Reaction CLXIV.—Replacement of Hydrogen by Nascent Halogen

Reaction CLXIV. Replacement of Hydrogen by Nascent Halogen.— 

An excess of bromate and sulphuric acid is often employed to react with the hydrobromic acid formed during the bromination of the substance. 

Nascent chlorine or iodine can be generated from their corresponding salts in a similar manner. For the use of standard bromate in estimations, see p. 500. 

35 gms. of p-nitroaniline are dissolved in 312 c.cs. cone, hydrochloric acid at 50°. A solution of 20-5 gms. of potassium chlorate in 437 c.cs. of water at about 25° are slowly added. When all the chlorate has been added the solution is diluted with a large quantity of water the precipitate formed is removed by filtration and well washed. It can be further purified by crystallisation from glacial acid or from a mixture of glacial acetic acid and alcohol. 

30 gms. (3 mols.) of stearic acid and 1-1 gms. (1 atom) of red phosphorus are placed in a flask fitted with a reflux condenser and dropping funnel. The flask is immersed in a water bath containing water at 60°—70°, so that the stearic acid melts, and 22-5 gms. (4 mols.) of dry bromine are added gradually from the dropping funnel. When addition is complete the mixture is heated on a boiling water bath for about 3 hours. The product is poured into water, and the monobromostearic acid filtered off and dried on a porous plate. It is recrystallised from carbon disulphide. 

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