US005254772A United States Patent (19) 11) Patent Number: 5,254,772 Dukat et al. (45) Date of Patent: Oct. 19, 1993 (54) CHEMICAL PROCESS FOREIGN PATENT DOCUMENTS (75) Inventors: Wolfgang W. Dukat, Konigstein, Fed. Rep. of Germany; John H. 705927 3/1965 Canada ................................ 570/170 Holloway, Leicester; Eric G. Hope, 0164798 12/1985 European Pat. Off. Warwickshire, both of England; Primary Examiner-Alan Siegel Matthias Rieland, Hanover, Fed. Attorney, Agent, or Firm-Cushman, Darby & Cushman Rep. of Germany; Paul J. Townson, Lancashire; Richard L. Powell, 57) ABSTRACT Cheshire, both of England A process for the preparation of an alkane containing fluorine by contacting a halogenated alkane containing 73) Assignee: Imperial Chemical Industries PLC, at least one hydrogen atom and at least one halogen London, England atom selected from chlorine, bromine and iodine with a (21) Appl. No.: 849,604 transition metal fluoride selected from osmium hexaflu oride, iridium hexafluoride, rhenium hexafluoride, ru (22) Filed: Mar. 12, 1992 thenium pentafluoride, chromium pentafluoride, vana (30) Foreign Application Priority Data dium pentafluoride, rhenium heptafluoride and uranium Mar. 12, 1991 GB United Kingdom ................. 9105167 hexafluoride, whereby to replace at least one hydrogen atom or at least one chlorine, bromine or iodine atom in 51 Int. Cl. ....................... CO7C 17/20; CO7C 17/00 said halogenated alkane starting material by a fluorine 52 U.S.C. ..................................... 570/170; 570/123 58) Field of Search ........................ 570/170, 168, 123 atom. Use of certain of the defined transition metal fluorides, 56) References Cited e.g. Osf6, Irfs and ReF6 allows the selective replace U.S. PATENT DOCUMENTS ment of halogen by fluorine, while others, e.g. UF6, 2,423,045 9/1943 Passino et al. VFs and ReF, allow selective replacement of hydrogen 2,759,026 2/1950 McCleary . by fluorine. 3,235,608 3/1962 Gibbs. 3,972,953 8/1976 Lyons . 8 Claims, No Drawings 5,254,772 1 2 The proportions of halogenated alkane and transition CHEMICAL PROCESS metal fluoride are not critical; either may be in excess over stochiometric, if desired. Thus, for example, the This invention relates to a process for the fluorination proportion of halogenated alkane to transition metal of aliphatic compounds, and more particularly to a 5 fluoride may be in the range from about 50:1 to about process for the replacement by fluorine of at least one l:50, and preferably in the range from about 20:1 to hydrogen atom and/or at least one halogen atom other about 1:20 of the stoichiometrically required propor than fluorine in aliphatic compounds. tion, although these ranges are given merely by way of It is already known to manufacture aliphatic com guidance and are in no way limiting on the process of pounds containing fluorine by reacting aliphatic chloro O the present invention. Hydrogen fluoride may also be carbons or chlorohydrocarbons with fluorinating included in the reaction mixture as a fluorinating agent, agents such as antimony pentafluoride. In many cases, the metal fluoride then optionally being employed in a however, known fluorinating agents do not give en catalytic amount. tirely satisfactory results, being somewhat deficient in In operating the process of the invention, whether at activity and/or in product selectivity. 15 least one hydrogen atom or at least one halogen atom It has now been found that certain transition metal other than fluorine, or both hydrogen and halogen in fluorides are useful fluorinating agents capable of selec the halogenated alkane is/are replaced by fluorine may tively replacing by fluorine one or more hydrogen depend to a large extent on the particular halogenated atoms and/or one or more halogen atoms other than alkane and on the particular transition metal fluoride fluorine in aliphatic compounds. 20 used. According to the present invention there is provided Where it is desired to replace at least one halogen a process for the preparation of an alkane containing atom in the halogenated alkane, the preferred transition fluorine which comprises contacting a halogenated metal fluorides are Oss, Irf6 and ReF6. The use of alkane containing at least one hydrogen atom and at these particular fluorides allows the replacement of 25 halogen atom other than fluorine in the halogenated least one halogen atom selected from chlorine, bromine alkane by fluorine with a selectivity which may be as and iodine with a transition metal fluoride selected from high as 80% and even as high as 95%, in particular osmium hexafluoride, iridium hexafluoride, rhenium where Oss is used. w hexafluoride, ruthenium pentafluoride, chromium pen Where it is desired to replace a hydrogen atom in the tafluoride, vanadium pentafluoride, rhenium heptafluo 30 halogenated alkane and the halogenated alkane is a ride and uranium hexafluoride, and replacing at least chlorinated alkane, the preferred transition metal fluo one hydrogen atom or at least one one chlorine, bro rides are UF6, VFs and ReF7. The use of