The conversion of ethylene to ethyne involves

Options

A. `Br_(2)` treatment followed by aqueous KOH reaction
B. Alcoholic KOH treatment followed by `Br_(2)` reaction
C. `Br_(2)` treatment followed by alcoholic KOH reaction
D. Oxidation followed by reduction

Answer

To convert ethylene (C2H4) to ethyne (C2H2), we can follow these steps:

### Step 1: Bromination of Ethylene
- Ethylene (C2H4) reacts with bromine (Br2).
- The double bond in ethylene opens up, allowing bromine atoms to add across the double bond.
- This reaction produces 1,2-dibromoethane (C2H4Br2).

**Chemical Reaction:**
\[ \text{C}_2\text{H}_4 + \text{Br}_2 \rightarrow \text{C}_2\text{H}_4\text{Br}_2 \]

### Step 2: Dehydrohalogenation
- The next step involves treating 1,2-dibromoethane with alcoholic potassium hydroxide (KOH).
- This reaction leads to the elimination of hydrogen bromide (HBr) and results in the formation of a triple bond.
- The product of this reaction is ethyne (C2H2).

**Chemical Reaction:**
\[ \text{C}_2\text{H}_4\text{Br}_2 + \text{KOH (alc)} \rightarrow \text{C}_2\text{H}_2 + 2\text{HBr} + 2\text{KBr} \]

### Conclusion
Thus, the conversion of ethylene to ethyne involves bromination followed by treatment with alcoholic KOH. Therefore, the correct answer is:

**Option 3: Br2 treatment followed by alcoholic KOH reaction.**

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