Hydrogenolysis

Definition

Hydrogenolysis is a chemical reaction where a carbon-heteroatom bond, such as a carbon-oxygen or carbon-nitrogen bond, is cleaved by the addition of hydrogen. This process is commonly used in organic chemistry for the selective removal of protecting groups and the reduction of various functional groups.

5 Must Know Facts For Your Next Test

1. Hydrogenolysis is commonly used to selectively remove benzyl, tert-butyl, and silyl ether protecting groups in organic synthesis.
2. The reaction is typically carried out using hydrogen gas (H2) in the presence of a transition metal catalyst, such as palladium on carbon (Pd/C) or platinum oxide (PtO2).
3. Hydrogenolysis can be used to reduce alkyl halides, esters, and other functional groups by cleaving the carbon-heteroatom bond.
4. In the context of carbohydrate chemistry, hydrogenolysis can be used to remove benzyl protecting groups from polysaccharides, allowing for the synthesis of complex glycans.
5. The mechanism of hydrogenolysis typically involves the heterolytic cleavage of the carbon-heteroatom bond, where the hydrogen atom is added to the heteroatom, and the remaining fragment is released.

Review Questions

• Explain how hydrogenolysis is used in the reduction of alkenes (8.6 Reduction of Alkenes: Hydrogenation)
  • Hydrogenolysis is a key step in the reduction of alkenes to alkanes, known as hydrogenation. In this process, the addition of hydrogen gas (H2) in the presence of a transition metal catalyst, such as palladium or platinum, cleaves the carbon-carbon double bond of the alkene. The hydrogen atoms are then added to the carbon atoms, forming a saturated alkane product. This selective reduction of alkenes is an important transformation in organic synthesis, allowing for the controlled manipulation of carbon-carbon unsaturated bonds.
• Describe the role of hydrogenolysis in the reduction of alkynes (9.5 Reduction of Alkynes)
  • Hydrogenolysis can also be used to reduce alkynes to alkenes or alkanes. When an alkyne is subjected to catalytic hydrogenation conditions, the carbon-carbon triple bond is first reduced to an alkene intermediate through the addition of hydrogen. Further hydrogenolysis of the alkene can then cleave the remaining carbon-carbon double bond, ultimately yielding an alkane product. This stepwise reduction of alkynes is a valuable tool in organic synthesis, allowing for the selective transformation of triple bonds to single bonds while preserving other functional groups.
• Analyze how hydrogenolysis is involved in the oxidation and reduction of organic compounds (10.8 Oxidation and Reduction in Organic Chemistry)
  • Hydrogenolysis is a key reduction reaction in organic chemistry, as it allows for the selective cleavage of carbon-heteroatom bonds. This process can be used to reduce a variety of functional groups, such as esters, ethers, and halides, by breaking the carbon-oxygen or carbon-halogen bond and adding hydrogen. The ability to selectively reduce these groups while preserving other sensitive functionalities makes hydrogenolysis an important tool in the oxidation and reduction of organic compounds, enabling the controlled manipulation of molecular structures during organic synthesis.

Related terms

Catalytic Hydrogenation: A chemical reaction where hydrogen gas (H2) is added to a substrate in the presence of a catalyst, typically a transition metal, to reduce unsaturated bonds such as alkenes and alkynes.

Reductive Cleavage: The process of breaking a chemical bond by the addition of hydrogen, often used to remove protecting groups or reduce functional groups in organic synthesis.

Heterolytic Bond Cleavage: A type of bond cleavage where the bonding electrons are unequally distributed between the two atoms, resulting in the formation of a cation and an anion.