Which of the following is Lindlar catalyst ?
Best answer
Answer: (2) Partially deactivated palladised charcoal
Lindlar's catalyst is palladium on a support (charcoal, \(\mathrm{CaCO_3}\) or \(\mathrm{BaSO_4}\)) that has been partly "poisoned" with lead acetate or quinoline. The poison lowers its activity so that an alkyne is hydrogenated only as far as the alkene:
\[\mathrm{R{-}C{\equiv}C{-}R + H_2 \xrightarrow{\text{Lindlar}} \textit{cis}\text{-}RCH{=}CHR}\]
It gives the cis alkene. (Sodium in liquid ammonia, option 4, reduces alkynes to trans alkenes instead.)
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