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 `H2SO4` at high temperature, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Reactants**:
- The reactant is phenol (C6H5OH) and it is being reacted with sulfuric acid (H2SO4).

2. **Understand the Nature of Phenol**:
- Phenol is an activated aromatic compound. The hydroxyl group (-OH) is an electron-donating group, which increases the electron density on the benzene ring. This makes the ring more reactive towards electrophilic substitution reactions.

3. **Electrophilic Substitution Reaction**:
- When phenol reacts with sulfuric acid, the electrophile generated is the sulfonium ion (SO3H+). The reaction is an electrophilic aromatic substitution where the electrophile (SO3H) will attach to the benzene ring.

4. **Determine the Positions for Electrophilic Attack**:
- Due to the resonance structures of phenol, the electron density is increased at the ortho and para positions of the benzene ring. Therefore, the electrophile can attack either the ortho or para position, but not the meta position.

5. **Consider the Reaction Conditions**:
- The reaction is conducted at high temperatures. At elevated temperatures, steric hindrance and stability of the product become significant factors. The ortho product (ortho phenol sulfonic acid) experiences steric repulsion due to the bulky SO3H group being close to the -OH group.

6. **Identify the Major Product**:
- Although both ortho and para phenol sulfonic acids can be formed, the para product is more stable due to less steric hindrance. Therefore, at high temperatures, the major product will be para phenol sulfonic acid.

7. **Conclusion**:
- The main product formed when phenol reacts with `H2SO4` at high temperature is para phenol sulfonic acid.

### Final Answer:
The main product is **para phenol sulfonic acid**.

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