9.4 Reduction of Alkynes

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    Catalytic Hydrogenation

    Less Substituted More Substituted
    Two Groups Added
    H
    H
    Reagents H2 / catalyst              catalyst = Pt, Pd, or Ni
    Regioselectivity n/a
    Stereospecificity Syn
    Other Characteristics Adds 2 equivalents of H2.
    Same reagents as with alkenes.
    catalytic hydrogenation
    catalytic hydrogenation of alkynes

    Catalytic Hydrogenation with a Poisoned Catalyst (like Lindlar's Catalyst)

    Less Substituted More Substituted
    Two Groups Added
    H
    H
    Reagents H2 / Lindlar’s catalyst
    Lindlar’s catalyst = Pd / BaSO4 / quinoline
    Regioselectivity n/a
    Stereospecificity Syn (forms a cis-alkene)
    Other Characteristics Adds only 1 equivalent of H2.
    Unreactive with alkenes.
    catalytic hydrogenation Lindlars

    Dissolving Metal Reduction

    Less Substituted More Substituted
    Two Groups Added
    H
    H
    Reagents Na / NH3(l)
    Works with Na, Li, or K
    Regioselectivity n/a
    Stereospecificity Anti (forms a trans-alkene)
    Other Characteristics Adds only 1 equivalent of H2.
    Unreactive with alkenes.
    dissolving metal reduction