Question

Consider the following reaction
\[ \text{Propyne} + CH_3MgBr \xrightarrow{\text{dry ether}} X \]
Identify \( X \) from the following.

• A. But-2-yne
• B. Propane
• C. Methane
• D. But-2-ene

Hint:

Terminal alkynes behave as weak acids and react with Grignard reagents to give alkynyl magnesium halides along with methane formation.

Answer 1

The Correct Option is C

Step 1: Identify the nature of propyne.
Propyne \( (CH_3-C \equiv CH) \) is a terminal alkyne.
Terminal alkynes contain an acidic hydrogen atom attached to the \( sp \)-hybridised carbon.

Step 2: Understand the reagent.
\( CH_3MgBr \) is a Grignard reagent.
Grignard reagents behave as strong bases and can abstract acidic protons.

Step 3: Proton abstraction reaction.
The acidic hydrogen of propyne is removed by \( CH_3MgBr \):
\[ CH_3-C \equiv CH + CH_3MgBr \rightarrow CH_3-C \equiv C^-MgBr + CH_4 \]

Step 4: Identify the product formed.
The methyl group from Grignard reagent gains a proton and forms methane.

Step 5: Nature of final products.
Two products are formed:
(i) Acetylide salt \( CH_3-C \equiv C^-MgBr \)
(ii) Methane \( CH_4 \)
Among the given options, methane is the correct answer.

Step 6: Conclusion.
Thus, the product \( X \) is:
\[ \boxed{CH_4} \]