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Chemistry LibreTexts

21.7: Reduction of Carbonyl Compounds and Acid Chlorides Through Catalytic Hydrogenation

  • Page ID
    216886
  • Another way to reduce carbonyl groups and acid chlorides is through the catalytic addition of hydrogen. Just like the C=C bond, the C=O bond is capable of adding one mole of hydrogen. The catalyst typically used to accomplish this is called Raney Nickel.

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    If there are any C=C bonds present in the molecule, obviously they will also take up hydrogen. If selective reduction of the carbonyl group is desired, use NaBH4 instead.

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    As with the case of hydride reductions, the above reactions also go through the aldehyde stage, but cannot stop due to the high reactivity of the H2 /catalyst mixture. However, just as was the case in the addition of hydrogen to triple bonds, the process can be stopped at the aldehyde stage by the use of a reduced reactivity version of the H2 /catalyst mixture. This is accomplished by the addition of a “poison,” just as it was done with alkynes to stop at the alkene stage. It turns out that Lindlar’s catalyst works in this case as well.

    "Poisoned" catalysts for hydrogenation

    Pd / BaSO4 / S      Pd / BaSO4 / quinoline (Lindlar's catalyst)

    EXAMPLE:

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