Aniline is treated with $(\mathrm{CH}{}_3\mathrm{CO}){}_2\mathrm{O}$, then with $\mathrm{Br}{}_2$ in ethanoic acid, and the product is hydrolysed with aqueous acid. The major final organic product is:

Acetylation lowers the activating power of nitrogen because its lone pair is shared with the carbonyl. Bromination of acetanilide therefore stops at monosubstitution, mainly at the para position. Hydrolysis then gives 4-bromoaniline. Direct bromination of aniline would give the tribromo compound.