Question

\( CH_3C \equiv CCH_3 \xrightarrow{(i)\,X \; (ii)\,H_2O/Zn} CH_3CO - COCH_3 \)
In the above reaction \( X \) is:

• A. \(HNO_3\)
• B. \(O_2\)
• C. \(O_3\)
• D. \(KMnO_4\)

Hint:

Alkyne + \(O_3/Zn,H_2O\) → diketone. Alkyne + hot \(KMnO_4\) → carboxylic acids.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
The reaction shows the conversion of an alkyne (But-2-yne) into a 1,2-diketone (Butane-2,3-dione). This is the standard outcome of the ozonolysis of an internal alkyne followed by mild reductive workup.
Step 2: Detailed Explanation:
1. Alkynes react with ozone (\( \text{O}_{3} \)) to form an intermediate ozonide.
2. When the ozonide is treated with water in the presence of zinc (\( \text{Zn} \)), it undergoes reductive cleavage.
3. For internal alkynes like \( \text{CH}_{3}\text{C} \equiv \text{CCH}_{3} \), the triple bond is partially cleaved. Unlike alkenes (which break completely into two molecules), alkynes typically produce \( \alpha \)-diketones if the workup is careful.
\[ \text{CH}_{3}-\text{C} \equiv \text{C}-\text{CH}_{3} + \text{O}_{3} \to \text{Ozonide} \xrightarrow{\text{Zn/H}_{2}\text{O}} \text{CH}_{3}-\text{C}(=\text{O})-\text{C}(=\text{O})-\text{CH}_{3} \]
Therefore, the reagent X is Ozone (\( \text{O}_{3} \)).
Step 3: Final Answer:
Reagent X is \( \text{O}_{3} \).