Process for preparing hexafluoropropanone-2

#The present invention relates to a process for preparing hexafluoropropanone-2. More particularly, it relates to a process for preparing hexafluoropropanone-2 from hexafluoropropene with a high efficiency by the use of a specific catalyst.

#Hexafluoropropanone-2 is useful by itself as a catalyst for polymerization of perfluorocyclobutene or triazine. Because of its polymerizability, it forms a terpolymer with tetrafluoroethylene and ethylene. It is also useful as the starting material for the production of bisphenol AF ((C.sub.6 H.sub.4 --OH).sub.2 C(CF.sub.3).sub.2) which is an excellent crosslinking agent for fluorine-containing elastomers.

#For production of hexafluoropropanone-2, there is known a method which comprises oxidizing hexafluoropropene and subjecting the resultant 1,2-epoxyhexafluoropropane to rearrangement to obtain hexafluoropropanone-2. For example, hexafluoropropene and oxygen are contacted with activated silica gel at a temperature of 140.degree. to 280.degree. C to obtain 1,2-epoxyhexafluoropropane, which is then subjected to rearrangement in the presence of a Lewis acid such as aluminum oxide to give hexafluoropropanone-2 (U.S. Pat. No. 3,775,439). Thus, in the conventional method, two steps of reaction are required for the production of hexafluoropropanone-2.

#1. preparation of catalyst:

#In a reaction tube made of Pyrex glass (28 mm in diameter, 1000 mm in length) and vertically set up in an electric furnace, there is charged granular activated alumina having a particle size of 2.3 to 4.7 mm (alumina gel; "Neobead C-4" manufactured by Mizusawa Kagaku Co., Ltd.) (51.25 g). Dehydration is effected under heating at 500.degree. C for 1 hour in nitrogen stream, and then the temperature is lowered to 200.degree. C. The supply of nitrogen is stopped, and a mixed solution of CCl.sub.4 and CF.sub.2 ClCFCl.sub.2 (1 : 1 in molar ratio) is introduced at a rate of 1 g/min from the top of the reaction tube. The upper part of the alumina layer shows immediately a raise of the temperature up to 270.degree. C. The zone of high temperature is gradually moved to the lower layer, and after 40 minutes, an equilibrium is attained whereby the whole alumina layer shows a temperature higher than the designed temperature by about 10.degree. C. Then, the designed temperature is raised to 250.degree. C. In this case too, there is caused a slight hot spot which moves to the lower layer with lapse of treating time and, after 45 minutes, passes the lowest layer. Further, the designed temperature is raised up to 300.degree. C, whereby the raise of temperature is hardly shown. After the treatment for 40 minutes, the furnace is allowed to cool, and the catalyst is taken out. The thus obtained catalyst having a fluorine content of 9.9% by weight is designated as "catalyst I".

#The preparation of the catalyst is effected in the same manner as mentioned above under the following conditions to obtain the catalysts designated as "catalyst II" and "catalyst III".