Reaction Bromination of an Aromatic Compound

Example Mono- and Di-brombenzene from Bromine and Benzene 

The by-prodtict, hydrobromic acid, is purified as described in the Inorganic Part. (See page 345-) 

In most cases, however, the principal product may be separated from the by-product without difficulty by distillation or crystallisation. Since the hydrogen atoms substituted by bromine combine with bromine to form hydrobromic acid, therefore, for the introduction of each bromine atom, a molecule (two atoms of bromine) must be used. 

The introduction of bromine can be essentially facilitated by the use of a so-called bromine carrier. As such, the bromides of metalloids, or metals, are used (1) either in the already prepared condition, or (2) they can be generated from their elements in the reaction. To the first class belong ferric bromide and aluminium bromide. The action of ferric bromide depends on the fact that on being reduced to ferrous bromide, it yields bromine in statu nascendi  

Since the ferrous bromide unites with bromine again, to form ferric bromide, a small quantity of this has the power to transfer an indefinitely large quantity of bromine  

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