Covert fromAniline to 3,5-dibromo-4-iodonitrobenzene

To convert aniline to 3,5-dibromo-4-iodonitrobenzene, we need to follow a series of chemical reactions that introduce the required functional groups at specific positions on the benzene ring. Below is the step-by-step process:

### Step 1: Protection of the Amino Group
Aniline (-NH₂) is a strong activating group, and direct bromination or iodination would lead to undesired multiple substitutions. To control the reactivity, we first convert aniline into acetanilide by acetylation.

**Reaction:**
Aniline reacts with acetic anhydride (CH₃CO)₂O in the presence of pyridine to form acetanilide. This protects the amine group by converting it into an amide (-NHCOCH₃), reducing its activating effect.

**Equation:**
C₆H₅NH₂ + (CH₃CO)₂O → C₆H₅NHCOCH₃ + CH₃COOH

### Step 2: Bromination
Now, we introduce bromine atoms at the 3 and 5 positions. The acetamido (-NHCOCH₃) group is an ortho-para directing group, so bromination will predominantly occur at these positions.

**Reaction:**
Acetanilide reacts with bromine (Br₂) in the presence of glacial acetic acid.

**Equation:**
C₆H₅NHCOCH₃ + 2Br₂ → 3,5-Dibromoacetanilide

### Step 3: Nitration
Next, we introduce a nitro (-NO₂) group at the para position relative to the acetamido group.

**Reaction:**
3,5-Dibromoacetanilide is treated with concentrated nitric acid (HNO₃) and concentrated sulfuric acid (H₂SO₄), leading to nitration at the para position.

**Equation:**
C₆H₃Br₂NHCOCH₃ + HNO₃ → 3,5-Dibromo-4-nitroacetanilide

### Step 4: Hydrolysis of Acetamide to Amine
Now, we remove the protecting acetyl (-COCH₃) group to regenerate the amine (-NH₂).

**Reaction:**
3,5-Dibromo-4-nitroacetanilide is hydrolyzed using dilute hydrochloric acid (HCl) or sodium hydroxide (NaOH), yielding 3,5-dibromo-4-nitroaniline.

**Equation:**
C₆H₃Br₂NHCOCH₃ + H₂O → C₆H₃Br₂NH₂ + CH₃COOH

### Step 5: Sandmeyer Reaction (Diazotization and Iodination)
To introduce iodine at the para position, we first convert the -NH₂ group into a diazonium salt (-N₂⁺) using sodium nitrite (NaNO₂) and hydrochloric acid (HCl), followed by iodination with potassium iodide (KI).

**Reaction:**
3,5-Dibromo-4-nitroaniline reacts with NaNO₂ and HCl at 0-5°C to form 3,5-dibromo-4-nitrobenzenediazonium chloride. This is then treated with KI to introduce iodine at the 4-position.

**Equation:**
C₆H₃Br₂NH₂ + NaNO₂ + HCl → C₆H₃Br₂N₂⁺Cl⁻
C₆H₃Br₂N₂⁺Cl⁻ + KI → C₆H₃Br₂I(NO₂)

### Final Product: 3,5-Dibromo-4-iodonitrobenzene

Thus, through these five steps (protection, bromination, nitration, deprotection, and diazotization-iodination), we successfully convert aniline to 3,5-dibromo-4-iodonitrobenzene.