Partial Reduction of Alkynes with Lindlar Catalyst
Partial Reduction of Alkynes with Lindlar Catalyst: The Lindlar reduction converts an alkyne into an alkene without reducing it all the way to an alkane.
What happens
The Lindlar reduction converts an alkyne into an alkene without reducing it all the way to an alkane. Only one π bond is removed (C≡C → C=C). Lindlar catalyst is typically palladium on calcium carbonate (Pd/CaCO₃) treated with substances that decrease the activity of the palladium. To predict the product: change C≡C to C=C, add one H to each alkyne carbon, and put the H atoms on the same side; an internal alkyne gives the cis (Z) alkene.
Reaction summary
Alkyne + H₂ (Lindlar catalyst) → cis (Z) alkene (C≡C → C=C, syn addition)
Reagents and conditions
- Starting material: 2-Butyne (internal alkyne)
- Reagents: H₂, Lindlar catalyst
- Products: (Z)-2-Butene (cis alkene)
Selectivity
- Stereoselectivity: Syn addition: both H atoms are added from the same side, so an internal alkyne gives the cis (Z) alkene. This is the most important feature of the reaction.
Common mistakes
- Don't draw the alkane. Lindlar is specifically used for partial reduction, C≡C → C=C, not C≡C → C–C. Also remember: Lindlar = SYN, not anti.
Memory trick
Lindlar = Lovers. The two hydrogens want to stay together on the same side.