Phenylacetylene on treatment with `HgSO_(4)//H_(2)SO_(4), H_(2)O` produces

Options

A. Acetophenone
B. Phenylacetic acid
C. 1 - Phenylethanol
D. 2 - Phenyletharol

Answer

To solve the problem of what phenylacetylene produces when treated with `HgSO4`, `H2SO4`, and `H2O`, we can follow these steps:

### Step 1: Identify the Reactants
The reactant is phenylacetylene, which can be represented as:
\[ \text{Ph-C}\equiv\text{C-H} \]
where "Ph" stands for the phenyl group (C6H5).

### Step 2: Understand the Reaction Conditions
The reaction conditions involve mercuric sulfate (`HgSO4`), sulfuric acid (`H2SO4`), and water (`H2O`). This indicates that we are performing a hydration reaction of the alkyne (phenylacetylene) in the presence of a mercuric ion catalyst.

### Step 3: Apply Markovnikov's Rule
According to Markovnikov's rule, when water is added to an alkyne, the hydrogen atom (H) will attach to the carbon with more hydrogen atoms (the less substituted carbon), and the hydroxyl group (OH) will attach to the carbon with fewer hydrogen atoms (the more substituted carbon).

### Step 4: Form the Intermediate
When phenylacetylene reacts with the mercuric ion, a cyclic mercurinium ion intermediate is formed. This intermediate can be represented as:
\[ \text{Ph-C}^+\text{H-C}(\text{Hg}^{2+}) \]
The water molecule will then attack the more stable carbocation formed on the carbon adjacent to the phenyl group.

### Step 5: Determine the Stable Carbocation
In this case, the carbocation that forms on the carbon adjacent to the phenyl group is more stable due to resonance stabilization. Therefore, the water molecule will add to this carbon, leading to the formation of an enol intermediate:
\[ \text{Ph-C}(\text{OH})-\text{C}(\text{H}) \]

### Step 6: Tautomerization
The enol form will undergo keto-enol tautomerization, where the hydrogen atom from the hydroxyl group will shift to the adjacent carbon, leading to the formation of a ketone:
\[ \text{Ph-C}=\text{C(OH)-C}(\text{H}) \rightarrow \text{Ph-C(=O)-C}(\text{H}) \]
This results in the formation of acetophenone:
\[ \text{Ph-C(=O)-CH}_3 \]

### Final Answer
The product of the reaction of phenylacetylene with `HgSO4`, `H2SO4`, and `H2O` is **acetophenone**.

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