Animated Solution for Chemistry - Organic Chemistry: Ethylamine (${\text{C}}_2{\text{H}}_5{\text{NH}}_2$) can be obtained from N-ethylphthalimide on treatment with

The Final Act

Imagine you are a molecular architect, and your goal is to build a pristine, primary amine without any messy secondary or tertiary amine byproducts. This is exactly what the Gabriel phthalimide synthesis achieves! The problem we are tackling focuses on the grand finale of this synthesis: the release of the primary amine from its protective phthalimide cage.

We start with N-ethylphthalimide. Think of the phthalimide group as a robust, bulky protective shield. It has done its job perfectly by preventing the nitrogen atom from reacting more than once with an alkyl halide. But now, we need to remove this shield to get our desired product: ethylamine (${\text{C}}_2{\text{H}}_5{\text{NH}}_2$).

To break the strong carbon-nitrogen bonds of the imide, we need a chemical tool that is sharp and aggressive. We need a powerful nucleophile.

Hydrazine

Enter hydrazine (${\text{NH}}_2{\text{NH}}_2$). Why is hydrazine such a fantastic choice here? It all comes down to the alpha-effect. Hydrazine has two adjacent nitrogen atoms, both possessing lone pairs of electrons. These lone pairs repel each other slightly, raising the energy of the molecule and making it an exceptionally eager and powerful nucleophile.

When we heat N-ethylphthalimide with hydrazine, a nucleophilic acyl substitution takes place. The hydrazine attacks the highly electrophilic carbonyl carbons of the phthalimide ring. It acts like a pair of molecular scissors, systematically snipping the two $\text{C}-\text{N}$ bonds.

As the bonds break, the ethylamine is finally set free! But what happens to the phthalimide shield? It doesn't just fall apart into a messy soup. Instead, it reacts with the hydrazine to form a highly stable, 6-membered cyclic compound known as phthalhydrazide.

This is the thermodynamic genius of the reaction. The formation of this incredibly stable byproduct acts as a massive driving force, pushing the reaction to completion and ensuring a high yield of our pure primary amine.

While concentrated aqueous alkali (like $\text{NaOH}$ or $\text{KOH}$) can also be used to hydrolyze the imide, the hydrazine method (often called the Ing-Manske procedure) is frequently preferred in the laboratory because it is cleaner and highly efficient.