Hydrogenation

Hydrogenation is the process of adding hydrogen to organic compounds. It is done to alkenes.

Vegetable oils have alkenes in them. Alkenes are liquid and spoil easily. People making shortening add hydrogen to the alkene, turning it into an alkane. The alkanes are more solid and stable. A catalyst is used to react the hydrogen with the oil. This makes trans fats, though. Margarine is an example of a hydrogenated spread.

Other things can be hydrogenated, too. Hot nitrogen is reacted with hydrogen under high pressure with a catalyst, usually nickel to make ammonia gas.

Hydrogenation Media

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  Steps in the hydrogenation of a C=C double bond at a catalyst surface, for example Ni or Pt :*(1) The reactants are adsorbed on the catalyst surface and H2 dissociates.*(2) An H atom bonds to one C atom. The other C atom is still attached to the surface.*(3) A second C atom bonds to an H atom. The molecule leaves the surface.

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  Mechanism for the hydrogenation of a terminal alkene using Wilkinson's catalyst.

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  The transition state of two transfer-hydrogenation reactions from ruthenium-hydride complexes onto carbonyls

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  Partial hydrogenation of a typical plant oil to a typical component of margarine. Most of the C=C double bonds are removed in this process, which elevates the melting point of the product.

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  Base-catalyzed hydrogenation of ketones.

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  Metal free hydrogenation Phosphine Borane

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  Dichlorotris(triphenylphosphine)ruthenium(II) is a precatalyst based on ruthenium.

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  Crabtree's catalyst is a highly active catalyst featuring iridium.

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  Cyclooctadiene rhodium chloride dimer, Rh
  2Cl
  2(cod)
  2 is a precursor to many homogeneous catalysts.

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  (S)-iPr-PHOX is a typical chelating phosphine ligand used in asymmetric hydrogenation.