Process for preparing 1,1-dichloro-2,2,2-trifluoroethane

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 to which at least one metal selected from the group consisting of silver, copper, gold, tellurium, zinc, chromium, molybdenum and thallium is added. 1,1-Dichoro-2,2,2-trifluoroethne can be obtained in a high yield.

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 appropriate to carry out the reaction in a gas phase or a liquid 
phase. In the case of the gas phase reaction, the contact time is usually 
from 0.1 to 300 sec, particularly from 1 to 30 sec.

EXAMPLES 
The present invention will be illustrated by means of examples hereinafter. 
Example 1 
To a platinum catalyst containing 0.5% by weight of the platinum held on 
activated carbon, an aqueous solution of CuCl.sub.2 which amount 
corresponds to 1% by weight of the activated carbon was added, followed by 
the dropwise addition of 0.2 ml of formalin. The resulting mixture was 
aged at a temperature of 50.degree. C. for 5 hours. Then water in it was 
distilled off under a reduced pressure and the residue was dried at 
100.degree. C. for a day. 
18 cc of the catalyst thus prepared was packed in a SUS 316 reaction tube 
of 2 cm in inner diameter and 40 cm in length and the tube was heated by 
an electric furnace while passing nitrogen gas therethrough. After the 
predetermined temperature was reached, the nitrogen flow was stopped and 
1,1,1-trichloro-2,2,2-trifuoroethane which had been previously vaporized 
and hydrogen gas were introduced in the tube at rates of 22 cc/min. and 44 
cc/min., respectively. The reaction temperature was 110.degree. C. 
The resulting gas mixture was washed with water and dried over calcium 
chloride. Then it was analyzed by gas chromatography. The results are 
given in Table 1. 
Example 2 
In the similar method to that in Example 1, an alloy catalyst containing 
0.1% by weight of silver on the platinum catalyst in which 0.5% by weight 
of platinum had been held on activated carbon was prepared using 
AgNO.sub.3 and the reaction was carried out. The results are given in 
Table 1. 
Example 3 
In the similar method to that in Example 1, an alloy catalyst containing 
0.1% by weight of tellurium on a platinum catalyst in which 0.5% by weight 
of platinum had been held on activated carbon was prepared using 
TeCl.sub.2 and hydrogen chloride, and the reaction was carried out. The 
results are given in Table 1. 
Example 4 
In the similar method to that in Example 1, an alloy catalyst containing 
0.1% by weight of gold on the platinum catalyst in which 0.5% by weight of 
platinum had been held on activated carbon was prepared using AuCl.sub.3 
and the reaction was carried out. The results are given in Table 1. 
Example 5 
In the similar method to that in Example 1, an alloy catalyst containing 2% 
by weight of zinc on the platinum catalyst in which 0.5% by weight of 
platinum had been held on activated carbon was prepared using ZnCl.sub.2. 
16.5 cc of the alloy catalyst thus prepared was packed in a SUS 316 
reaction tube of 2 cm in inner diameter and 40 cm in length, and the tube 
was heated by an electric furnace while passing nitrogen gas therethrough. 
After the predetermined temperature was reached, the nitrogen flow was 
stopped and 1,1,1-trichloro-2,2,2-trifuoroethane which had been previously 
vaporized and hydrogen gas were introduced in the tube at rates of 12 
cc/min. and 44 cc/min., respectively. The reaction temperature was 
110.degree. C. 
The resulting gas mixture was washed with water and dried over calcium 
chloride. Then it was analyzed by gas chromatography. The results are 
given in Table 1. 
Example 6 
In the similar method to that in Example 1, an alloy catalyst containing 2% 
by weight of chromium on the platinum catalyst in which 0.5% by weight of 
platinum had been held on activated carbon was prepared using 
Cr(NO.sub.3).sub.3.9H.sub.2 O. 
16 cc of the alloy catalyst thus prepared was packed in a SUS 316 reaction 
tube of 2 cm in inner diameter and 40 cm in length, and the tube was 
heated by an electric furnace while passing nitrogen gas therethrough. 
After the predetermined temperature was reached, the nitrogen flow was 
stopped and 1,1,1-trichloro-2,2,2-trifuoroethane which had been previously 
vaporized and hydrogen gas were introduced in the tube at rates of 32.8 
cc/min. and 65.8 cc/min., respectively. The reaction temperature was 
130.degree. C. 
The resulting gas mixture was washed with water and dried over calcium 
chloride. Then it was analyzed by gas chromatography. The results are 
given in Table 1. 
Example 7 
In the similar method to that in Example 1, an alloy catalyst containing 2% 
by weight of thallium on the platinum catalyst in which 0.5% by weight of 
platinum had been held on activated carbon was prepared using TlCl.sub.3. 
13 cc of the alloy catalyst thus prepared was packed in a SUS 316 reaction 
tube of 2 cm in inner diameter and 40 cm in length and the tube was heated 
by an electric furnace while passing nitrogen gas therethrough. After the 
predetermined temperature was reached, the nitrogen flow was stopped and 
1,1,1-trichloro-2,2,2-trifuoroethane which had been previously vaporized 
and hydrogen gas were introduced in the tube at rates of 18.4 cc/min and 
36.7 cc/min, respectively. The reaction temperature was 130.degree. C. 
The resulting gas mixture was washed with water and dried over calcium 
chloride. Then it was analyzed by gas chromatography. The results are 
given in Table 1. 
Example 8 
In the similar method to that in Example 1, an alloy catalyst containing 2% 
by weight of molybdenum on the platinum catalyst in which 0.5% by weight 
of platinum had been held on activated carbon was prepared using 
(NH.sub.4).sub.6 Mo.sub.7 O.sub.24.4H.sub.2 O. 
14.5 cc of the alloy catalyst thus prepared was packed in a SUS 316 
reaction tube of 2 cm in inner diameter and 40 cm in length and the tube 
was heated by an electric furnace while passing nitrogen gas therethrough. 
After the predetermined temperature was reached, the nitrogen flow was 
stopped and 1,1,1-trichloro-2,2,2-trifluoroethane which had been 
previously vaporized and hydrogen gas were introduced to the tube at rates 
of 33.2 cc/min. and 66.3 cc/min., respectively. The reaction temperature 
was 200.degree. C. 
The resulting gas mixture was washed with water and dried over calcium 
chloride. Then it was analyzed by gas chromatography. The results are 
given in Table 1. 
TABLE 1 
______________________________________ 
Example No. 
Conversion of 113a (%) 
Selectivity of 123 (%) 
______________________________________ 
1 94 91 
2 97 96 
3 87 86 
4 93 90 
5 55 93 
6 86 85 
7 42 92 
8 50 96 
______________________________________