Kerala KEAM 5 June 2024 Solved Paper

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 ($CH_3C = CCH_3$) to a cis-alkene ($CH_3CH = CHCH_3$), which is exactly the type of reaction Lindlar's catalyst is used for.Thus, the correct answer is option (E), $CH_3C = CCH_3 + H_2 \rightarrow CH_3CH = CHCH_3$. Quick Tip: 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.