A compound \(C_3H_5N\) undergoes reduction to form a primary amine. The amine gives compounds [B] and [C] in the following reactions. Identify [B] and [C].
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Only primary amines give the carbylamine test and produce foul-smelling isocyanides. Nitriles on reduction always form primary amines having one extra carbon atom in the chain.
Understanding the Concept:
This question is based on the chemistry of nitriles and primary amines. Nitriles undergo reduction to produce primary amines. Primary amines further undergo several characteristic reactions such as:
Carbylamine reaction giving isocyanides
Acylation reactions producing amides
Only primary amines respond positively to the carbylamine test, which is an important identification reaction in organic chemistry.
Step 1: Identification of the compound \(C_3H_5N\).
The molecular formula given is:
\[
C_3H_5N
\]
A compound having this molecular formula and capable of producing a primary amine on reduction is a nitrile.
Hence the compound is:
\[
\mathrm{CH_3CH_2CN}
\]
which is known as propanenitrile or ethyl cyanide.
The structure can be written as:
\[
\mathrm{CH_3-CH_2-C \equiv N}
\]
The presence of the nitrile group:
\[
\mathrm{-C \equiv N}
\]
is responsible for its reduction to a primary amine.
Step 2: Reduction of nitrile to primary amine.
Nitriles undergo catalytic hydrogenation in the presence of nickel catalyst or can also be reduced using reducing agents such as:
\[
\mathrm{LiAlH_4}
\]
During reduction, the triple bond between carbon and nitrogen gets converted into a single bond and the nitrile carbon becomes attached to:
\[
\mathrm{-CH_2NH_2}
\]
Thus:
\[
\mathrm{CH_3CH_2CN
\xrightarrow{H_2/Ni}
CH_3CH_2CH_2NH_2}
\]
The product formed is:
\[
\mathrm{CH_3CH_2CH_2NH_2}
\]
which is propylamine.
Propylamine is a primary amine because the amino group:
\[
\mathrm{-NH_2}
\]
is attached to only one alkyl group.
Step 3: Formation of isocyanide by carbylamine reaction.
Primary amines undergo the carbylamine reaction when heated with chloroform and alcoholic potassium hydroxide.
The general reaction is:
\[
\mathrm{RNH_2 + CHCl_3 + 3KOH
\rightarrow
RNC + 3KCl + 3H_2O}
\]
In this reaction:
\(RNH_2\) is a primary amine
\(RNC\) is an isocyanide or carbylamine
Since propylamine is a primary amine, it gives this reaction successfully.
Hence compound [C] is:
\[
[C] = \text{isocyanide}
\]
This reaction is extremely important because secondary and tertiary amines do not give the carbylamine test.
Step 4: Formation of amide from primary amine.
Primary amines react with acid chlorides such as acetyl chloride to produce amides.
The reaction is:
\[
\mathrm{RNH_2 + CH_3COCl
\rightarrow
RNHCOCH_3 + HCl}
\]
In this process:
The hydrogen atom of the amino group gets replaced
An acyl group gets attached to nitrogen
An amide linkage is formed
Therefore the product [B] formed is an amide.
Hence:
\[
[B] = \text{amide}
\]
Step 5: Final conclusion.
From the above reactions:
\[
[B] = \text{amide}
\]
and
\[
[C] = \text{isocyanide}
\]
Therefore the correct option is:
\[
\boxed{(3)}
\]
