What is Z in the following reaction sequence?
`C_6H_5NH_2 overset((i) NaNO_2+HCl//273K,(ii) H_3PO_2+H_2O ,(iii) CO ,HCl "anhy".AlCl_3//CuCl)toZ`.

Options

A. `C_(6)H_(5)CO_(2)H`
B. `C_(6)H_(5)OH`
C. `C_(6)H_(5)CHO`
D. `C_(6)H_(6)`

Answer

To determine what Z is in the given reaction sequence, we will analyze each step of the reaction involving aniline (C6H5NH2).

### Step 1: Diazotization of Aniline
1. **Starting Compound**: Aniline (C6H5NH2).
2. **Reagents**: Sodium nitrite (NaNO2) and hydrochloric acid (HCl) at 273 K.
3. **Reaction**: Aniline reacts with NaNO2 and HCl to form benzene diazonium chloride (C6H5N2Cl).
- **Equation**:
\[ C_6H_5NH_2 + NaNO_2 + HCl \rightarrow C_6H_5N_2Cl + NaCl + 2H_2O \]
4. **Product**: Benzene diazonium chloride (C6H5N2Cl).

### Step 2: Reduction of Diazonium Salt
1. **Starting Compound**: Benzene diazonium chloride (C6H5N2Cl).
2. **Reagents**: Hypophosphorous acid (H3PO2) and water.
3. **Reaction**: The diazonium group (N2Cl) is removed, resulting in the formation of benzene (C6H6).
- **Equation**:
\[ C_6H_5N_2Cl + H_3PO_2 + H_2O \rightarrow C_6H_6 + HCl + H_3PO_3 \]
4. **Product**: Benzene (C6H6).

### Step 3: Formation of Benzaldehyde
1. **Starting Compound**: Benzene (C6H6).
2. **Reagents**: Carbon monoxide (CO), hydrochloric acid (HCl), anhydrous aluminum chloride (AlCl3), and copper(I) chloride (CuCl).
3. **Reaction**: Benzene reacts with CO and HCl in the presence of AlCl3 and CuCl to form benzaldehyde (C6H5CHO).
- **Equation**:
\[ C_6H_6 + CO + HCl \xrightarrow{AlCl_3, CuCl} C_6H_5CHO \]
4. **Product**: Benzaldehyde (C6H5CHO).

### Final Result
Thus, the final product Z in the reaction sequence is **benzaldehyde (C6H5CHO)**.

### Summary of Steps
1. Aniline reacts with NaNO2 and HCl to form benzene diazonium chloride.
2. Benzene diazonium chloride is reduced by H3PO2 and water to form benzene.
3. Benzene reacts with CO and HCl in the presence of AlCl3 and CuCl to form benzaldehyde.