Reduction of Unsaturated Compounds (DP IB Chemistry): Revision Note

Reduction of unsaturated compounds

Reduction of alkenes

• Alkenes are very useful compounds as they can undergo many types of reactions

• They can therefore be used as starting molecules when making new compounds

• The reaction between an alkene and hydrogen is known as hydrogenation or reduction

  • This requires a nickel catalyst, a temperature of 200 °C and a pressure of 1000 kPa

The reduction of ethene to ethane

Reduction of alkynes

• Similarly, alkynes, C_nH_2n-2 , can be reduced to alkenes, C_nH_2n , and alkanes, C_nH_2n+2 

• The number of hydrogen molecules required to fully saturate an organic compound depends on the number of multiple bonds it contains

Reduction of alkynes to alkenes and alkanes

• One important application of this reaction is in the production of margarine from vegetable oils

• Vegetable oils are unsaturated and can be hydrogenated to raise their melting point

  • This is due to stronger London Dispersion Forces, caused by increased surface contact between saturated hydrocarbon chains

• By controlling the hydrogenation conditions, some C=C bonds can remain

  • This produces partially hydrogenated vegetable oils with the ideal texture and consistency for margarine.