b. Explain why a much better yield of primary amine is obtained from the reaction of an alkyl halide with azide ion
(-N3), followed by catalytic hydrogenation. (Hint: An alkyl azide is not nucleophilic.)


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Verified step by step guidance

1. Identify the reaction sequence: The reaction involves two main steps - the nucleophilic substitution of an alkyl halide with azide ion ($-N_3$) to form an alkyl azide, followed by catalytic hydrogenation to produce a primary amine.
2. Understand the role of azide ion: The azide ion ($-N_3$) is a good nucleophile that can effectively displace the halide ion in an alkyl halide through an $S_{N}2$ mechanism, forming an alkyl azide.
3. Recognize the stability of alkyl azides: Alkyl azides are stable intermediates and do not undergo further reactions easily because they are not nucleophilic, preventing side reactions that could reduce yield.
4. Consider the hydrogenation step: Catalytic hydrogenation of the alkyl azide reduces it to a primary amine. This step is selective and efficient, leading to high yields of the desired amine product.
5. Compare with other methods: Other methods of synthesizing primary amines from alkyl halides often involve competing side reactions or over-alkylation, which can lower the yield of the primary amine. The azide route avoids these issues, providing a cleaner and more efficient pathway.

Key Concepts

Nucleophilicity

Nucleophilicity refers to the ability of a species to donate an electron pair to form a chemical bond. In this context, azide ion (-N3) acts as a nucleophile, attacking the alkyl halide to form an alkyl azide. However, alkyl azides are not nucleophilic due to the resonance stabilization of the azide group, which makes them less reactive in further nucleophilic reactions.

Catalytic Hydrogenation

Catalytic hydrogenation is a chemical reaction that involves the addition of hydrogen (H2) to a compound in the presence of a catalyst, typically a metal such as palladium or platinum. In this case, after the formation of the alkyl azide, catalytic hydrogenation reduces the azide group to a primary amine, effectively converting the non-nucleophilic azide into a more reactive amine, thus improving the yield.

Reaction Mechanism

Understanding the reaction mechanism is crucial for predicting the outcome of chemical reactions. In this scenario, the mechanism involves the nucleophilic substitution of the alkyl halide by the azide ion, followed by the reduction of the azide to a primary amine. This stepwise approach allows for a more efficient transformation, leading to a higher yield of the desired product compared to direct reactions involving less stable intermediates.