Question

$3$Ammonolysis of alkyl halides followed by the treatment with $\mathrm{NaOH}$ solution can be used to prepare primary, secondary and tertiary amines. The purpose of $\mathrm{NaOH}$ in the reaction is:

• A. to remove basic impurities
• B. to activate ${\mathrm{NH}}_3$ in the reaction
• C. To increase the reactivity of alkyl halide
• D. to remove acidic impurities

Answer 1

The correct option is D

to remove acidic impurities

Explanation for correct option:

(D) to remove acidic impurities

The ammonolysis of alkyl halide takes place in the following steps:

Step 1: $$\begin{gathered} \mathrm{RX}+{\mathrm{NH}}_3\to \mathrm{R}-\mathrm{NH}+\mathrm{NaX}+{\mathrm{H}}_2\mathrm{O} \\ \mathrm{Alkyl}\mathrm{halide}1°\mathrm{amine} \end{gathered}$$

Step 2 : $$\begin{gathered} \mathrm{R}-\mathrm{NH}+\mathrm{RX}+\mathrm{NaOH}\to \mathrm{R}-\mathrm{NH}-\mathrm{R}+\mathrm{NaX}+{\mathrm{H}}_2\mathrm{O} \\ 1°\mathrm{amine}2°\mathrm{amine} \end{gathered}$$

Step 3 : $\mathrm{R}-\mathrm{NH}-\mathrm{R}+\mathrm{RX}+\mathrm{NaOH}\to {\mathrm{R}}_3\mathrm{N}+\mathrm{NaX}+{\mathrm{H}}_2\mathrm{O}$

From step 3 it can be observed that that the acidic impurities $\left(\mathrm{RX}\right)$ formed in the reaction is removed by $\mathrm{NaOH}$ forming $\mathrm{NaX}$ as by-product.

Explanation of incorrect options:

(A) to remove basic impurities

No basic impurities are formed in the process, this can be observed from the reactions above

(B) to activate ${\mathbf{NH}}_{\mathbf{3}}$ in the reaction

It can be observed from the above reactions that no activation of ${\mathrm{NH}}_3$ is required in the reaction.

(C) to increase the reactivity of alkyl halide

$\mathrm{NaOH}$ do not show catalytic type of activity in this type of reaction.

Hence, option D is correct, The purpose of $\mathrm{NaOH}$ in the reaction is to remove basic impurities.