these particu mine or iodine atom in said halogenated alkane by a lar fluorides allows the replacement of at least one hy fluorine atom. drogen atom by fluorine with a selectivity which may Halogenated alkanes which may be employed in the 35 be as high as 80% and even as high as 95%, in particular process of the invention may contain one or more car where UF6 is used, bon atoms, for example, typically up to 6 carbon atoms, Furthermore, certain of the transition metal fluorides, and have at least one hydrogen atom and at least one for example Rufs, may selectively replace at least one replaceable halogen atom selected from chlorine, bro hydrogen atom in certain halogenated alkanes, for ex mine and iodine. Other atoms, for example fluorine, ample CF3CH2Cl, yet selectively replace at least one may also be present. halogen atom other than fluorine in other halogenated Especially useful halogenated alkanes include hydro alkanes, for example in dichloromethane. CrFs may chlorocarbons and chlorofluorohydrocarbons. selectively replace at least one hydrogen atom although Specific examples of halogenated alkanes which may the selectivity may be better with certain halogenated be used include dichloromethane, chlorofluorome 45 alkane starting materials than with others; for example thane, dibromomethane, bromofluoromethane, and 2 high selectivity is obtained with CrFs for the replace chloro-1,1,1-trifluoroethane from which the products ment of hydrogen in CFCH2Cl although selectivity may be respectively difluoromethane, and 1,1,1,2-tetra may not be as high with CH2Cl2. In addition, ReF may fluoroethane. selectively replace at least one hydrogen atom where In operating the process of the invention, the haloge the halogenated alkane is a chlorinated alkane, but may nated alkane may be contacted with the transition metal selectively replace at least one halogen atom where the fluoride at a temperature at which the halogenated halogenated alkane is a brominated alkane. alkane is in the liquid phase or the vapour phase but The process of the invention is of particular value for conveniently the liquid phase. Accordingly the temper the preparation of difluoromethane from dichlorometh ature may be from about -80 to about 25' C. depending 55 ane or chlorofluoromethane and accordingly in a pre upon the boiling point of the halogenated alkane, al ferred aspect of the invention there is provided a pro though the reaction proceeds, and may be conducted at, cess for the preparation of difluoromethane which pro temperatures higher than 25 C., for example up to 100 cess comprises contacting dichloromethane or chloro C., in which case the halogenated alkane may be in the fluoromethane with a transition metal fluoride selected vapour phase. The process of the invention is preferably from Osfs, Irfs, ReF6 and RuFs and maintaining the operated under substantially anhydrous conditions, and contact until at least a portion of the dichloromethane is conveniently operated at atmospheric pressure, al or chlorofluoromethane has been converted to di though superatomospheric or subatmospheric pressures fluoromethane. The reaction mixture may, if desired, may be employed, if desired. also contain hydrogen fluoride. The transition metal fluoride may, at the reaction 65 The process of the invention is also of particular temperature, be present in the reaction vessel in the value for the preparation of 1,1,1,2-tetrafluoroethane solid or vapour phase, and may be supported on a sub from 2-chloro-1,1,1-trifluoroethane and accordingly in strate, for example aluminium fluoride or carbon. a further aspect of the invention there is provided a 5,254,772 3 4. process for the preparation of 1,1,1,2-tetrafluoroethane T-piece were evacuated, passivated with R2 and re which comprises contacting 2-chloro-1,1,1-trifluoroe evacuated. thane with a transition metal fluoride selected from 236 mg, 2.78 mmol of CH2Cl2 was sublined into the Osfs, Irf6, and ReF6 and maintaining the contact until FEP tube cooled to -196° C. in liquid nitrogen. The at least a portion of the 2-chloro-1,1,1-trifluoroethane PTFE valve was closed and the reaction mixture al has been converted to 1,1,1,2-tetrafluoroethane. The lowed to warm slowly to -78 C. in a dry-ice-acetone reaction mixture may, if desired, also contain hydrogen bath and then to room temperature (20', C.) with fre fluoride. quent shaking. After 1 hour the solution had turned The process of the invention is also of particular from its original yellow colour to black and there was a value for the preparation of dichlorofluoromethane by 10 black precipitate. The FEP tube and PTFE valve were contacting dichloromethane with ReF7, UF6 or VFs taken off the vacuum line and re-weighed. and of 2-chloro-1,1,1,2-tetrafluoroethane by contacting The FEP reaction tube and a second FEP tube were 2-chloro-1,1,1-trifluoroethane with Rufs, ReF, Crfs, connected to the vacuum line via a PTFE T-piece, and VF5 or UF6 and these processes represent further par the connectors and T-piece were evacuated, passivated ticular embodiments of the invention.