Which of the following amine (s) show (s) positive carbylamine test?
B. (CH₃)₂NH
C. CH₃NH₂
D. (CH₃)₃ N
Choose the correct answer from the options given below:

Solution

Chemistry ma’am · 3 steps

Look at the nitrogen, not the ring: only an -NH₂ group with two H atoms on N gives an isocyanide.

1. The test. An amine is warmed with chloroform and alcoholic KOH. A primary amine turns into an isocyanide (carbylamine), which has a very foul smell.

   R-NH₂ + CHCl₃ + 3KOH → R-NC + 3KCl + 3H₂O

2. Why only primary. The carbon in R-N≡C is joined to nitrogen by a triple bond. To form it, the nitrogen must give up both of its H atoms. Secondary amines have only one H on N and tertiary amines have none, so they cannot react. Primary amines react whether R is alkyl or aryl.

   Amine	H atoms on N	Type	Carbylamine test
   A: aniline, C₆H₅NH₂	2	primary (aromatic)	positive
   B: (CH₃)₂NH	1	secondary	negative
   C: CH₃NH₂	2	primary (aliphatic)	positive
   D: (CH₃)₃N	0	tertiary	negative
   E: N-methylaniline, C₆H₅NHCH₃	1	secondary	negative

3. So. Only the two primary amines, aniline (A) and methylamine (C), give the foul-smelling isocyanide. The answer is (d).

The idea to keep. Carbylamine test is the primary-amine test. Count the H atoms on nitrogen: two means positive, whether the group is alkyl or aryl. One or zero means negative.

Answer from the NTA final answer key. Solution by PrepWiser.