Lindlar hydrogenation
Alkynes are partly hydrogenated to alkenes over palladised charcoal partially deactivated with poisons such as quinoline or BaSO4.
EthyneHC≡CHAlkyne - Step 1
H₂, Pd/C, quinoline
EtheneCH₂=CH₂Alkene
How it works
- Hydrogen adds to the alkyne on the poisoned catalyst surface.
- The poisoned catalyst is too weak to reduce the alkene.
- The cis alkene forms from a disubstituted alkyne.
What it makes
Alkenes from alkynes (cis alkenes from internal alkynes).
Where it fails
Hydrogenation over Ni or Pt goes to the alkane. Na in liquid NH3 gives the trans alkene instead.
Class 11, Chapter 9 Hydrocarbons
Lindlar hydrogenation: quick answers
What is the Lindlar catalyst?
Palladised charcoal partially deactivated with poisons.
What does Na in liquid NH3 give?
The trans alkene.
Why does it stop at the alkene?
The poisoned catalyst cannot reduce the less reactive alkene.