Is there any difference between the Lindlar and Rosenmund catalysts? I've checked around, and it seems the same compounds are used to make both. Is there a difference in their reactivities or are they essentially the same?
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asked Oct 10, 2016 at 3:18
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3$\begingroup$ The additive.$%stuff in comments =D$ $\endgroup$– JanCommented Oct 10, 2016 at 11:39
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2 Answers
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This is a rather interesting question because these names actually refer to classes of reactions (specific to certain reagents and products), and aren't constrained by specific proportions of substances or even the identity of these substances.
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A Rosenmund catalyst is used to reduce acyl chlorides to their corresponding aldehydes, and is typically composed of palladium supported on $\ce{BaSO4}$, and poisoned by sodium acetate, N,N-dimethylaniline, thiourea, thiophene, dibenzothiophene, ethyldiisopropyl amine, or, most commonly, quinoline.
A Lindlar catalyst is used to reduce alkynes to cis alkenes, and is typically composed of palladium supported on $\ce{BaCO3}$, $\ce{CaCO3}$, or carbon, and poisoned by lead acetate and quinoline.
The broad list of poisons which cause nearly identical catalytic activity of the supported palladium in both Lindlar and Rosenmund catalysts tells that the poisons are not involved in the catalytic process itself, but rather are affecting the surface of the catalyst. Interestingly, Lindlar-active palladium shows no activity for the conversion of benzoyl chloride to benzaldehyde under various conditions. This demonstrates that despite similar catalyst preparation procedures, the two reactions are catalyzed by different active sites.$^{[1]}$
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Lindlar catalyst: we see it was used in the preparation of alkenes from alkynes, where an alkyne is partially reduced with a calculated amount of dihydrogen in the presence of palladised charcoal $(\ce{Pd/C})$, and it is deactivated with poisons like sulfur compounds or quinoline give alkenes.
$$\ce{RC#CR' +H2 ->[Pd/C] RHC=CHR' (\text{cis-Alkene})}$$
Palladium on barium sulfate $(\ce{Pd-BaSO4})$ is sometimes called Rosenmund catalyst. This is used in Rosenmund reduction, where acyl chlorides leads to the preparation of an aldehyde.
These both catalysts have palladium in them but the compound used with it is different in both above cases. Thus we can conclude that these catalysts look similar, but they are not the same.
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2$\begingroup$ $\ce{R-H-C=C-H-R}$ does not make sense chemically. Also, why did you put the reaction arrow where it is? $\endgroup$– JanCommented Aug 10, 2017 at 10:26
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