Question

Identify the compounds which can react with chloroform and alcoholic KOH and give substances with offensive odour (Carbylamine test).

• A. I, II only
• B. II, III only
• C. II, IV only
• D. I, III only

Hint:

Only primary amines ($1^\circ$) react with $CHCl_3$ and alc. KOH to produce foul-smelling isocyanides.

Answer 1

The Correct Option is C

Step 1: Recall the carbylamine test.
The carbylamine test uses chloroform and alcoholic KOH. It gives isocyanides, which have a very bad, offensive smell.

Step 2: Know which amines respond.
Only primary amines ($R-NH_2$), which have an $-NH_2$ group with two hydrogens on nitrogen, give a positive carbylamine test. Secondary and tertiary amines do not.

Step 3: Check the tertiary amine.
N,N-Dimethylaniline is a tertiary amine, so it has no $N-H$ hydrogens to react. It gives a negative test.

Step 4: Check the secondary amine.
N-Methyl-o-methylaniline is a secondary amine, so it also fails the test and is negative.

Step 5: Find the primary amines.
2,4-Dimethylaniline and p-Methylbenzylamine both carry a free $-NH_2$ group, so they are primary amines and give a positive carbylamine test with the offensive odour. These match II and IV.

Step 6: State the answer.
So the compounds that respond are II and IV.
\[ \boxed{\text{II, IV only}} \]