-NH2 is a powerful activating, o/p directing group (+M > -I). Problem: aniline is SO activated that direct reactions give polysubstitution and/or oxidation. Bromination: C6H5NH2 + 3Br2(aq) -> 2,4,6-tribromoaniline (white ppt, no catalyst). Controlled bromination: (1) Acetylate: C6H5NH2 + (CH3CO)2O -> C6H5NHCOCH3. (2) Brominate: -> p-BrC6H4NHCOCH3 (acetamido group is moderately activating, gives mono para). (3) Hydrolyse: -> p-BrC6H4NH2. Nitration problem: Conc. HNO3/H2SO4 oxidises the -NH2 group. Solution: (1) Protect as acetamide. (2) Nitrate (gives mainly para). (3) Deprotect. Alternative: Use dilute HNO3 at low temperature for o/p-nitroaniline mixture without protection.