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Lindlar catalyst
Introduction
A Lindlar catalyst is a heterogeneous catalyst that consists of palladium deposited on calcium carbonate and treated with various forms of lead. The lead additive serves to deactivate the palladium sites. A variety of “catalyst poisons” have been used including lead acetate and lead oxide. The palladium content of the catalyst is usually 5% by weight. The catalyst is used for the hydrogenation of alkynes to alkenes.
As described by its inventor,[1][2] the catalyst is prepared by reduction of palladium chloride in a slurry of calcium carbonate followed by adding lead acetate. By this approach, one obtains a catalyst with a large surface area. Further deactivation of the catalyst with quinoline enhances its selectivity, preventing formation of alkanes. An example of alkyne reduction is the reduction of phenylacetylene to styrene.[1]
Alkyne reduction is stereoselective, occurring via syn addition to give the cis-alkene.[3] The commercial organic synthesis of vitamin A also involves an alkyne reduction with the Lindlar catalyst.
Other heterogeneous catalysts useful for hydrogenation are Adam’s Catalyst, Palladium Black, and Raney nickel.
References
- ↑ 1.0 1.1 Lindlar, H.; Dubuis, R. “Palladium Catalyst for Partial Reduction of Acetylenes” Organic Syntheses, Collected Volume 5, p.880 (1973).http://www.orgsyn.org/orgsyn/pdfs/CV5P0880.pdf
- ↑ Lindlar, H. “Ein neuer Katalysator für selektive Hydrierungen”; Helv. Chim. Acta 1952, 35, 446-450, doi:10.1002/hlca.19520350205.
- ↑ Overman, L. E.; Brown, M. J.; McCann, S. F. “(Z)-4-(Trimethylsilyl)-3-Buten-1-ol” Organic Syntheses, Collected Volume 8, p.609 (1993). http://www.orgsyn.org/orgsyn/pdfs/CV8P0609.pdf