Preparation of dimer of fluorine-containing halo-ethane

Abstract: A dimer of fluorine-containing ethane can be obtained in a good selectivity by contacting fluorine-containing ethane of the formula: CF₃-CClX¹X² (I) wherein each of X¹ and X² is a fluorine or chlorine atom to a nickel catalyst.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a method for preparing a dimer of fluorine-containing ethane. Description of related art A dimer of fluorine-containing ethane, for example CF₃CCl=CClCF₃ is useful as a monomer of a polymer. However, a method for preparing the dimer of fluorine-containing ethane in a good selectivity is not known. US-A-2644835 discloses the coupling of non-aromatic compounds having a terminal trihalomethyl radical of the type -CX₃ where X is chlorine and/or bromine. The compounds are indicated to contain at least three coon atoms and none of the specific compounds mentioned includes fluorine. SUMMARY OF THE INVENTION An object of the present invention is to prepare a dimer of fluorine-containing ethane from fluorine-containing ethane in a good selectivity. This and other objects of the present invention are achieved by a method for preparing a dimer of fluorine-containing ethane which comprises contacting a fluorine-containing ethane of the formula: CF₃-CClX¹X² (I) wherein each of X¹ and X² is a fluorine or chlorine atom with a catalyst comprising nickel metal as such or nickel metal supported on a carrier in the presence of hydrogen gas. DETAILED DESCRIPTION OF THE INVENTION Specific examples of fluorine-containing ethane (I) are 1,1,1-trichloro-2,2,2-trifluoroethane (CF₃CCl₃, R-113a), 1,1-dichloro-1,2,2,2-tetrafluoroethane (CF₃CFCl₂, R-114a) and 1-chloro-1,1,2,2,2-pentafluoroethane (CF₃CF₂Cl, R-115). The catalyst comprises nickel. The nickel catalyst is nickel metal as such or nickel metal supported on a carrier. Specific examples of the carrier are SiO₂, Al₂O₃, activated carbon, MgO, TiO₂ and SiO₂-Al₂O₃. When nickel is supported on the carrier, an amount of nickel is 0.1 to 20 parts by weight based on the total weight of nickel and the carrier. Although a particle size of the catalyst is not critical, it is preferably from 16 to 60 mesh. The supported catalyst may be prepared by any one of known methods. An Ni/SiO₂ catalyst which contains Ni supported on SiO₂ can be prepared by, for example, adding silica Aerosil® to an aqueous solution of nickel nitrate and then evaporating the mixture to dryness. An Ni/Al₂O₃ catalyst which contains Ni supported on Al₂O₃ can be prepared by, for example, adding alumina Aerosil® to an aqueous solution of nickel nitrate and then evaporating the mixture to dryness. An Ni/C catalyst which contains Ni supported on activated carbon can be prepared by, for example, adding activated carbon to nickel nitrate, fully mixing them and then drying the mixture. Specific examples of the dimer of fluorine-containing ethane prepared according to the present invention are fluorine-containing butane of the formula: CF₃CY¹Y²-CY³Y⁴CF₃ (II) wherein each of Y¹, Y², Y³ and Y⁴ is a hydrogen, chlorine or fluorine atom, fluorine-containing 2-butene of the formula: CF₃CY¹=CY³CF₃ (III) wherein each of Y¹ and Y³ is a hydrogen, chlorine or fluorine atom, and perfluorinated 2-butyne of the formula: CF₃C≡CCF₃ (IV). A hydrogen gas is preferably used in the method of the present invention. The hydrogen gas can regenerate the catalyst. An amount of the hydrogen gas is usually from 0.5 to 10 mol, preferably from 2 to 6 mol per one mol of fluorine-containing ethane. Preferably, the reaction in the present invention is conducted in a continuous process. A feed rate of a feed gas (SV) is preferably 100 to 10,000 (h⁻¹). SV is herein defined as A reaction pressure is not limited, and any practical reaction pressure can be used. A reaction temperature is usually from 200 to 550°C, preferably from 290 to 450°C. When the reaction temperature is lower than 200°C, a conversion is low. When it is higher than 550°C, a selectivity is low and the catalyst is deteriorated. A reaction gas may be used as such, or the reaction gas may be diluted by a gas which has no effect on the reaction, such as N₂, Ar and He. PREFERRED EMBODIMENTS OF THE INVENTION The present invention will be illustrated by the following Examples which do not Limit the present invention. Examples 1 Silica Aerosil® was added to an aqueous solution of nickel nitrate and the mixture was evaporated to dryness. Then, the mixture wag dried at 120°C for one day to prepare a catalyst (Ni/SiO₂) having a nickel amount of 1 % by weight (particle size: 32 to 60 mesh). Before a reaction, the catalyst was not calcined at a high temperature. In a normal pressure fixed bed reaction apparatus (internal diameter of a reaction tube: 12.5 mm), a pretreatment for reducing the catalyst was conducted at 450°C for two hours in an H₂ stream before the reaction. A feed gas consisting of R-113a (10 cm³/min.), Ar (56 cm³/min.) and H₂ (29 cm³/min.) was fed at a flow rate of 95 cm³/min. The reaction temperature was 450°C and an amount of the catalyst was 1 g. Hydrogen halide generated by the reaction was absorbed by calcium oxide and a resultant gas was analyzed by a gas chromatography. A GC-mass Spectrometer was used so as to identify a product in a small amount. A conversion of R-113a and selectivities of resultant products after the reaction of 2 hours are shown in Table 1. Also after the reaction of 1 hour or 6 hours, the conversion was 100 % and selectivities of CF₃CCl=CClCF₃, CF₃CH=CClCF₃ and CF₃CH=CHCF₃ were high. Comparative Example 1 The procedure in Example 1 was repeated except that a Cr/SiO₂ catalyst was used instead of the Ni/SiO₂ catalyst. An amount of Cr in the Cr/SiO₂ catalyst was 1 % by weight and a particle size of the catalyst was 32 to 60 mesh. The Cr/SiO₂ catalyst was prepared by adding silica Aerosil® to an aqueous solution of chromium nitrate, evaporating the mixture to dryness and then drying the mixture at 120°C for one day. Before the reaction, the catalyst was not calcined at a high temperature. A conversion and selectivities of the products after the reaction of 2 hours are shown in Table 1. Example 1 Com. Example 1 Conversion (%) 100 27.5 Selectivity (%) R-1112 (trace) 30.5 R-1111 0 6.9 R-114a 0 37.9 R-123 0 4.3 CF₃CCl=CClCF₃ 85.8 0 CF₃CH=CClCF₃ 4.8 0 CF₃CH=CHCF₃ 6.0 0 Example 2 The procedure in Example 1 was repeated except that R-114a was used instead of R-113a in the feed gas. A conversion and selectivities of products after the reaction of two hours are shown in Table 2. Comparative Example 2 The procedure in Comparative Example 1 was repeated except that R-114a was used instead of R-113a in the feed gas. A conversion and selectivities of products after the reaction of two hours are shown in Table 2. Example 2 Com. Example 2 Conversion (%) 4.5 72.6 Selectivity (%) R-1113 0 0.6 R-1112 0 8.2 R-1111 0 10.0 R-115 0 48.0 R-112a 0 1.5 R-124 56.9 0.3 R-1110 0 3.5 CF₃CClF-CClFCF₃ 11.5 0 According to the present invention, the dimer of fluorine-containing ethane can be obtained in a good selectivity. Fluorine-containing 2-butene and perfluorinated 2-butyne which are the dimers of fluorine-containing ethane can be used as a copolymerizable monomer used for preparing a polymer having high temperature resistance and/or electrical conductivity.

