Read the passage carefully and answer the Questions.
Amines are classified as primary (1°), secondary (2°) and tertiary (3°) depending upon the number of hydrogen atoms replaced by alkyl or aryl groups in ammonia molecules. Aliphatic amines are a stronger bases due to +I effect of an alkyl groups. Intermolecular hydrogen bonding in primary and secondary amines affects the boiling points of amines. The intermolecular association is more in primary amines than in secondary amines as there are more number of hydrogen atoms available for hydrogen bond formation. Nitro compounds are reduced to amines by passing hydrogen gas in the presence of finely divided nickel, palladium or platinum and also by reduction with metals in an acidic medium. Gabriel synthesis is used for the preparation of primary amines. Primary amines react with nitrous acid to give unstable diazonium-salts which can be used to synthesize a variety of compounds.
The product in the following reaction is
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → phenol
A primary aromatic amine reacts with nitrous acid in the cold to give a diazonium salt (diazotisation). Nitrous acid is unstable, so it is made in the mixture itself from sodium nitrite and hydrochloric acid, and the temperature is kept at 273–278 K so that the diazonium salt does not decompose:
\( \displaystyle \ce{C6H5NH2 + NaNO2 + 2HCl} \xrightarrow{\text{273-278 K}} \ce{C6H5N2^+Cl^- + NaCl + 2H2O} \)
When the aqueous solution of benzenediazonium chloride is allowed to warm up (to about 283 K), water replaces the diazonium group, nitrogen gas is given off and phenol is formed:
\( \displaystyle \ce{C6H5N2^+Cl^- + H2O} \xrightarrow{\text{warm}} \ce{C6H5OH + N2 ^ + HCl} \)
So the product with nitrous acid, HCl and water is phenol.
Why the other options are incorrect
Option (1) toluene — Incorrect. No reagent here supplies a methyl group; the diazonium group is replaced by OH from water.
Option (2) chlorobenzene — Incorrect. Chlorobenzene needs copper(I) chloride in HCl (Sandmeyer reaction): \( \ce{C6H5N2^+Cl^-} \xrightarrow{\ce{Cu2Cl2/HCl}} \ce{C6H5Cl + N2} \). Without the copper salt, water gives phenol.
Option (4) N-phenylhydroxylamine — Incorrect. It is a partial reduction product of nitrobenzene (for example with zinc and ammonium chloride), not a product of diazotisation.
NCERT (2026-27 edition):
Replacement by Hydroxyl Group
