GB730690A - Process for the production of pure anhydrous crystalline alkali metal bromides - Google Patents

Abstract

<PICT:0730690/III/1> Pure anhydrous finely crystalline alkali metal bromides are produced by a process wherein an anhydrous alkyl bromide, especially methyl bromide, is reacted at a temperature maintained below 50 DEG C. throughout the reaction with an anhydrous alkali metal hydroxide in an anhydrous liquid which has a substantially lower solvent power for the alkali metal bromide formed than for the corresponding alkali metal hydroxide. It is preferred to use the alkali metal bromide as a liquid but reaction in the vapour state may be arranged to take place in a column in countercurrent flow to the liquid containing alkali metal hydroxide. Suitable solvents are aliphatic alcohols, ethanol, propanol and butanol being referred to, but methanol is preferred. The process may be carried out continuously, e.g. in a flow tube or column, and the liquid in the reaction product may be recirculated to the reaction after making up with alkali metal hydroxide. In the example, sodium hydroxide was stirred into methyl alcohol, and methyl bromide added little by little with cooling. The temperature first rose to 42 DEG C., and was kept until the end of the reaction at 20-25 DEG C. The sodium bromide was filtered off after two hours and had a purity of 99.5 per cent. In the apparatus shown, anhydrous medium is mixed with solid alkali metal hydroxide in vessel 13 provided with a stirrer and the solution passed into reaction vessel 1. This also contains a stirrer to mix the solution with alkyl bromide entering through pipe 7. The condenser 6 returns condensed vapours to the reaction vessel. Alkali metal bromide is precipitated and falls into conical section 2 from which it can be withdrawn through valve 3 into a sieve centrifuge 9 where it is separated from the liquid, which is returned, together with the anhydrous medium from pipe 18, used as washing liquid, to the reaction vessel. The process may be worked particularly advantageously in combination with the production of alkyl bromides, e.g. as described in Specification 730,682, [Group IV (b)].