PhMgBr (Grignard reagent ) cannot be used to prepare the compound ?

Options

A.
B.
C.
D.

Answer

To determine which compound cannot be prepared using phenyl magnesium bromide (Grignard reagent), we will analyze the four options provided.

### Step-by-Step Solution:

1. **Understanding Grignard Reagents**: Grignard reagents, such as phenyl magnesium bromide (PhMgBr), are powerful nucleophiles that can react with electrophiles to form new carbon-carbon bonds. They can react with carbonyl compounds, esters, and other electrophilic species.

2. **Option A: Benzoic Acid**
- **Reaction**: PhMgBr can react with carbon dioxide (CO2) to form benzoic acid. The reaction proceeds as follows:
- PhMgBr + CO2 → PhCOOMgBr (Grignard adduct)
- Hydrolysis of the adduct yields benzoic acid (PhCOOH).
- **Conclusion**: Benzoic acid can be synthesized using PhMgBr.

3. **Option B: 2-Phenyl Ethanol**
- **Reaction**: PhMgBr can react with an epoxide (oxirane) to open the ring and form 2-phenyl ethanol:
- PhMgBr + Epoxide → Grignard adduct
- Hydrolysis of the adduct yields 2-phenyl ethanol.
- **Conclusion**: 2-Phenyl ethanol can be synthesized using PhMgBr.

4. **Option C: Acetophenone**
- **Reaction**: PhMgBr can react with acetyl chloride (CH3COCl) to form acetophenone:
- PhMgBr + CH3COCl → Grignard adduct
- Hydrolysis of the adduct yields acetophenone (PhCOCH3).
- **Conclusion**: Acetophenone can be synthesized using PhMgBr.

5. **Option D: Tertiary Butyl Benzene**
- **Reasoning**: Tertiary butyl benzene (t-BuPh) cannot be synthesized using PhMgBr because:
- Tertiary butyl groups (t-Bu) are not electrophilic enough to react with the nucleophilic Grignard reagent.
- The reaction would require a stable carbocation, which is not feasible in this case.
- **Conclusion**: Tertiary butyl benzene cannot be synthesized using PhMgBr.

### Final Answer:
The compound that cannot be prepared using phenyl magnesium bromide (Grignard reagent) is **Tertiary Butyl Benzene** (Option D).

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