When but-1-yne is treated with aqueous `H_(2)SO_(4)` in presence of `HgSO_(4)` , the major product is __________.

Options

A. `CH_(3)-CH_(2)-CH_(2)-CHO`
B. `CH_(3)-CH_(2)-CO-CH_(3)`
C. `CH_(3)-CH_(2)-CH=CH_(2)`
D. `CH_(3)-CH_(2)-CH_(2)-CH_(2)-OH`

Answer

To solve the problem of what major product is formed when but-1-yne is treated with aqueous H₂SO₄ in the presence of HgSO₄, we can follow these steps:

### Step 1: Understand the Reaction Conditions
When but-1-yne (a terminal alkyne) is treated with aqueous sulfuric acid (H₂SO₄) in the presence of mercuric sulfate (HgSO₄), it undergoes hydration. This reaction is known as the Markovnikov addition of water to the alkyne.

**Hint:** Remember that in hydration reactions involving alkynes, the addition follows Markovnikov's rule, where the more substituted carbon atom receives the hydroxyl group (OH).

### Step 2: Identify the Structure of But-1-yne
But-1-yne has the following structure:
- CH₃-CH₂-C≡C-H

**Hint:** Draw the structure of but-1-yne to visualize the position of the triple bond.

### Step 3: Add Water (H₂O) to the Alkyne
In the presence of H₂SO₄ and HgSO₄, water adds across the triple bond. The hydrogen (H) from water will add to the terminal carbon (less substituted), while the hydroxyl group (OH) will add to the more substituted carbon.

The reaction can be represented as:
- CH₃-CH₂-C≡C-H + H₂O → CH₃-CH₂-C(OH)=C-H (enol form)

**Hint:** Identify which carbon is more substituted and which is less substituted to apply Markovnikov's rule correctly.

### Step 4: Tautomerization
The enol formed (CH₃-CH₂-C(OH)=C-H) is not the stable form. It undergoes tautomerization to form the more stable keto form. This involves the migration of a hydrogen atom and the conversion of the double bond.

The tautomerization leads to:
- CH₃-CH₂-C(=O)-CH₃ (keto form)

**Hint:** Tautomerization is a common process in organic chemistry where an enol converts to a keto form, often resulting in a more stable product.

### Step 5: Identify the Major Product
The final product after tautomerization is:
- CH₃-CH₂-CO-CH₃

This corresponds to the structure of butan-2-one.

**Hint:** Compare the final product with the options given in the question to find the correct match.

### Conclusion
The major product formed when but-1-yne is treated with aqueous H₂SO₄ in the presence of HgSO₄ is **butan-2-one**, which corresponds to option B: CH₃-CH₂-CO-CH₃.

**Final Answer:** B) CH₃-CH₂-CO-CH₃