Question

In which of the following reaction Lindlar's catalyst is used?

• A. \( {CH}_3{CH} = {CH}{CH}_3 + H_2 \rightarrow {CH}_3{CH}_2{CH}_2{CH}_3 \)
• B. \( {CH}_3{CO}{CH}_3 + H_2 \rightarrow {CH}_3{CH(OH)}{CH}_3 \)
• C. \( {CH}_3{CH}_2{NO}_2 + H_2 \rightarrow {CH}_3{CH}_2{NH}_2 \)
• D. \( {C}_6{H}_5{CHO} + H_2 \rightarrow {C}_6{H}_5{CH}_2{OH} \)
• E. \( {CH}_3{C} = {C}{CH}_3 + H_2 \rightarrow {CH}_3{CH} = {CH}{CH}_3 \)

Hint:

Lindlar’s catalyst is specifically used for the partial hydrogenation of alkynes to form cis-alkenes. It is useful when selective reduction is required without reducing the alkyne all the way to an alkane.

Answer 1

Answer: (E)

Lindlar’s catalyst is used for the hydrogenation of alkynes to cis-alkenes. This catalyst is specifically designed to selectively hydrogenate alkynes without reducing them to alkanes. It does this by allowing the addition of hydrogen across the triple bond to form a cis-alkene.
In the given reactions:
- Option (A): This is a typical hydrogenation reaction, but it is not a case where Lindlar's catalyst is used.
- Option (B): This reaction involves the reduction of a ketone to an alcohol, which does not require Lindlar's catalyst.
- Option (C): This reaction involves the reduction of a nitro group to an amine, which also does not require Lindlar's catalyst.
- Option (D): This is a reduction of an aldehyde to a primary alcohol, which does not involve Lindlar’s catalyst.
- Option (E): This reaction shows the hydrogenation of an alkyne (\( {CH}_3{C} = {C}{CH}_3 \)) to a cis-alkene (\( {CH}_3{CH} = {CH}{CH}_3 \)), which is exactly the type of reaction Lindlar's catalyst is used for.
Thus, the correct answer is option (E), \( {CH}_3{C} = {C}{CH}_3 + H_2 \rightarrow {CH}_3{CH} = {CH}{CH}_3 \).