The preparation of 4-bromoacetanilide from acetanilide and bromine involves electrophilic aromatic substitution EAS reaction, while the preparation of aniline from nitrobenzene involves a reduction reaction. Here are the mechanisms for both reactions:1. Preparation of 4-bromoacetanilide from acetanilide and bromine:Step 1: Formation of the electrophileBromine Br2 reacts with a Lewis acid catalyst, such as aluminum bromide AlBr3 or iron III bromide FeBr3 , to form the electrophile, bromonium ion Br+ .Br2 + AlBr3/FeBr3 Br+ + AlBr4-/FeBr4-Step 2: Electrophilic attack on the aromatic ringThe electrophile, Br+, attacks the aromatic ring of acetanilide, which is activated by the electron-donating amino group -NHCOCH3 at the para position. This leads to the formation of a sigma complex, with a positive charge on the carbon atom.Step 3: Deprotonation and regeneration of the catalystA base, usually the halide ion Br- formed in step 1, abstracts a proton from the sigma complex, resulting in the formation of 4-bromoacetanilide and regenerating the Lewis acid catalyst.2. Preparation of aniline from nitrobenzene:The conversion of nitrobenzene to aniline involves a reduction reaction, which can be carried out using various reducing agents, such as hydrogen gas H2 in the presence of a metal catalyst e.g., palladium on carbon , or using tin Sn and hydrochloric acid HCl .Step 1: Reduction of the nitro groupThe nitro group -NO2 in nitrobenzene is reduced to an intermediate hydroxylamine derivative -NHOH by the reducing agent.Step 2: Further reduction and protonationThe hydroxylamine derivative is further reduced to form an amine group -NH2 , which then gets protonated to form aniline.In summary, the preparation of 4-bromoacetanilide from acetanilide and bromine involves an electrophilic aromatic substitution reaction, while the preparation of aniline from nitrobenzene involves a reduction reaction. These two mechanisms are fundamentally different in terms of the type of reaction and the intermediates involved.