CBSE 2025, Set 2

Question

Why is the ammonolysis of alkyl halides not considered a good method to prepare pure primary amines?

Edvaya · Accepted Answer

The correct answer is Subjective. When an alkyl halide (RX) reacts with ammonia ($	ext{NH}_3$), the primary amine ($	ext{RNH}_2$) that is initially formed is more nucleophilic and basic than ammonia itself. As a result, the primary amine competes with ammonia to react with the remaining alkyl halide. This leads to a continuous chain of nucleophilic substitution reactions: $$	ext{RX} + 	ext{NH}_3 ightarrow 	ext{RNH}_2 \xrightarrow{	ext{RX}} 	ext{R}_2	ext{NH} \xrightarrow{	ext{RX}} 	ext{R}_3	ext{N} \xrightarrow{	ext{RX}} 	ext{R}_4	ext{N}^+	ext{X}^-$$ The final product is an inseparable **mixture of primary, secondary, and tertiary amines, along with a quaternary ammonium salt**. Because separating this complex mixture into pure components is highly difficult, ammonolysis is not a good method for synthesizing a single, pure primary amine.

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Chemistry > Organic Chemistry > Amines

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