Claims: A method for preparing a dimer of fluorine-containing ethane which comprises contacting a fluorine-containing ethane of the formula: CF₃-CClX¹X² (I) wherein each of X¹ and X² is a fluorine or chlorine atom with a catalyst comprising nickel metal as such or nickel metal supported on a carrier in the presence of hydrogen gas. A method according to claim 1, wherein the carrier is SiO, Al₂O₃, activated carbon, MgO, TiO₂ or SiO₂-Al₂O₃. A method according to claim 1, wherein the fluorine-containing ethane is 1,1,1-trichloro-2,2,2-trifluoroethane, 1,1,-dichloro-1,2,2,2,-tetrafluoroethane or 1-chloro-1,1,2,2,2-pentafluoroethane. A method according to claim 1, wherein the dimer of fluorine-containing ethane is a fluorine-containing butane of the formula: CF₃CY¹Y²-CY³Y⁴CF₃ (II) wherein each of Y¹, Y², Y³ and Y⁴ is a hydrogen, chlorine or fluorine atom; fluorine-containing 2-butene of the formula: CF₃CY¹=CY³CF₃ (III) wherein each of Y¹ and Y³ is a hydrogen, chlorine or fluorine atom; or perfluorinated 2-butyne of the formula: CF₃C≡CCF₃ (IV)

Inventors: IKAWA TSUNEO, MORIKAWA YUKATA, UEDA WATARU, IKAWA, TSUNEO, MORIKAWA, YUKATA, UEDA, WATARU
Applicants: DAIKIN IND LTD, DAIKIN INDUSTRIES, LIMITED
Application year: 1992
Main classification: C07C17
IPC codes: C07C17, B01J23, C07C21, C07B61