Predict the product 'B' in the sequence of reaction `HC -= CH overset (30% H_(2) SO_(4))underset(Hg So_(4)) to A overset (NaOH) to B`

Options

A. `CH_(3) COONa`
B. `CH_(3) COOH`
C. `CH_(3) CHO`
D. `CH_(3) - CH = CH - CHO`

Answer

To predict the product 'B' in the given sequence of reactions, let's break down the steps involved:

### Step 1: Reaction of Acetylene with H2SO4 and HgSO4
The starting compound is acetylene (HC≡CH). When acetylene reacts with 30% H2SO4 in the presence of HgSO4, it undergoes hydration. The reaction can be summarized as follows:

- The addition of water across the triple bond leads to the formation of an aldehyde.
- Since acetylene is a symmetrical terminal alkyne, the product formed is acetaldehyde (CH3CHO).

**Product A:** CH3CHO (Acetaldehyde)

### Step 2: Aldol Condensation with NaOH
Next, we take the product A (acetaldehyde) and react it with sodium hydroxide (NaOH). This reaction is an aldol condensation:

1. **Formation of Enolate Ion:**
- The base (NaOH) abstracts an alpha-hydrogen from the acetaldehyde, forming an enolate ion.

2. **Nucleophilic Addition:**
- The enolate ion then attacks the carbonyl carbon of another molecule of acetaldehyde, leading to the formation of a β-hydroxyaldehyde (aldol).

**Intermediate Product:** CH3CH(OH)CH2CHO (3-Hydroxybutanal)

3. **Dehydration:**
- The β-hydroxyaldehyde undergoes dehydration (loss of water) to form an α,β-unsaturated aldehyde.

**Final Product B:** CH3CH=CHCHO (But-2-enal or Crotonaldehyde)

### Summary of Products:
- **Product A:** Acetaldehyde (CH3CHO)
- **Product B:** But-2-enal (CH3CH=CHCHO)