Patent GB-390191-A (GB)
Title: Improvements in process of producing carbon halides
IPC: C07C17/20
Filed: 1931-06-29
Abstract: Fluorinated paraffin hydrocarbons are prepared by reacting a halogenated paraffin hydrocarbon containing a halogen other than fluorine with an alkali or alkaline earth metal fluoride. Chloro- and bromoderivatives of paraffin hydrocarbons are especially suitable as starting materials, mention being made of carbon tetrachloride, chloroform, hexachlorethane and tetrachlorethane.  The reaction is especially concerned with the replacement of halogen by fluorine, but replacement of hydrogen may occur, particularly if a free halogen such as chlorine is present in the reaction mass.  Sodium and calcium fluorides are suitable fluorinating agents.  Calcium fluoride may be employed either as precipitated calcium fluoride or natural fluorspar, and should be brought into a fine state of subdivision before being formed into pills or otherwise agglomerated for use, a small addition of calcium chloride being useful as a binder.  The reaction may be carried out by passing vapours of carbon tetrachloride through a vessel containing the heated fluoride, the reaction temperature lying between 350 DEG  C. and the fusion point of the solid fluoride-chloride mixture formed by the reaction, for example, between 350 DEG  and 550 DEG  C.  The vapours from the reaction vessel are passed through a water-cooled or refrigerated condenser, which returns unreacted carbon tetrachloride to the vaporizer while allowing the fluorinated compounds, mostly consisting of defluorodichloromethane and fluorotrichloromethane, to pass on. These gaseous products are purified by scrubbing and then liquefied by low temperature condensation or by compression and water cooling. It is desirable, in order to minimize side reactions, to use starting materials free from impurities, and particularly free from water. The process may be carried out at super-atmospheric or sub-atmospheric pressure.  The use of apparatus resistant to corrosion is not essential.  The gaseous products may be fractionated immediately after their formation.  Examples are given.  The Specification as open to inspection under Sect. 91 comprises also the fluorination of any acyclic halogenated hydrocarbon, including olefines and the like in addition to paraffins, and also aryl derivatives of chain compounds such as benzotrichloride.  It also comprises the use of any metal fluoride as a fluorinating agent, mention being made of light and heavy metal fluorides including fluorides of lead, bismuth, and zinc, or metals of Groups I, II, IV, and VIII, of the Periodic table, particularly metals having specific gravities between seven and fourteen.  The use of catalysts and the admixture with the reaction mass of antimony salts, which may or may not act as catalysts, is also included.  Pentavalent antimony salts such as antimony pentachloride or pentabromide may function as catalysts per se, or a trivalent antimony salt such as antimony sulphate or antimony trichloride is used, a catalyst such as chlorine or antimony pentachloride may be employed in conjunction.  When heavy metal fluorides are used as fluorinating agents, the reaction may be effected at temperatures approximating to the refluxing temperature of the carbon tetrachloride or of the reaction mass containing it. The provision of suitable means for removing the chlorides formed from the reaction zone is referred to.  When unsaturated acyclic compounds are fluorinated, the introduction of fluorine and the addition of halogen may take place in the same operation, particularly when free halogen is present.  The process may be improved by incorporating ammonium chloride with the reaction mass, for example when calcium fluoride is used as the fluorinating agent. Examples of the fluorination of carbon tetrachloride using the additional fluorinating agents referred to above are included.  This subject-matter does not appear in the Specification as accepted.