Which of the following reactions are suitable method for the preparation of primary amines?

Options

A. Action of ammonia on alkyl halides
B. Hofmann bromide reaction
C. Gabriel's phthalimide synthesis of amines
D. Hydrogenation of isocyanides

Answer

To determine which reactions are suitable for the preparation of primary amines, we will analyze each option provided in the question.

### Step-by-Step Solution:

1. **Action of Ammonia on Alkyl Halides**:
- When ammonia (NH₃) reacts with an alkyl halide (R-X), it initially forms a primary amine (R-NH₂). However, if the alkyl halide is present in excess, the primary amine can further react with the alkyl halide to form secondary amines (R₂NH) and eventually tertiary amines (R₃N) and quaternary ammonium salts (R₄N⁺).
- **Conclusion**: This method is not suitable for the preparation of primary amines because it leads to multiple products, including secondary and tertiary amines.

2. **Hofmann Bromamide Reaction**:
- In this reaction, a primary amide (R-C(=O)-NH₂) reacts with bromine (Br₂) and potassium hydroxide (KOH) to produce a primary amine (R-NH₂). This reaction specifically yields primary amines and does not lead to the formation of secondary or tertiary amines.
- **Conclusion**: This method is suitable for the preparation of primary amines.

3. **Gabriel Phthalimide Synthesis**:
- In this reaction, phthalimide reacts with a base (like KOH) to form a phthalimide salt, which then reacts with an alkyl halide (R-X) to yield a primary amine after hydrolysis. The reaction specifically produces primary amines without forming secondary or tertiary amines.
- **Conclusion**: This method is suitable for the preparation of primary amines.

4. **Hydrogenation of Isocyanides**:
- When isocyanides (R-N≡C) are subjected to hydrogenation in the presence of acidic water, they yield secondary amines (R-NH-CH₃) rather than primary amines.
- **Conclusion**: This method is not suitable for the preparation of primary amines.

### Final Answer:
The suitable methods for the preparation of primary amines are:
- **B. Hofmann Bromamide Reaction**
- **C. Gabriel Phthalimide Synthesis**