Addition of water to phenyl acetylene in presence of dil. `H_2SO_4` and `HgSO_4` give ______

Answer

To solve the question regarding the addition of water to phenyl acetylene in the presence of dilute H₂SO₄ and HgSO₄, we can break it down into the following steps:

### Step-by-Step Solution:

1. **Identify the Reactants**:
- The reactant is phenyl acetylene, which has the structure C₆H₅-C≡C-H (a phenyl group attached to an alkyne).
- The reagents used are dilute sulfuric acid (H₂SO₄) and mercuric sulfate (HgSO₄).

2. **Understand the Reaction Conditions**:
- The presence of dilute H₂SO₄ and HgSO₄ indicates that we are performing a hydration reaction. The mercuric sulfate acts as a catalyst in this reaction.

3. **Mechanism of the Reaction**:
- The alkyne (phenyl acetylene) undergoes electrophilic addition. The triple bond (C≡C) reacts with water (H₂O) in the presence of the acid and mercury salt.
- The first step involves the formation of a mercuric alkyne intermediate. The triple bond attacks the mercury ion, forming a vinyl cation.

4. **Formation of the Product**:
- The vinyl cation then reacts with water, leading to the formation of an enol (which has a double bond and an alcohol group).
- The enol is unstable and quickly tautomerizes to form a ketone.

5. **Final Product**:
- The final product of this reaction is acetophenone, which has the structure C₆H₅-C(=O)-CH₃. This is because the addition of water results in the formation of a carbonyl group (C=O) adjacent to the phenyl group.

### Conclusion:
The addition of water to phenyl acetylene in the presence of dilute H₂SO₄ and HgSO₄ gives **acetophenone**.

---