What is the major product 'Z' in the given reaction sequence?
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Diazonium salts are extremely versatile intermediates in aromatic chemistry. Key replacement reactions to remember:
- with H\(_3\)PO\(_2\) or CH\(_3\)CH\(_2\)OH: Replaced by -H (deamination).
- with H\(_2\)O/warm: Replaced by -OH (forms phenol).
- with CuCl/HCl (Sandmeyer): Replaced by -Cl.
- with KI: Replaced by -I.
Let's analyze the reaction sequence step by step.
Step 1: Formation of X.
The starting material is nitrobenzene (C\(_6\)H\(_5\)NO\(_2\)). It is treated with Fe/HCl.
This is a standard method for the reduction of a nitro group to a primary amine group.
\( \text{C}_6\text{H}_5\text{NO}_2 + 6[\text{H}] \xrightarrow{\text{Fe/HCl}} \text{C}_6\text{H}_5\text{NH}_2 + 2\text{H}_2\text{O} \).
So, compound X is aniline.
Step 2: Formation of Y.
Aniline (X) is treated with NaNO\(_2\)/HCl at 273 K (0 °C). This is the diazotization reaction.
The primary amine group is converted into a diazonium salt.
\( \text{C}_6\text{H}_5\text{NH}_2 \xrightarrow{\text{NaNO}_2/\text{HCl}} [\text{C}_6\text{H}_5\text{N}_2]^+\text{Cl}^- \).
So, compound Y is benzenediazonium chloride.
Step 3: Formation of Z.
Benzenediazonium chloride (Y) is treated with hypophosphorous acid (H\(_3\)PO\(_2\)) and water.
This is a deamination reaction, where the diazonium group (-\(N_2^+\)) is replaced by a hydrogen atom. It is a reduction reaction.
\( [\text{C}_6\text{H}_5\text{N}_2]^+\text{Cl}^- + \text{H}_3\text{PO}_2 + \text{H}_2\text{O} \rightarrow \text{C}_6\text{H}_6 + \text{N}_2 + \text{H}_3\text{PO}_3 + \text{HCl} \).
The major organic product, Z, is benzene (C\(_6\)H\(_6\)).
