Question

Give the diazotization reaction of aniline. Also, give the chemical reaction involved in the preparation of red azo dye and light yellow azo dye.

Answer 1

Hint: The conversion of a primary amine into its diazonium salt is called diazotization. The temperature required for this reaction is in the range of 273K to 278K.

Complete step by step answer: Aromatic diazonium salt is generally prepared by adding a cold aqueous solution of sodium nitrite to the solution or suspension of a primary aromatic amine in acid at 273K to 278K. The general reaction is written as:
$ArN{H}_2+NaN{O}_2+2HX\stackrel{273K-278K}{\to }Ar{N}_2^{+}{X}^{-}+NaX+2H_{2}O$
Where Ar is an aryl group and X is halogen.
In the case of aniline diazotization reaction is written as:

Arenediazonium salts react with a highly reactive aromatic compound such as phenol and amines to form brightly colored azo compounds. This reaction is known as a coupling reaction.
The chemical reaction involved in the preparation of red azo dye:

In this reaction, diazonium salt reacts with β-Naphthol in the presence of dil. NaOH at PH 9-10, i.e. in alkali medium to give β-Naphthol aniline dye, i.e. red azo dye.
The chemical reaction involved in the formation of yellow dye:

In this reaction, diazonium salt reacts with aniline in the presence of dil. NaOH at PH 4-5, i.e. in acidic medium to give p-Aminoazobenzene, i.e. yellow dye.

Note: The well-known indicator methyl orange used in acid-base titration is also prepared by a coupling reaction. So we can say diazonium salts are very good intermediates.