Addition of water to ethyne in the presence of `H_2SO_4` and HgSO_4` gives

Options

A. Acetone
B. Acetaldehyde
C. Formaldehyde
D. Glyoxal

Answer

To solve the question regarding the addition of water to ethyne in the presence of H₂SO₄ and HgSO₄, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Reactants**:
The reactants are ethyne (C₂H₂), sulfuric acid (H₂SO₄), and mercury(II) sulfate (HgSO₄).

2. **Understand the Reaction Conditions**:
The reaction occurs under acidic conditions and at a temperature of 75 to 80 degrees Celsius.

3. **Apply Markovnikov's Rule**:
According to Markovnikov's rule, when water (H₂O) is added to an alkene or alkyne, the hydrogen atom from the water will attach to the carbon with the greater number of hydrogen atoms already attached. In the case of ethyne, both carbons are equivalent, but we will still follow the rule for the sake of understanding.

4. **Electrophilic Addition**:
The first step involves the protonation of ethyne by H⁺ from sulfuric acid. This results in the formation of a carbocation. The structure can be represented as:
\[ \text{C} \equiv \text{C} + \text{H}^+ \rightarrow \text{C}^+ - \text{C} \]

5. **Nucleophilic Attack by Water**:
Water (acting as a nucleophile) attacks the carbocation. This leads to the formation of an enol:
\[ \text{C}^+ - \text{C} + \text{H}_2\text{O} \rightarrow \text{CH}_2\text{CHOH} \]

6. **Tautomerization**:
The enol (CH₂CHOH) is less stable and undergoes tautomerization to form a more stable keto form. This involves the migration of a hydrogen atom and the rearrangement of bonds:
\[ \text{CH}_2\text{CHOH} \rightarrow \text{CH}_3\text{COOH} \]

7. **Final Product**:
The final product of the reaction is acetaldehyde (CH₃CHO) and the enol form (which is less stable).

### Conclusion:
The addition of water to ethyne in the presence of H₂SO₄ and HgSO₄ gives acetaldehyde (CH₃CHO) as the main product.