Question
How are alkenes prepared from Alkynes ?
Solution
Alkenes are prepared by the partial reduction of alkynes.
(a) Using Lindlar’s catalyst. Catalytic reduction of alkynes in the presence of palladium catalyst deposited over BaSO4 or CaSO4 and partially poisoned by S or quinoline (Lindlar’s catalyst) predominantly gives us alkenes.
(b) Using Birch reduction. If alkynes are reduced by sodium and liquid ammonia (Birch reduction), trans-alkenes are major products. 
