The correct sequence of reagents used in the preparation of 4-bromo-2-nitroethyl benzene from benzene is :

Options

A. `HNO_3//H_2SO_4, Br_2//AlCl_3. CH_3COCl//AlCl_3, Zn-Hg//HCl`
B. `Br_2//AlBr_3, CH_3COCl//AlCl_3, HNO_3//H_2SO_4, Zn//HCl`
C. `CH_3COCl//AlCl_3, Br_2//AlBr_3, HNO_3//H_2SO_4 , Zn//HCl`
D. `CH_3COCl//AlCl_3, Zn-Hg//HCl, Br_2//AlBr_3, HNO_3//H_2SO_4`

Answer

To synthesize 4-bromo-2-nitroethyl benzene from benzene, we need to follow a specific sequence of reactions. Here’s a step-by-step breakdown of the process:

### Step 1: Alkylation of Benzene
- **Reagent**: Ethyl bromide (C2H5Br) and a Lewis acid catalyst (FeBr3).
- **Reaction**: Benzene reacts with ethyl bromide in the presence of FeBr3 to undergo Friedel-Crafts alkylation. This introduces an ethyl group (C2H5) onto the benzene ring.
- **Product**: Ethyl benzene (C6H5C2H5).

### Step 2: Bromination of Ethyl Benzene
- **Reagent**: Bromine (Br2) and a Lewis acid catalyst (FeBr3).
- **Reaction**: Ethyl benzene is treated with bromine in the presence of FeBr3. The ethyl group is an ortho/para-directing group, so bromination occurs predominantly at the para position due to steric hindrance at the ortho position.
- **Product**: 4-bromoethyl benzene (C6H4BrC2H5).

### Step 3: Nitration of 4-Bromoethyl Benzene
- **Reagents**: A nitrating mixture of concentrated nitric acid (HNO3) and concentrated sulfuric acid (H2SO4).
- **Reaction**: The 4-bromoethyl benzene undergoes nitration. The ethyl group directs the incoming nitro group (NO2) to the ortho and para positions, but since the para position is blocked by the bromine, the nitro group will attach at the ortho position.
- **Product**: 2-nitro-4-bromoethyl benzene (C6H4BrC2H4NO2).

### Final Product:
The final compound is 4-bromo-2-nitroethyl benzene.

### Summary of the Sequence:
1. **Alkylation**: Benzene + C2H5Br + FeBr3 → Ethyl benzene
2. **Bromination**: Ethyl benzene + Br2 + FeBr3 → 4-bromoethyl benzene
3. **Nitration**: 4-bromoethyl benzene + HNO3 + H2SO4 → 4-bromo-2-nitroethyl benzene

### Correct Sequence of Reagents:
1. C2H5Br (ethyl bromide) + FeBr3
2. Br2 + FeBr3
3. HNO3 + H2SO4