Lindlar catalyst
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A Lindlar catalyst is a palladium heterogeneous catalyst on calcium carbonate poisoned, deactivated, or conditioned by lead acetate, Pd - CaCO3 - Pb (CAS registry number 7440-05-3). In another Lindlar system the palladium is deactivated by lead oxide. The load of palladium is usually 5%. The catalyst is used in alkyne reduction.
The catalyst is prepared by reduction of palladium chloride in the presence of a slurry of calcium carbonate followed by adding lead acetate. By grafting palladium in this way to a solid substrate a large catalytically active surface area is obtained. The Lindlar catalyst is effective with hydrogen in the organic reduction of alkynes to alkenes. Deactivation of the catalyst with quinoline makes the catalyst very selective and the hydrogenation is not carried through to the alkane. Alkyne reduction is stereoselective with syn addition to the cis-alkene. The reason for this is that one face of the triple bond is shielded by the catalyst surface restricting access for the hydrogen molecule to the other side. An example of alkyne reduction is the reduction of phenylacetylene to styrene. The commercial organic synthesis of vitamin A also involves an alkyne reduction with the Lindlar catalyst.
Other heterogeneous hydrogenation catalysts are Adam's Catalyst, Palladium Black and Raney nickel . Homogeneous catalysts include Wilkinson's catalyst.
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[edit] References
- Lindlar, H.; Helv. Chim. Acta 1952, 35, 446.
- Palladium catalyst for the partial reduction of acetylenes H. Lindlar and R. Dubuis Organic Syntheses, Coll. Vol. 5, p.880; Vol. 46, p.89 Article
