Ethylamine (C$$_2$$H$$_5$$NH$$_2$$) can be obtained from N-ethylphthalimide on treatment with:

The Core Concept: Gabriel Phthalimide Synthesis

This question refers to a classic step in the Gabriel Phthalimide Synthesis, a premier method used to prepare pure primary aliphatic amines (like ethylamine) without the risk of over-alkylation.

The process generally follows three main stages:

1. Deprotonation: Phthalimide is treated with KOH to form potassium phthalimide.
2. Alkylation: The potassium phthalimide reacts with an alkyl halide (in this case, ethyl halide) via an $\text{S}_\text{N}2$ mechanism to yield N-ethylphthalimide.
3. Cleavage (Hydrazinolysis): The primary amine is liberated from the phthalimide core.

Why Hydrazine

Traditionally, the cleavage of the N-alkylphthalimide can be achieved via harsh acidic or basic hydrolysis ($\text{H}_2\text{O}$ / $\text{H}^+$ or $\text{OH}^-$), but this process is often slow and requires brutal reaction conditions.

To make things cleaner and much faster, Ing and Manske introduced the use of hydrazine, a process known as hydrazinolysis.

The Reaction:

When N-ethylphthalimide is treated with hydrazine, a nucleophilic acyl substitution takes place:

• Product 1: Ethylamine — The desired primary amine.
• Product 2: Phthalhydrazide — A highly stable, insoluble cyclic byproduct that easily precipitates out, making the isolation of your pure amine incredibly simple.

Why the Other Options Don't Work

• A) CaH2 (Calcium Hydride): This is a strong, non-nucleophilic reducing agent/drying agent. It will not cleave the imide ring to yield a primary amine.
• C) H2): Plain water at room temperature will not react with N-ethylphthalimide. It requires strong acids/bases and prolonged heating to force hydrolysis.
• D) NaBH4 (Sodium Borohydride): This is a mild reducing agent that generally reduces aldehydes and ketones. It is not strong enough to cleanly cleave the phthalimide ring down to the primary amine in this standard synthetic pathway.