Organic compounds -- part of the class 532-570 series – Organic compounds – Halogen containing
Patent
1993-06-25
1995-07-18
Siegel, Alan
Organic compounds -- part of the class 532-570 series
Organic compounds
Halogen containing
C07C 2118
Patent
active
054343224
DESCRIPTION:
BRIEF SUMMARY
This application is a 371 of PCT/JP 92/01398, filed Oct. 29, 1992.
FIELD OF THE INVENTION
The pressent invention relates to a process for preparing 1,1-dichloro-2,2,2-trifluoroethane (HCFC123) which is a useful compound as a coolant, blowing agent or solvent and a raw material for compounds such as trifluoroacetic acid, HCFC124 (1-chloro-1,2,2,2-tetrafluoroethane), HFC125 (pentafluoroethane), etc.
DESCRIPTION OF THE PRIOR ART
It is known that 1,1-dichloro-2,2,2-trifluoroethane is synthesized by reducing 1,1,1-trichoro-2,2,2-trifluoroethane with, for example, zinc as a reducing agent in a protic solvent (cf. Japanese Patent Kokai Publication No. 222038/1983), with potassium acetate in the presence of an alcohol (cf. Czechoslovakia Patent No. 135722), or with sodium amalgam (cf. EP Patent No. 164954). However, all these reducing methods mentioned above have disadvantages that they are difficult to control and expensive. There are also kown methods in which reduction is effected with hydrogen in the presence of a hydrogenating catalyst (cf. Japanese Patent Kokai Publication Nos. 149739/1989, 319440/1989 and 319441/1989). The methods, however, give poor yields of 1,1-dichloro-2,2,2-trifluoroethane and hence are not the preffered methods for preparing it industrially.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a process for preparing 1,1-dichloro-2,2,2-trifluoroethane by catalytic reduction which does not cause the problems mentioned above.
Accordingly the present invention relates to a process for preparing 1,1-dichloro-2,2,2-trifluoroethane characterized in that 1,1,1-trichloro-2,2,2-trifluoroethane is reduced with hydrogen in the presence of a hydrogenating catalyst comprising platinum carried on a support to which at least one metal selected from the group consisting of silver, copper, gold, tellurium, zinc, chromium, molybdenum and thallium is added, to form 1,1-dichloro-2,2,2-trifluoroethane.
In reduction of 1,1,1-trichloro-2,2,2-trifluoroethane, particulary, in catalytic reduction, the chlorine atoms in a molecule tend to be reduced to an excess extent, resulting in a poor yield of 1,1-dichloro-2,2,2-trifluoroethane. Therefore, the inventors of the present invention have made diligent studies of methods by which only one chlorine atom in a molecule of the starting compound can be reduced and found that the intended product can be obtained in a high selectivity and a high yield by carrying out the hydrogenation reaction in the presence of an alloy catlyst comprising platinum.
DETAILED DESCRIPTION OF THE INVENTION
According to the present invention, it is important to add other metal to a platinum catalyst. In general, it is said that, in an alloy catalyst, the characteristics of component metal elements are developed depending on a composition of the alloy. The other metal is added to platinum in an amount of from 0.01 to 500% by weight, preferably from 0.1 to 300% by weight, based on the weight of platinum, to make the most of the features of platinum.
Although the concentration of an alloy which is held on a support can vary in the wide range of from 0.05 to 5% by weight based on the weight of the support, the concentration of from 0.5 to 2% by weight can be recommended.
Suitable supports used in the present invention include activated carbon, alumina, zirconia, titania, etc.
While a particle size of the support gives less effect on the reaction, it is preferably in the range of from 0.1 to 100 mm.
In the reduction of 1,1,1-trichloro-2,2,2-trifluoroethane, the ratio of hydrogen to the starting material can vary in a wide range. Usually a stoichiometric amount of hydrogen is used to remove a halogen atom. However, hydrogen may be used in much more than the stoichiometric amounts, for example, in an amount of 4 moles or more per one mole of the starting materials.
The reaction is carried out at or above atmospheric pressure. The reaction temperature is in the range of from 0.degree. to 450.degree. C., preferably from 50.degree. to 300.degree. C.
It is appropri
Koyama Satoshi
Seki Eiji
Daikin Industries Ltd.
Siegel Alan
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