Carbylamine reaction is used as a test for
(A) aromatic primary amine
(B) aliphatic primary amine
(C) aliphatic secondary amine
(D) substituted aromatic secondary amine
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → (A) and (B) only
In the carbylamine reaction (isocyanide test), an amine is heated with chloroform and ethanolic potassium hydroxide. Chloroform and KOH give dichlorocarbene, \( \ce{:CCl2} \), which reacts with the –\( \ce{NH2} \) group; both hydrogen atoms on nitrogen are removed with the two chlorine atoms, and an isocyanide (carbylamine) with a very unpleasant smell is formed. Because the nitrogen must give up two hydrogen atoms, only primary amines, aliphatic or aromatic, give the test:
\( \displaystyle \ce{R-NH2 + CHCl3 + 3KOH} \xrightarrow{\text{heat}} \ce{R-NC + 3KCl + 3H2O} \)
(A) aromatic primary amine — Correct. Aniline gives phenyl isocyanide:
\( \displaystyle \ce{C6H5NH2 + CHCl3 + 3KOH} \xrightarrow{\text{heat}} \ce{C6H5NC + 3KCl + 3H2O} \)
(B) aliphatic primary amine — Correct. Ethylamine, for example, gives ethyl isocyanide, \( \ce{C2H5NC} \), in the same way.
(C) aliphatic secondary amine — Incorrect. A secondary amine, \( \ce{R2NH} \), has only one hydrogen on nitrogen, so it cannot form an isocyanide.
(D) substituted aromatic secondary amine — Incorrect. N-methylaniline, \( \ce{C6H5NHCH3} \), also has only one N–H hydrogen and gives no isocyanide.
NCERT (2026-27 edition):
Carbylamine Reaction
