Benzene diazonium chloride on reaction with phenol in a basic medium gives:

Options

A. Diphenyl ether
B. p-Hydroxyazobenzene
C. Chlorobenzene
D. Benzene

Answer

To solve the question regarding the reaction of benzene diazonium chloride with phenol in a basic medium, we can follow these steps:

### Step 1: Identify the Reactants
The reactants in this reaction are benzene diazonium chloride (C6H5N2Cl) and phenol (C6H5OH). Benzene diazonium chloride contains a diazonium group (N2+) which is highly reactive.

**Hint:** Look for the functional groups in the reactants; the diazonium group is key to the reaction.

### Step 2: Understand the Reaction Conditions
The reaction takes place in a basic medium. The presence of a base will deprotonate phenol, making it a better nucleophile due to the increased electron density on the aromatic ring.

**Hint:** Remember that basic conditions enhance nucleophilicity by removing protons from phenol.

### Step 3: Mechanism of the Reaction
1. The hydroxyl group (–OH) on phenol donates its lone pair of electrons to the benzene diazonium ion, leading to the formation of a new bond between the phenol and the diazonium ion.
2. The nitrogen in the diazonium group (N2+) is positively charged and will be attacked by the electron-rich aromatic ring of phenol.
3. This results in the formation of an intermediate where the diazonium group is now bonded to the aromatic ring, and a chloride ion (Cl-) is released.

**Hint:** Focus on how the electron donation from the hydroxyl group stabilizes the transition state.

### Step 4: Regeneration of Aromaticity
To regain aromaticity, the intermediate undergoes a rearrangement:
1. A proton (H+) from the hydroxyl group is abstracted by the base, leading to the formation of a double bond between the nitrogen and the aromatic ring.
2. This results in the formation of para-hydroxyazobenzene (C6H5N=NH-C6H4OH).

**Hint:** Aromaticity is crucial; the reaction mechanism often involves steps to restore it.

### Step 5: Final Products
The final products of the reaction are para-hydroxyazobenzene (C6H4(OH)-N=N-C6H5), along with the by-products HCl and water.

**Hint:** Always check for the by-products formed during the reaction.

### Conclusion
Thus, the correct answer to the question is that benzene diazonium chloride reacts with phenol in a basic medium to give **para-hydroxyazobenzene**.

**Final Answer:** Para-hydroxyazobenzene