Which of the following will form tri-bromo derivative of phenol ?

Options

A.
B.
C.
D.

Answer

To determine which of the given compounds will form a tri-bromo derivative of phenol, we need to analyze the effects of substituents on the phenol ring and how they influence electrophilic aromatic substitution reactions.

### Step-by-Step Solution:

1. **Identify the Substituents on Phenol**:
- We have phenol as our base compound. The substituents can either be activating or deactivating groups, and they can also be ortho/para-directing or meta-directing.

2. **Analyze the First Option**:
- The first option has a methyl group (–CH₃) attached to phenol. Both the –OH (hydroxyl) and –CH₃ groups are ortho/para-directing and activating groups.
- However, the ortho position of the methyl group blocks the para position of the hydroxyl group, making it impossible for bromine to substitute at the para position.
- Therefore, this option will not lead to a tri-bromo derivative.

3. **Analyze the Second Option**:
- The second option also has a methyl group on the ortho position relative to the hydroxyl group.
- Similar to the first option, the ortho position of the methyl group blocks the para position of the hydroxyl group, preventing substitution at both ortho and para positions.
- Thus, this option will also not form a tri-bromo derivative.

4. **Analyze the Third Option**:
- The third option involves phenol reacting with Br₂ in a non-polar solvent (CS₂).
- In this case, phenol can yield mono-bromo derivatives (ortho and para) but not tri-bromo derivatives, as the solvent does not ionize phenol to form phenoxide ions.

5. **Analyze the Fourth Option**:
- The fourth option involves phenol reacting with Br₂ in an aqueous solution.
- In this scenario, phenol ionizes to form phenoxide ions, which significantly increases the electron density on the ring, allowing for multiple substitutions.
- The presence of water as a solvent leads to the formation of a tri-bromo derivative (246-tribromophenol) due to the enhanced reactivity of the phenoxide ion.

### Conclusion:
The compound that will form a tri-bromo derivative of phenol is the one reacting in an aqueous solution, leading to the formation of phenoxide ions, which activate the ring for multiple substitutions.