Question

Primary amines ${\text{(RN}}{{\text{H}}_{\text{2}}}{\text{)}}$ reacts with nitrous acid to give:
A. ${\text{RNH}}_3^ + {\text{N}}{{\text{O}}_{\text{2}}}$
B.${\text{ROH}}$
C. ${\text{ROR}}$
D.none of these

Answer 1

Hint: We should know how nitrous acid and amine behaves. The nitrous acid gives ${\text{N}}{{\text{O}}^{\text{ + }}}$ cation. The nitrogen of amine works as a nucleophile. The primary amine can both hydrogen and nitrogen as nitrogen gas to give an alkyl cation. Alkyl can be treated with water.

Complete Answer :
The amines are basic due to the presence of lone pairs on nitrogen, so behave as a nucleophile. Nitric acid generates electrophile ${\text{N}}{{\text{O}}^{\text{ + }}}$. The nucleophilic amine attacks on electrophile ${\text{N}}{{\text{O}}^{\text{ + }}}$ so, the nitrogen of amine gets positive change thus loses one proton. Then, the second proton from the nitrogen of amine transfers to the oxygen of electrophile ${\text{N}}{{\text{O}}^{\text{ + }}}$ forming a nitrogen-nitrogen double bond ${\text{R}}\, - \,{\text{N = N}}\, - \,{\text{OH}}$. Then –OH abstract protons and lose water molecules to form ${\text{R}}\, - \,{\text{N}}_2^ + $. Nitrogen gas removed to give alkyl cation.

The product of the reaction of a primary amine ${\text{(RN}}{{\text{H}}_{\text{2}}}{\text{)}}$ with nitrous acid is shown as follows:
${\text{RN}}{{\text{H}}_{\text{2}}}\,{\text{ + HN}}{{\text{O}}_{\text{2}}}\, \to \,{\text{ROH}}\,\, + \,{{\text{N}}_2}\, + \,{{\text{H}}_{\text{2}}}{\text{O}}$

The reaction of primary amine ${\text{(RN}}{{\text{H}}_{\text{2}}}{\text{)}}$ with nitrous acid gives primary alcohol, water and nitrogen gas. Nitrogen is colourless and odourless gas. By the evolution of the gas, primary amines are identified.
So, primary amines ${\text{(RN}}{{\text{H}}_{\text{2}}}{\text{)}}$ reacts with nitrous acid to give alcohol ${\text{ROH}}$.

Therefore, option (B) ${\text{ROH}}$, is correct.

Note: The different amines react differently with nitrous acid. Primary amines form alcohol. Secondary amines form nitroso compounds. The secondary amine gives N-alkyl-N-nitroso alkylamine and water. The N-alkyl-N-nitroso alkylamine is yellow coloured oil. So, secondary amines are identified by the formation of a yellow oil. The tertiary amine does not react. This reaction is used for distinguished primary, secondary and tertiary amine compounds.