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Alkyne Reactions: Alkyne Reduction using Lindlars Catalyst and H2

Lindlars catalyst and hydrogen gas (H2) will react with alkynes to form alkenes:

Alkyne Reactions: Alkyne Reduction using Lindlars Catalyst and H2 image3.png

The H2 and alkyne are adsorbed onto the surface of Lindlars catalyst. This reaction adds a hydrogen to each carbon on the alkyne bond, reducing the bond to an alkene bond. The hydrogens are added in a cis fashion, not trans:

Cis Addition

Alkyne Reactions: Alkyne Reduction using Lindlars Catalyst and H2 image2.png

NOT trans Addition

Alkyne Reactions: Alkyne Reduction using Lindlars Catalyst and H2 image1.png

The reaction mechanism is depicted below:

Alkyne Reactions: Alkyne Reduction using Lindlars Catalyst and H2 image4.png

In the first step, the H2 and alkyne adsorb to Lindlars catalyst, which catalyzes the reaction.

In the second step, the alkyne bond is able to react with H2, resulting in a cis addition of hydrogen to each carbon atom and the reduction of the triple bond to a double bond.

The reagent used for this reaction is H2 with Lindlars catalyst, represented by Pd in the mechanism figure.