Answer the question on the basis of passage given below:
There are three kinds of amines which are primary, secondary and tertiary amines. These amines may have alkyl group or aryl group or both alkyl and aryl groups. These amines can be distinguished from one another by various chemical tests.
An amine \(A\) on treatment with \(HNO_2\) gives \(N_2\) (g) and an alcohol \(B\). The molecular mass of alcohol \(B\) is \(46\). The amine \(A\) is:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → CH3CH2NH2
Primary, secondary and tertiary amines react differently with nitrous acid (made in situ from \( \ce{NaNO2} \) and HCl). Primary aliphatic amines form aliphatic diazonium salts, which are unstable and decompose at once, liberating nitrogen gas and giving an alcohol:
\( \ce{RNH2 + HNO2} \xrightarrow{\ce{NaNO2 + HCl}} \ce{[RN2^+Cl^-]} \xrightarrow{\ce{H2O}} \ce{ROH + N2 ^ + HCl} \)
An alcohol of molecular mass 46 is ethanol, \( \ce{C2H5OH} \) (2 × 12 + 6 × 1 + 16 = 46). The alcohol keeps the alkyl group of the amine, so A is ethylamine:
\( \ce{CH3CH2NH2 + HNO2 -> CH3CH2OH + N2 ^ + H2O} \)
Why the other options are incorrect
Option (1) CH3NH2 — Incorrect. A primary amine that gives \( \ce{N2} \), but the alcohol is methanol, \( \ce{CH3OH} \) (molecular mass 32).
Option (3) CH3NHCH3 — Incorrect. A secondary amine; with nitrous acid it gives a yellow oily N-nitrosamine, \( \ce{(CH3)2N-N=O} \), and no \( \ce{N2} \).
Option (4) (CH3)3N — Incorrect. A tertiary amine; it only forms a soluble nitrite salt, with no \( \ce{N2} \) and no alcohol.
NCERT (2026-27 edition):
Chemical Reactions – …
