Patent GB-672757-A (GB)
Title: Improvements in and relating to the manufacture of unsaturated organic halides
IPC: C07C17/20
Filed: 1950-01-11
Abstract: Unsaturated organic halides are obtained by heating a mixture comprising an unsaturated organic compound containing at least one allylic halogen atom and an aqueous medium containing a halide of an alkali metal or of an alkaline earth metal carrying a different halogen so as to cause halogen exchange.  An allylic halogen atom is defined as one which is attached to a saturated carbon atom adjacent to an olefinically unsaturated carbon atom.  The term halogen covers chlorine, bromine or iodine and the word "halide" signifies the chloride, bromide or iodide.  The process may be effected by heating up to 200 DEG  C. and is preferably effected at 70-120 DEG  C. at atmospheric pressure.  The organic halide starting materials preferably contain 3 to 10 carbon atoms and those specified are: 1 : 3-dichloro-2-methylpropane, 1 - chloro - 2 - chloromethyl - 2 - propene, 1 - phenyl - 3 - chloro - 1 - propene, a -chloromethylacrylic acid, 3 - chloro - methyl-3 - butenol, a  - bromomethyl crotonaldehyde, 3 - chloro - 1 - decene, 3 - iodo - 1 : 4 - pentadiene, 1 : 2 : 3 - trichloropropene, and the aliphatic mono olefinic dichlorides such as 1,3 - dichloropropene, 1 : 4 - dichloro - 2-butene and b -chloro-methylallyl chloride.  The metal halides are those of lithium, sodium, potassium, rubidium, caesium, magnesium, calcium, strontium and barium.  They may be employed individually or as a mixture of two or more compounds, and are preferably employed in the form of an aqueous solution which is saturated at the reaction temperature.  The mixing of the reactants may be aided by adding a small amount of soap or a non-ionic emulsifying agent such as glyceryl monooleate or the polyethylene oxides and a small amount of a corrosion inhibitor, e.g. an amine nitrite may also be added. About 0.1 to 10 equivalent weights of halogen as metal halide to each mole of organic halide may be employed.  The process can be conducted batchwise or as a continuous or multistage operation and is particularly adapted to recycling operations.  In examples: (1) and (2) 1-chloro-3-bromo-1-propene is obtained by heating under reflux a mixture of 1 : 3-dichloropropene and an aqueous solution of sodium bromide and calcium bromide respectively; (3) a mixture of 1 - bromo - 4 - chloro - 2 - butene and 1 : 4-di-bromo-2-butene is obtained by refluxing a mixture of 1 : 4-dichloro-2-butene and an aqueous solution of sodium bromide; (4) a -bromethylacrylonitrile is obtained from a -chloromethylacrylonitrile and an aqueous solution of sodium bromide; (5) a mixture of chlorobromoisobutenes and b  - bromomethylallylbromide is obtained by refluxing a mixture of 1 : 3 - dichloro - 2 - methylpropene and b -chloromethylallyl chloride with an aqueous solution of sodium bromide; (6) 2-chloro-3-bromo-1-propene is similarly obtained from 2 : 3 - dichloro - 1 - propene and an aqueous solution of sodium bromide; (7) a mixture of organic halides is obtained by refluxing a mixture of the mixed chlorination products of propylene, predominating in 1 : 3-dichloropropene and containing 2 : 3-dichloropropene, 1 : 2-dichloropropane and other organic halides, with an aqueous solution of sodium bromide.  A comparative example is given in which 1 : 3-dichloropropene is treated with anhydrous calcium bromide to yield 1-chloro-3-bromo-1-propene.