`CH_(3)COOH overset((i) PCl_(3)+Cl_(2) ("excess"))underset((ii) O_(2))to (X) overset(SOCl_2) to (Y) overset(H_(2)//Pd//BaSO_(4))to(Z) overset(OH^(-))to W+S `
Write the structure of X,Y,Z , W and S

Answer

To solve the problem step by step, we will analyze each reaction and determine the structures of the compounds X, Y, Z, W, and S formed during the reactions of acetic acid (CH₃COOH).

### Step 1: Reaction of CH₃COOH with PCl₃ and Cl₂ (excess) to form X
The first reaction involves acetic acid (CH₃COOH) reacting with phosphorus trichloride (PCl₃) and chlorine (Cl₂) in excess. This is known as the HVZ reaction (Hunsdiecker reaction).

**Resulting Compound (X):**
The product formed is chloroacetic acid (ClCH₂COOH).

**Structure of X:**
```
Cl
|
H2C - C - OH
||
O
```

### Step 2: Reaction of X with SOCl₂ to form Y
Next, chloroacetic acid (X) reacts with thionyl chloride (SOCl₂). This reaction converts the carboxylic acid group into an acyl chloride.

**Resulting Compound (Y):**
The product formed is acetyl chloride (CH₃COCl).

**Structure of Y:**
```
Cl
|
H3C - C
||
O
```

### Step 3: Reaction of Y with H₂/Pd/BaSO₄ to form Z
The acetyl chloride (Y) then undergoes reduction in the presence of hydrogen gas (H₂) and a palladium catalyst supported on barium sulfate (BaSO₄). This is a Rosenmund reduction.

**Resulting Compound (Z):**
The product formed is acetaldehyde (CH₃CHO).

**Structure of Z:**
```
H
|
H3C - C
||
O
```

### Step 4: Reaction of Z with OH⁻ to form W and S
Finally, acetaldehyde (Z) reacts with hydroxide ions (OH⁻) in a reaction known as aldol condensation. This reaction typically leads to the formation of β-hydroxy aldehydes or ketones.

**Resulting Compound (W):**
The product formed is 3-hydroxybutanal (W), which has both an aldehyde and an alcohol functional group.

**Structure of W:**
```
H
|
H2C - C - OH
| ||
O O
```

**Resulting Compound (S):**
The byproduct (S) of this reaction is hydrochloric acid (HCl).

### Summary of Structures:
- **X:** Chloroacetic acid (ClCH₂COOH)
- **Y:** Acetyl chloride (CH₃COCl)
- **Z:** Acetaldehyde (CH₃CHO)
- **W:** 3-Hydroxybutanal (C₄H₈O₂)
- **S:** Hydrochloric acid (HCl)