ABSTRACT
The reaction with the metal and hydrogen gas leads to a complex, and after the transfer of hydrogen atoms to the carbon atom of a π-bond from the complex, the metal is free to react with more hydrogen gas and the alkene or alkyne is further reduced. The expensive metals used as catalysts are finely divided since catalytic hydrogenation occurs in heterogeneous systems as a surface reaction. Reduction reactions are extremely important in organic chemistry. A molecule, such as an aldehyde or ketone, in a higher oxidation state is converted to an alcohol, which is in a lower oxidation state. It is also possible to prepare alcohols by reduction of carboxylic acids. Dissolving metal reductions occur by an initial electron transfer from the metal. The mechanism involves the initial formation of a radical species, proton transfer from ammonia or ethanol, a subsequent second electron transfer that converts a radical to a carbanion, and a final proton transfer giving the product.
