Process for preparing hexafluorochlorobutenes

Details Process for preparing hexafluorochlorobutenes Process for preparing hexafluorochlorobutenes

1994-10-25

1996-06-04

Siegel, Alan

Organic compounds -- part of the class 532-570 series

Organic compounds

Halogen containing

570153, C07C 1725

Patent

active

055234976

DESCRIPTION:

BRIEF SUMMARY
This application is a 371 of PCT/E093/00980 filed Apr. 22, 1993. The present invention relates to a process for preparing hexafluorochlorobutenes from trifluorodichloroethane.
Hexafluorochlorobutenes are known intermediates from which hexafluorobutanes can be prepared, these now being of interest as substitutes for chlorofluorohydrocarbons (CFCs).
It is known, from U.S. Pat. No. 2,413,695, that the pyrolysis of 1,1,1-trifluoro-2-chloroethane, a monochloro compound, leads to a saturated C.sub.4 -compound (C.sub.4 H.sub.3 ClF.sub.6).
A process has now been found for preparing 1,1,1,4,4,4-hexafluorochlorobutenes which is characterised in that 1,1,1-trifluoro-2,2-dichloroethane is pyrolysed.
The 1,1,1-trifluoro-2,2-dichloroethane required as starting material for the process according to the invention is prepared on an industrial scale and is commercially obtainable. It may optionally be used together with 1,1,1-trifluoro-2,2,2-trichloroethane.
The pyrolysis according to the invention may be performed, for example, in the temperature range 450.degree. to 750.degree. C. Temperatures in the range 500.degree. to 700.degree. C., in particular those of 550.degree. to 650.degree. C. are preferred.
The pressure is of no particular significance in the process according to the invention, as long as it is ensured that the starting material is in the gaseous state at the selected pyrolysis temperature. The pressure may be, for instance, 0.1 to 50 bar. The process is preferably performed at atmospheric pressure.
The pyrolysis may optionally be performed in the presence of inert gases, for instance in the presence of noble gases or nitrogen. However, the 1,1,1-trifluoro-2,2-dichloroethane is preferably heated to the pyrolysis temperature without any additives.
The pyrolysis may be performed in such a way that, for instance, 1,1,1-trifluoro-2,2-dichloroethane is passed into one or more tubes, made of inert material and arranged in parallel, and the tube or tubes is/are heated to the desired pyrolysis temperature. Suitable materials for the tubes are, for example, quartz, nickel and nickel, chromium or molybdenum steels. The tubes may have internal diameters of, for example, 10 to 50 mm. The length of the tube or tubes and the flow-rate of the gases may be matched to each other in such a way that the residence time in the region at the pyrolysis temperature is 0.1 to 120 seconds. The residence time is preferably 1 to 30 seconds.
The tube or tubes may optionally be filled with an inert particulate material, for instance with regularly or irregularly shaped pieces of quartz with an average diameter of 1 mm to half the diameter of the particular tube. Such inert particulate material can improve heat transfer from the heated wall of the tube to the gas flowing through.
The gas mixture emerging from the pyrolysis zone may be worked up, for example, by condensing it completely or partly and isolating the hexafluorochlorobutenes contained therein by distilling them out of the condensate together or separately from each other. In the case of a partial condensation of the gas mixture emerging from the pyrolysis zone, the fraction of gas mixture which is condensable above -78.degree. C. at atmospheric pressure, preferably above 0.degree. C., may be condensed.
The gas mixture present after the pyrolysis zone generally contains the desired products, 1,1,1,4,4,4-hexafluoro-2-chlorobutene-2 and 1,1,1,4,4,4-hexafluoro-2,3-dichloro-butene-2, which may be present, for instance, in a molar ratio in the range 35:65 to 65:35, and 1,1,1-trifluoro-2,2,2-trichloroethane, unconverted starting material, chlorine and optionally other components in small amounts.
Unconverted 1,1,1-trifluoro-2,2-dichloroethane and 1,1,1-trifluoro-2,2,2-trichloroethane may be returned to the pyrolysis according to the invention. Chlorine may be used to prepare the starting material. The hexafluorochlorobutenes obtained may together be subjected to hydrogenation to produce 1,1,1,4,4,4-hexafluorobutane, which can be used as a CFC-free blowing gas for preparing foams.
Hydr

REFERENCES:
patent: 2413695 (1947-01-01), Downing et al.
patent: 4849554 (1989-07-01), Cresswell et al.
patent: 5382720 (1995-01-01), Ikawa et al.
Journal of Fluorine Chemistry vol. 35, No. 1, Feb. 1987, Lausane CH, p. 204, Matae Iwasaki et al, `Decomposition of Some Hydrogen-Bearing Halogenated Ethanes`.

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