Patent GB-581662-A (GB)
Title: Improvements in or relating to the manufacture of organic fluorine compounds
IPC: C07C17/20
Filed: 1944-10-04
Abstract: Trihalomethyl ethylenes containing at least one fluorine atom in the trihalomethyl group are prepared by reacting a trihalomethyl ethylene, as hereinafter defined, in which at least one of the halogen atoms in the trihalomethyl group is a halogen other than fluorine, with a fluorinated methane in the presence of a Friedel-Crafts catalyst at a temperature of at least 100 DEG  C. The expression "a trihalomethyl ethylene" means an organic compound of the general formula X3C-CY=CY2 in which the X substituents are halogen atoms and Y is hydrogen or halogen. Thus the starting materials comprise compounds of the above general formula in which the X substituents are halogen atoms at least one being a halogen other than fluorine and Y is hydrogen or halogen; such compounds include those containing the groups: <FORM:0581662/IV/1> <FORM:0581662/IV/2> <FORM:0581662/IV/3> , <FORM:0581662/IV/4> <FORM:0581662/IV/5> , and <FORM:0581662/IV/6> ; for example, hexachloropropylene, 1.1.3.3.-tetrafluoro - 1.2 - dichloropropylene, 1.1.1.3.3. - pentachloro - 2 - fluoropropylene, 1.1.1.2.3 - pentachloropropylene and 1.1.1.3.3-pentachloropropylene may be used; the preferred compounds are those in which there is at least one halogen atom attached to at least one of the doubly bonded carbon atoms. Specified fluorinated methanes are dichlorodifluoromethane, dichlorofluoromethane, chlorofluoromethane, chlorodifluoromethane, bromodifluoromethane, difluoromethane, chlorotrifluoromethane, fluorotrichloromethane, trifluoromethane, and tetrafluoromethane. The Friedel-Crafts catalysts may be chlorides or bromides of polyvalent metal cations including such salts as aluminium chloride or bromide, ferric chloride, zinc chloride and stannic chloride; they are employed, preferably in amounts corresponding to from 0.1 to 20 per cent by weight of the materials used.  The process may be carried out continuously or intermittently.  Additional fluorinated methane may be added during the reaction.  The reaction may be carried out in a closed system in the liquid or vapour phase or in the vapour phase by passing the mixed vapours of the reactants through a hot reaction tube containing the catalyst.  The reaction is carried out, preferably, at temperatures between 100 DEG  and 200 DEG  C. and generally at superatmospheric pressure; preferably, water should be absent. The products have the general formula FnX(3-n)C-CY=CY2, where n is a positive integer of from 1 to 3, X represents a halogen other than fluorine and Y hydrogen or a halogen; generally, a mixture of fluorinated products is obtained in which n is 1, 2 and 3, the products being separable by fractional distillation.  The halogenated methanes obtained as bye-products may be reconverted into fluorinated methanes by known methods and recycled.  In the preferred form of the invention the trihaloethylene, for example, hexachloropropylene and the fluorinated methane, for example, chlorodifluoromethane and an amount of anhydrous aluminium chloride within the range of 0.1 to 20 per cent of the weight of reactants, are heated with agitation in a silver-lined autoclave for several hours at 100 DEG  to 200 DEG  C. Two examples are given illustrating this process in which hexachloropropylene and chlorodifluoromethane yield the following products: CF2-CCl=CCl2, CF2Cl-CCl=CCl2, CFCl2.CCl=CCl2 and chloroform.  The Specification as open to inspection under Sect. 91 relates to the treatment, as above, of trihaloethylenic compounds containing the grouping <FORM:0581662/IV/7> the X substituents being halogen atoms at least one of which is a halogen other than fluorine and the double bond being a linkage in an aliphatic chain or in an alicyclic ring and which, preferably have the general formula X3C-CY=CY2 where Y represents hydrogen, a halogen or a monovalent alkyl radical such as methyl, ethyl, isobutyl, amyl, hexyl and cyclohexyl radicals, the reaction being carried out at elevated temperatures.  This subject-matter does not appear in the Specification as accepted.