Question

Which of the following reactions will not give a primary amine?

• A. \( \text{CH}_3\text{CONH}_2 \xrightarrow{\text{Br}_2/\text{KOH}} \)
• B. \( \text{CH}_3\text{CN} \xrightarrow{\text{LiAlH}_4} \)
• C. \( \text{CH}_3\text{NC} \xrightarrow{\text{LiAlH}_4} \)
• D. \( \text{CH}_3\text{CONH}_2 \xrightarrow{\text{LiAlH}_4} \)

Hint:

When reducing amides, nitriles, or using the Hofmann Bromamide reaction, primary amines are obtained. However, the reduction of isocyanides produces a secondary amine instead.

Answer 1

The Correct Option is C

The reactions and their respective products are as follows:
(a) Hofmann Bromamide Reaction: \[ \text{CH}_3\text{CONH}_2 \xrightarrow{\text{Br}_2/\text{KOH}} \text{CH}_3\text{NH}_2. \] This reaction involves the conversion of an amide (\( \text{CONH}_2 \)) to a primary amine (\( \text{CH}_3\text{NH}_2 \)) with the loss of one carbon atom.
(b) Reduction of Nitriles: \[ \text{CH}_3\text{CN} \xrightarrow{\text{LiAlH}_4} \text{CH}_3\text{CH}_2\text{NH}_2. \] Nitriles (\( \text{CN} \)) are reduced to primary amines (\( \text{CH}_3\text{CH}_2\text{NH}_2 \)) using lithium aluminium hydride (\( \text{LiAlH}_4 \)).
(c) Reduction of Isocyanides (Methyl Isocyanide): \[ \text{CH}_3\text{NC} \xrightarrow{\text{LiAlH}_4} \text{CH}_3\text{NHCH}_3. \] Isocyanides (\( \text{NC} \)) are reduced to secondary amines (\( \text{CH}_3\text{NHCH}_3 \)) using lithium aluminium hydride. Hence, this reaction does not produce a primary amine.
(d) Reduction of Amides: \[ \text{CH}_3\text{CONH}_2 \xrightarrow{\text{LiAlH}_4} \text{CH}_3\text{CH}_2\text{NH}_2. \] Amides (\( \text{CONH}_2 \)) are reduced to primary amines (\( \text{CH}_3\text{CH}_2\text{NH}_2 \)) using lithium aluminium hydride. Conclusion: Among the given reactions, option (3) does not produce a primary amine; it produces a secondary amine instead. Final Answer: \[ \boxed{\text{CH}_3\text{NC} \xrightarrow{\text{LiAlH}_4} \text{CH}_3\text{NHCH}_3 \text{ (Secondary Amine)}}. \]