Phenol on reaction with `H_2SO_4` at high temperature gives mainly

Options

A. o - phenol sulfonic acid
B. para - phenol sulfonic acid
C. meta - phenol sulfonic acid
D. none of these

Answer

To solve the question regarding the reaction of phenol with concentrated sulfuric acid (H₂SO₄) at high temperature, we can follow these steps:

### Step 1: Understand the Reactants
Phenol (C₆H₅OH) is an aromatic compound with a hydroxyl (-OH) group attached to a benzene ring. Concentrated sulfuric acid (H₂SO₄) is a strong acid that can act as a sulfonating agent.

**Hint:** Identify the structure of phenol and the properties of concentrated sulfuric acid.

### Step 2: Reaction Conditions
The question specifies that the reaction occurs at high temperature. The temperature at which the reaction occurs can influence the product formed. At high temperatures, the sulfonation of phenol tends to favor the formation of para-substituted products.

**Hint:** Recall how temperature affects the regioselectivity of electrophilic aromatic substitution reactions.

### Step 3: Identify the Product
When phenol reacts with concentrated H₂SO₄ at high temperatures, the main product formed is para-phenol sulfonic acid (C₆H₄(SO₃H)(OH)), also known as para-hydroxybenzenesulfonic acid. This occurs because the para position is less hindered compared to the ortho position, allowing for easier electrophilic attack.

**Hint:** Consider the stability and steric effects of the possible products (ortho vs. para).

### Step 4: Eliminate Incorrect Options
- **Ortho-phenol sulfonic acid** is formed at lower temperatures, so this option is incorrect.
- **Meta-phenol sulfonic acid** is not a major product of this reaction, so this option is also incorrect.
- **None of these** is not applicable since we have identified a correct product.

**Hint:** Review the characteristics of the products formed under different conditions to eliminate options.

### Conclusion
Based on the analysis, the correct answer to the question is that phenol reacts with concentrated sulfuric acid at high temperature to primarily yield **para-phenol sulfonic acid**.

**Final Answer:** Para-phenol sulfonic acid.