Which of the following reactions can be used to introduce bromine atom in benzene ring ?

Options

A.
B.
C.
D.

Answer

To determine which reactions can introduce a bromine atom into a benzene ring, we will analyze each reaction step by step.

### Step 1: Analyze the First Reaction
- **Reaction**: Benzene + BrCl (in the presence of FeCl3)
- **Mechanism**: This is an electrophilic aromatic substitution reaction. The FeCl3 acts as a catalyst and helps generate the electrophile (Br+). The Br+ then attacks the benzene ring, substituting a hydrogen atom for a bromine atom.
- **Product**: A brominated benzene ring is formed.

**Conclusion**: This reaction can introduce a bromine atom into the benzene ring. **(Correct)**

### Step 2: Analyze the Second Reaction
- **Reaction**: Benzene + Br (in the presence of sodium ethoxide, NaOEt)
- **Mechanism**: Initially, bromine adds to the benzene ring, but then the sodium ethoxide facilitates a dehydrohalogenation reaction. This means that instead of forming a brominated benzene, the reaction results in the formation of benzene without the bromine.
- **Product**: No brominated product is formed; only benzene is obtained.

**Conclusion**: This reaction does not introduce a bromine atom into the benzene ring. **(Incorrect)**

### Step 3: Analyze the Third Reaction
- **Reaction**: N2Cl + CuBr
- **Mechanism**: This is known as the Sandmeyer reaction. The N2Cl can generate a bromine electrophile which can then substitute a hydrogen atom on the benzene ring.
- **Product**: A brominated benzene ring is formed.

**Conclusion**: This reaction can introduce a bromine atom into the benzene ring. **(Correct)**

### Step 4: Analyze the Fourth Reaction
- **Reaction**: Benzene + HOBR
- **Mechanism**: This is another electrophilic substitution reaction. The HOBR can provide the Br+ electrophile, which will substitute a hydrogen atom on the benzene ring.
- **Product**: A brominated benzene ring is formed.

**Conclusion**: This reaction can introduce a bromine atom into the benzene ring. **(Correct)**

### Final Conclusion
The reactions that can introduce a bromine atom into the benzene ring are:
1. Benzene + BrCl (in the presence of FeCl3)
3. N2Cl + CuBr (Sandmeyer reaction)
4. Benzene + HOBR

Thus, the correct options are 1, 3, and 4.

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