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Explanation of the Correct Answer
In the ammonolysis of alkyl halides, alkyl halides (R–X) react with ammonia (NH3) to eventually form primary, secondary, or tertiary amines. However, during the course of this reaction, acidic byproducts (such as HX or ammonium salts) may be generated. These acidic species need to be removed or neutralized in order to obtain the desired amines effectively.
1. Ammonolysis of Alkyl Halides
The general ammonolysis reaction can be represented as:
$ \text{R–X} + \text{NH}_3 \longrightarrow \text{R–NH}_2 + \text{HX} $
Depending on conditions and further reaction steps, the initially formed primary amine (R–NH2) can further react to form secondary (R2NH) or tertiary (R3N) amines. During these substitutions, acidic byproducts, generally HX, are produced.
2. Role of NaOH in the Reaction
After the main ammonolysis step, the reaction mixture often contains acidic impurities such as HX or protonated amine salts (for instance, R–NH3+ X−). Treating the mixture with NaOH serves to remove or neutralize these acidic components:
$ \text{HX} + \text{NaOH} \longrightarrow \text{NaX} + \text{H}_2\text{O} $
By scavenging these acidic species, NaOH ensures that the amines remain in their free-base form (i.e., R–NH2, R2NH, or R3N), improving the overall yield and purity of the amines.
3. Conclusion
Thus, the primary purpose of adding NaOH in this process is to neutralize or remove the acidic impurities formed (such as HX) and to free the amines from their protonated forms, thereby giving a good yield of the desired amines.
