(ii) From amines by Sandmeyer’s reaction
When a primary aromatic amine, dissolved or suspended in cold
aqueous mineral acid, is treated with sodium nitrite, a diazonium
salt is formed Mixing the solution of freshly prepared diazonium
salt with cuprous chloride or cuprous bromide results in the
replacement of the diazonium group by –Cl or –Br Replacement of the diazonium group by iodine does not require the
presence of cuprous halide and is done simply by shaking the diazonium
salt with potassium iodide 6