Which gas will be evolved out when primary amine is treated with sodium nitrite and HCI ?

Options

A. Chlorine
B. Ammonia
C. Nitrogen
D. `NO_2`

Answer

To solve the question of which gas is evolved when a primary amine is treated with sodium nitrite (NaNO2) and hydrochloric acid (HCl), we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Reactants**:
- Sodium nitrite (NaNO2) is a source of nitrous acid (HNO2) when it reacts with hydrochloric acid (HCl).
- The reaction can be represented as:
\[ \text{NaNO}_2 + \text{HCl} \rightarrow \text{HNO}_2 + \text{NaCl} \]

2. **Formation of Nitrous Acid**:
- Nitrous acid (HNO2) is unstable and can react with primary amines (R-NH2) to form diazonium salts.
- The reaction can be represented as:
\[ \text{R-NH}_2 + \text{HNO}_2 \rightarrow \text{R-N}_2^+ + \text{H}_2\text{O} \]
- Here, R-NH2 is the primary amine.

3. **Formation of Diazonium Ion**:
- The primary amine reacts with nitrous acid to form a diazonium ion (R-N2^+), which is unstable.
- The reaction can be simplified to:
\[ \text{R-N}_2^+ + \text{H}_2\text{O} \rightarrow \text{R-N}_2 + \text{H}_2\text{O} \]
- This shows that water is produced, and the diazonium ion can decompose.

4. **Decomposition of Diazonium Ion**:
- The diazonium ion (R-N2^+) is unstable and can lose nitrogen gas (N2) upon decomposition.
- The overall reaction leads to the evolution of nitrogen gas:
\[ \text{R-N}_2^+ \rightarrow \text{R} + \text{N}_2(g) \]

5. **Conclusion**:
- The gas evolved during this reaction is nitrogen gas (N2).

### Final Answer:
The gas evolved when a primary amine is treated with sodium nitrite and HCl is nitrogen gas (N2).

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