steam distillation of 4-bromoaniline , why render it basic prior
In principle, it is difficult to distill salts (ionic compounds). Therefore you first make sure that you have a free base in the solution. This is guaranteed in alkaline solution. For the steam distillation the compounds should be immiscible, which is another reason for having a free base. Let’s compare boiling points and solubility for aniline and its salt:


Aniline b.p. 184 °C, solubility in water: 36 g/L
Anilinium chloride b.p. 245 °C, solubility in water: 1070 g/L