Which product is formed on carbylamine reaction with 4-methylaniline?
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Carbylamine reaction is a special test for primary amines only. The product always contains the isocyanide group \( \mathrm{-NC} \), not the nitrile group \( \mathrm{-CN} \).
Step 1: Recall the carbylamine reaction.
The carbylamine reaction is shown by primary amines only. In this reaction, a primary amine reacts with chloroform and alcoholic potassium hydroxide to form an isocyanide or carbylamine. The general reaction is:
\[
\mathrm{RNH_2 + CHCl_3 + 3KOH \rightarrow RNC + 3KCl + 3H_2O}
\]
Step 2: Identify the given amine.
4-methylaniline is a primary aromatic amine. Its structure is \( p\text{-}\mathrm{CH_3C_6H_4NH_2} \). Since it is a primary amine, it gives the carbylamine test. Step 3: Determine the product formed.
In the carbylamine reaction, the amino group \( \mathrm{-NH_2} \) is converted into the isocyanide group \( \mathrm{-NC} \). Therefore, 4-methylaniline forms 4-methylphenyl isocyanide, whose formula is:
\[
p\text{-}\mathrm{CH_3C_6H_4NC}
\]
This corresponds to option (B). Step 4: Compare with the other options.
(A) \( p\text{-}\mathrm{CH_3C_6H_4CN} \): This is a nitrile, not the product of carbylamine reaction.
(B) \( p\text{-}\mathrm{CH_3C_6H_4NC} \): Correct. This is the isocyanide formed in the carbylamine reaction.
(C) \( p\text{-}\mathrm{CH_3C_6H_4NO_2} \): This is a nitro compound, not related to the carbylamine reaction.
(D) \( p\text{-}\mathrm{CH_3C_6H_4N_2^+Cl^-} \): This is a diazonium salt, formed in diazotisation, not in carbylamine reaction.
Step 5: Conclusion.
Hence, the product formed in the carbylamine reaction of 4-methylaniline is \( p\text{-}\mathrm{CH_3C_6H_4NC} \). Final Answer:\( p\text{-}\mathrm{CH_3C_6H_4NC} \).
