Patent GB-695315-A (GB)
Title: Improvements in or relating to the production of organic bromides
Inventor: LAKE DOUGLAS EDWARD
IPC: C07C17/20
Filed: 1951-03-05
Abstract: A chlorine-containing organic compound which contains a chlorine atom attached to a carbon atom in the aliphatic or alicyclic portion of the molecule, which is free of functional groups other than halogen atoms and carbonyl, carboxy, alkoxy and acyl halide groups, which remains at least 95 per cent unpolymerized when admixed with 5 mol. per cent of aluminium chloride at 0-90 DEG  C. for 1 hour, which does not undergo dehydrohalogenation to form a more readily polymerizable unsaturated organic compound under the above conditions and which contains chlorine directly attached to a carbon atom of its molecule is formed into a liquid mixture with hydrogen bromide and contacted with a chloride or bromide of aluminium or boron at temperatures below that at which the brominated compound, obtained by replacement of the chlorine atom of the chlorine-containing organic compound with bromine, is decomposed.  The metal chloride or bromide is usually used in proportions of 2-5 mol. per cent of total reactants. Aluminium chloride and bromide and boron trichloride and tribromide are specified.  The metal chloride or bromide may be formed in situ by reacting other compounds of the metals, e.g. aluminium hydroxide, acetate or sulphate or metallic aluminium, with the hydrogen bromide and any water which may also be formed is removed to below 0.1 per cent of free water by the use of a dehydrating agent.  Many chlorine-containing organic compounds are specified, representative being carbon tetrachloride, methyl chloride, dichlorodibromomethane, methylene chloro-bromide, butyl chloride, ethylene chlorobromide, benzyl chloride, chloroacetic acid, ethyl-chloromethyl ketone, cyclohexyl chloride, chloromethyl methyl ether, propionyl chloride and alphachloro-acetyl bromide.  The reaction is advantageously effected at temperatures below the atmospheric boiling-point of the chlorine-containing reactant and temperatures of 0-150 DEG  or 200 DEG  C. are mentioned.  Atmospheric pressure is usually used.  The product may correspond with the starting compound but isomers are sometimes formed, e.g. isobutyl chloride yields tertiary butyl bromide and normal butyl chloride yields secondary butyl bromide and generally secondary or tertiary bromides are obtained. Polychloro compounds may be substituted with bromine to any desired degree.  The process may be made continuous by passing the reactants through a bed of the metal chloride or bromide. Diluents, e.g. ethyl or propyl bromide, may be present.  In examples, hydrogen bromide is reacted in the presence of aluminium chloride with (1) and (2) carbon tetrachloride to give carbon tetrabromide, tribromo-chloro-methane, dibromodichloromethane and monobromo - trichloromethane; (4) chloroform to give dichloro-monobromo- and dibromo-monochloro-methane; (8) sec.-butyl, n-butyl, tert.-butyl and isobutyl chlorides and trimethylene-chloro-bromide, n-dodecyl chloride and monochloroacetic acid to give sec.-butyl bromide, n-butyl and sec.-butyl bromides, tert.-butyl bromide, tert.-butyl and a minor amount of isobutyl bromide, trimethylene bromide together with 1,2-propylene bromide and propylene-chloro-bromides, a dodecyl bromide and monobromoacetic acid respectively; (9) acetyl chloride to yield acetyl bromide; and (10) cyclohexylchloride to yield cyclohexyl bromide, in the presence of aluminium bromide with (3) and (5) chloroform to yield dichloromonobromo- and dibromo-monochloro-methane and bromoform respectively; and (7) methylene chloride to yield methylene bromide and methylene chlorobromide; in the presence of boron bromide in (11) with carbon tetrachloride to give monobromo-trichloro-, monobromo-dichloro- and tribromo-monochloro-methane and in the presence of aluminium powder in (6) with chloroform to yield monobromo-dichloro- and dibromo-mono-chloromethane.