Question

Carbylamine test is used to detect the presence of primary amino group in an organic compound. Which of the following compound is formed when this test is performed with aniline ?

• A. Phenylmethylamine (NHCH$_3$)
• B. Phenyl cyanide (CN)
• C. Phenyl isocyanide (NC)
• D. Benzamide (CONH$_2$)

Hint:

The key to the carbylamine test is the formation of an isocyanide (-NC) from a primary amine (-NH₂). Secondary and tertiary amines do not give this test. Remember the characteristic foul smell of the isocyanide product.

Answer 1

The Correct Option is C

The carbylamine test, also known as Hoffmann's isocyanide test, is a chemical test for the detection of primary amines.
In this reaction, the primary amine is heated with chloroform (CHCl$_3$) and an alcoholic solution of a strong base, typically potassium hydroxide (KOH).
Aniline (C$_6$H$_5$NH$_2$) is a primary aromatic amine.
When aniline is subjected to the carbylamine test, it reacts to form phenyl isocyanide (also known as phenyl carbylamine).
The reaction is as follows:
C$_6$H$_5$NH$_2$ + CHCl$_3$ + 3KOH $\xrightarrow{\Delta}$ C$_6$H$_5$NC + 3KCl + 3H$_2$O
(Aniline) \hspace{1cm} (Chloroform) \hspace{1.5cm} (Phenyl isocyanide)
Isocyanides are characterized by their extremely unpleasant, foul smell. This pungent odor is the positive indication for the test.
The product formed is phenyl isocyanide, which has the structure C$_6$H$_5$-N$\equiv$C. This matches option (C).