve without the formation of significant amounts of by-products, the reagents are preferably used with the activated carbon and the Aluminum halide catalysts for a total of 10 to 60 seconds with contact times of 20 to 35 seconds usually giving the best results. If so the catalysts are used separately rather than in the form

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a mixture of activated carbon and aluminum halide, the reagents must work with the activated carbon during a greater proportion the total contact time. The additional reaction that occurs when the reagents interact with the activated carbon are in contact is relatively slow compared to the almost instantaneous rearrangement reaction that results with the aluminum halide. It is usually desirable to have virtually anhydrous reagents and catalysts to be used in the method of the invention. Due to the capacity of activated carbon to absorb gaseous substances, it is usually also advantageous to saturate the activated carbon catalyst bed with gaseous hydrogen bromide before the 1,1,2-trifluoro-2-chloroethylene is introduced into the reactor.

It was found beneficial to maintain at least a small molar excess of hydrogen bromide over 1,1,2-trifluoro-2-chloroethylene during the reaction. An oil ratio of hydrogen bromide to CF ₂ = CFG1 between 1.1: 1.0 to 1.2: 1.0 has proven to be particularly suitable. The reagents are kept in contact with the catalysts at the reaction temperature for a sufficient period of time in order to achieve a practically complete conversion of 1,1,2-trifluoro-2-chloroethylene into 1,1,1-trifluoro-2-bromo-2-chloroethane The pressure has no critical influence on the reaction and atmospheric pressure is therefore usual.

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borrowed the cheapest. TJm to shorten the response time, can however, self-pressure or a higher pressure can be applied.

After the reaction, the product from the reactor occurs in gaseous form and can be cooled, aur removal of excess hydrogen bromide and especially free halide with water and dilute NaOH washed, then dried and used as virtually pure 1,1, "l-trifluoro-2-broni 2-chloroethane. For many purposes the product can be used directly without further purification. However, if a higher degree of purity is required, the removal of traces of impurities can easily be achieved by conventional methods such as distillation. "

The product so made is a useful and reactive chemical intermediate, but it is special useful as an inhalation anesthetic.

example 1

A silicon reactor tube (V ^ ycor) with high purity 1.90 cm in diameter and 76.2 cm in length was measured to 61.0 cm in length with 175 cubic inches of dried activated charcoal with one particle size packed from 0.84 to 1.65 mm. A second reaction tube of 1.90 cm in diameter and 30.5 cm in length, which contains 50 cm of AlCl-,

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on glass wool was attached immediately downstream of the first reaction tube. The reactors were ^{heated to 100 0} G and hydrogen bromide was passed through for 4 hours in order to remove all traces of water, to saturate the catalyst beds and to convert the AlGl to AlBr.

At the end of this period, the first reactor was ^{heated to 125 to 130 0} C and the second reactor cooled to 70 ⁰ C and a flow of 150 cnr / min CF ₂ -CClP and 190 cnr / min hydrogen bromide fed to the reactor, so that a Total contact time of 28 seconds. The gaseous product emerging from the reactor was washed out with water, condensed, dried and examined by infrared spectrogram and nuclear magnetic resonance. These analyzes indicated that the product consisted of essentially pure CF, CClBrH.

Example 2

In a manner similar to that described in Example 1, a single catalyst bed with a volume of 225 cm was packed with a catalyst consisting of 30% by weight of AlCl on 70% by weight of activated carbon. The bed was heated to 125 to 130 ^° C. and saturated with hydrogen bromide. 1 hour was then a mixture which 48 g (0.41 mol) of CP ₂ = CClP and 43 g (0.53 mol) of hydrogen bromide, fed to the reactor at a

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Contact time of '29 seconds after the end of the experiment 74 g of product collected, corresponding to a yield of 93% by weight. Infrared spectroscopic analysis of the product showed that ee consisted of 100 $ CF ^ CHBrCl.

Example 3

A 1.90 χ 7612 cm Vycor tube was packed with a 30.5 cm bed of dry activated carbon from 0 «9i to 1.65 mm, on top of which a 30.5 cm long bed of AlCl, to 0.84 to 1.65 on activated carbon as support folgtet the reactor was heated to 130 ^{0 (-} heated, saturated with hydrogen bromide and then 0.266 mole of CF ₂ ⁰ CCLP and 0.32 mole of hydrogen bromide were sent in such a way through the reactor, that first contact with the activated carbon and then with the carrier-containing AlCl. The contact time with the activated carbon was 48 seconds and with the carrier-containing AlCl, 24 seconds. An organic yield of 0.243 mol (91 | 5 # of theory) was achieved. The infrared spectroscopic analysis showed that this Material consisted entirely of the CF, CHBrCl isomer and gas-liquid chromatographic analysis showed that the material consisted of 99% by weight of CP ₅ CHBrCl.

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Claims (3)

-B- claims 1. A process for the preparation of 1,1,1-trifluoro-2-bromo-2-chloroethane, characterized in that 1,1,2-TrIfIuOr-S-ChIOräthylen with hydrogen bromide at a temperature of 70 to 150 ⁰ C in the presence τοη activated carbon and an aluminum halide are implemented in the vapor phase. 2. The method according to claim 1, characterized in that a molar ratio of hydrogen bromide to CF ₂ »CFC1! Between 1.1» 1.0 and 1.2j 1.0 is used. 3. The method according to claim 1 or 2, characterized in that gaseous 1,1,2-trifluoro-2-chloroethylene and hydrogen bromide first with the activated carbon at a temperature «between 70 and 150 ⁰ C and then with an aluminum halide at a temperature between 30 and 70 ⁰ C are contacted. 4. Process according to one of Claims 1 to 3, characterized in that the activated carbon is mixed with gaseous hydrogen bromide is saturated before the 1,1,2-trifluoro-2-chloroethylene in the Reactor is initiated. 10M4I / 1I12 BAt) ORIGINAL