JEE Main · 2024 · 29 Jan 2024 · Shift 2 · Compounds Containing Nitrogen

Treating a primary aromatic amine with $\mathrm{NaN}{\mathrm{O}}_2/HCl$ at 0${}^{\circ }$C generates the aryldiazonium chloride, $\mathrm{Ar}-{\mathrm{N}}_2^{+}\mathrm{C}{\mathrm{l}}^{-}$, through nitrosation of the amine followed by loss of water.

Reacting this diazonium salt with cuprous chloride ($\mathrm{C}{\mathrm{u}}_2\mathrm{C}{\mathrm{l}}_2$) is a Sandmeyer reaction: the diazonium group is displaced by chlorine through a radical pathway mediated by the Cu(I)/Cu(II) couple, regenerating the aromatic ring with $-\mathrm{Cl}$ at the position that previously carried $-{\mathrm{N}}_2^{+}$, leaving the rest of the ring unchanged.

The product A is the aryl chloride formed by direct Sandmeyer substitution of the diazonium group with chlorine.