The preparation of 4-bromoacetanilide from acetanilide and bromine involves an electrophilic aromatic substitution reaction. Here is a detailed step-by-step process with energy changes and intermediate formation:1. Generation of electrophile:Bromine Br2 reacts with a Lewis acid catalyst, such as aluminum bromide AlBr3 or iron III bromide FeBr3 , to form a highly electrophilic bromonium ion Br+ . This step is endothermic as energy is required to break the Br-Br bond and form the electrophile.Br2 + AlBr3 Br+ + AlBr4-2. Formation of sigma complex arenium ion :The electrophilic bromonium ion Br+ attacks the aromatic ring of acetanilide at the para position due to the activating effect of the amino group to form a sigma complex, also known as an arenium ion. This step is also endothermic as energy is required to break the aromaticity of the ring and form a new bond between the carbon and the electrophile.Acetanilide + Br+ para-Arenium ion sigma complex 3. Rearrangement and deprotonation:A proton from the carbon adjacent to the newly attached bromine atom is removed by the AlBr4- ion or another base , which acts as a base. This step is exothermic as energy is released when the aromaticity of the ring is restored and a new C-Br bond is formed.para-Arenium ion sigma complex + AlBr4- 4-bromoacetanilide + HAlBr4Overall, the reaction is an electrophilic aromatic substitution, and the energy changes involve endothermic steps for electrophile generation and sigma complex formation, followed by an exothermic step for deprotonation and product formation. The intermediate formed during the reaction is the para-arenium ion sigma complex .