How is phenylhydrazine prepared from aniline?

Explanation

To prepare phenylhydrazine from aniline, follow these steps:

### Step 1: Formation of Diazonium Salt
1. **Start with Aniline (PhNH2)**: Aniline is the primary amine that we will use as our starting material.
2. **React with Nitrous Acid (HNO2)**: Treat aniline with nitrous acid, which can be generated in situ by mixing sodium nitrite (NaNO2) with hydrochloric acid (HCl). This reaction leads to the formation of a diazonium salt.
\[ \text{PhNH}_2 + \text{HNO}_2 \rightarrow \text{PhN}_2^+ \text{Cl}^- + \text{H}_2\text{O} \]
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