JEE Main 2021 · 16 March · evening · Single correct · +4 / −1
Ammonolysis of Alkyl halides followed by the treatment with NaOH solution can be used to prepare primary, secondary and tertiary amines. The purpose of NaOH in the reaction is :
- (a) to remove acidic impurities
- (b) to remove basic impurities
- (c) to activate NH₃ used in the reaction
- (d) to increase the reactivity of alkyl halide
Answer and solution
Answer (a) to remove acidic impurities
Solution
Chemistry ma’am · 4 steps
Ammonolysis gives you the amine as a salt with HX; NaOH is the base that sets the free amine loose.
- What forms first. NH₃ attacks the alkyl halide and gives an amine plus HX. The amine is basic, so it picks up that HX and stays in the mixture as a substituted ammonium salt, RNH₃⁺X⁻.
- The problem. The HX and the ammonium salts are the acidic part of the mixture. As long as the amine is tied up in them, you cannot collect it as a free base.
RNH₃⁺X⁻ + NaOH → RNH₂ + NaX + H₂O
- Role of NaOH. NaOH is a strong base. It neutralises the acid and pulls the proton off the ammonium salt. That leaves the free amine and a harmless salt, NaX.
- So. NaOH is added to remove the acidic impurities (HX and the ammonium salts) and release the free amine. The answer is (a).
The idea to keep. An amine made in the presence of an acid ends up as its ammonium salt. Whenever a strong base is added at the end of an amine preparation, its job is to neutralise that acid and free the amine.
Answer from the NTA final answer key. Solution by PrepWiser.