Lindlar catalyst

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Lindlar catalyst

A Lindlar catalyst is a catalyst for the stereospecific hydrogenation of alkynes to alkenes . The Lindlar catalyst uses palladium as a catalyst and calcium carbonate as a carrier. The hydrogen is fed into the reactor in gaseous form. To prevent further hydrogenation to the alkane , lead acetate (or lead (II) oxide ) is used as a catalyst poison. This reduces the reactivity to such an extent that the alkene does not react any further. The catalyst is named after Herbert Lindlar ( Hoffmann-La Roche ).

Manufacturing

According to the description of the inventor, the catalyst is produced by reducing palladium (II) chloride in a slurry of calcium carbonate . A first deactivation takes place by adding lead acetate, after which it is deactivated further with quinoline , which increases the selectivity again. The selective hydrogenation of an alkyne to a styrene derivative is described.

properties

The Lindlar catalyst (also known as palladium on calcium carbonate, poisoned ) is a dark gray solid. The hydrogenation of alkynes with Lindlar catalysts always results in cis -alkenes, since in the first reaction step the alkyne is bound to the metallic palladium. Then, in the second step, an H 2 molecule is bound directly to the triple bond in an electrophilic addition reaction. As a result, both hydrogen atoms are added simultaneously and on the same side of the double bond. The alkene formed then dissolves from the palladium.

use

Example of the reaction of phenylacetylene to styrene

Examples are the reaction of phenylacetylene to styrene or the synthesis of vitamin A , in which a triple bond is selectively hydrogenated to a ( Z ) -alkene with a Lindlar catalyst .

recycling

Recycling this catalyst is sometimes difficult because it has to be thermally processed. The resulting exhaust gases sometimes contain poisonous lead oxides that some scrubber systems cannot hold back. Therefore, additional chemicals must be fed into the scrubber circuit, which can precipitate heavy metals (e.g. lead or mercury ).

Individual evidence

  1. ↑ a b Lindlar, H .; Dubuis, R .: Palladium Catalyst for Partial Reduction of Acetylenes In: Organic Syntheses . 46, 1966, p. 89, doi : 10.15227 / orgsyn.046.0089 ; Coll. Vol. 5, 1973, p. 880 ( PDF ).
  2. ↑ Lindlar, H. A New Catalyst for Selective Hydrogenations. In: Helv Chim Acta 1952, 35 , pp. 446-450. doi : 10.1002 / hlca.19520350205 .
  3. ↑ Data sheet Lindlar catalyst from Sigma-Aldrich , accessed on June 14, 2011 ( PDF ).Template: Sigma-Aldrich / name not given
  4. ↑ Overman, LE; Brown, MJ; McCann, SF: (Z) -4- (Trimethylsilyl) -3-buten-1-ol In: Organic Syntheses . 68, 1990, p. 182, doi : 10.15227 / orgsyn.068.0182 ; Coll. Vol. 8, 1993, p. 609 ( PDF ).

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