JEE Main 2025 Jan 22 Shift 1, Chemistry Q18: Preparation of Alkyl Halides (Halo Alkanes) & Aryl Halides (Halo Arenes)

Step (i): Bromination of nitrobenzene in AcOH. The $-$NO${}_2$ group is meta-directing and strongly deactivating; under these conditions the major product is the dibromo derivative with Br ortho/para to where future activation will direct, in this scheme giving 2,6-dibromonitrobenzene (Br ortho to the eventual $-$NH${}_2$).

Step (ii): Sn/HCl reduces $-$NO${}_2$ to $-$NH${}_2$, giving 2,6-dibromoaniline.

Step (iii): NaNO${}_2$/HCl at 273 K diazotises the aniline, yielding the 2,6-dibromobenzenediazonium chloride.

Step (iv): Ethanol acts as a hydride source for the reductive deamination of arenediazonium salts. The $-$N${}_2^{+}$ group is replaced by $-$H, while ethanol is oxidised to acetaldehyde (CH${}_3$CHO).

$\therefore$ Products are 1,3-dibromobenzene (the dibromo-arene, A) along with CH${}_3$CHO (B).