Addition of Hydrogen Hydrogen in the presence of a catalyst will add twice to alkynes to generate alkanes. H H2,Pt H,Pt R-C=C一RM H H This reaction proceeds through a cis alkene intermediate,but cannot be stopped at this stage except with the use of a special catalyst. H-C=C-CH2CHs +2H2R,H-CH2-CH2- CH2CH3 but-1-yne butan (100% CH3-C=C-CH3 +2H2>CH3-CH2-CH2-CH3 but-2-yne butane (100%) The special catalyst is:Lindlar's catalyst This is a partially deactivated(poisoned)catalyst consisting of barium sulfate,palladium and quinoline(the poison). H2,Pd/BaSO4 R-C≡C-R' Quinoline,CH3OH R The hydrogens are delivered simultaneously to the same side of the alkyne,creating syn addition(cis alkenes). Ch09 Alkynes (landscape) Page 10 Ch09 Alkynes (landscape) Page 10 Addition of Hydrogen Hydrogen in the presence of a catalyst will add twice to alkynes to generate alkanes. This reaction proceeds through a cis alkene intermediate, but cannot be stopped at this stage except with the use of a special catalyst. The special catalyst is: Lindlar’s catalyst This is a partially deactivated (poisoned) catalyst consisting of barium sulfate, palladium and quinoline (the poison). The hydrogens are delivered simultaneously to the same side of the alkyne, creating syn addition (cis alkenes). R C C R' H R H R' H2 , Pd/BaSO4 Quinoline, CH3OH