Step 1: Diazotisation of aniline.
Aniline reacts with sodium nitrite and hydrochloric acid at \(273\) K to form benzene diazonium chloride.
\[
C_6H_5NH_2
\rightarrow
C_6H_5N_2^+Cl^-
\]
Step 2: Hydrolysis of diazonium salt.
On warming with water,
\[
C_6H_5N_2^+Cl^-
\rightarrow
C_6H_5OH
\]
Phenol is produced.
Step 3: Reimer-Tiemann reaction.
Phenol reacts with chloroform and aqueous sodium hydroxide.
The formyl group is introduced mainly at the ortho position.
\[
C_6H_5OH
\xrightarrow[NaOH]{CHCl_3}
o\text{-Hydroxybenzaldehyde}
\]
Step 4: Identify the product.
\(o\)-Hydroxybenzaldehyde is commonly called salicylaldehyde.
\[
{\text{Salicylaldehyde}}
\]
