What is the Difference Between Hydrogenation and Hydrogenolysis?

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Hydrogenation and hydrogenolysis are both chemical reactions that involve the addition of hydrogen to organic compounds. However, they differ in the type of bond transformations that occur during the reactions:

  • Hydrogenation: This is a reaction where hydrogen is added to a molecule without cleaving any bonds. It occurs in compounds containing double or triple bonds and results in the reduction and saturation of the compounds. Hydrogenation is commonly used in the food industry and the petrochemical industry for various applications, such as hardening fats or upgrading oils.
  • Hydrogenolysis: This is a chemical reaction where a carbon-carbon or carbon-heteroatom single bond is cleaved or undergoes "lysis" by hydrogen. The heteroatom may vary, but it usually is oxygen, nitrogen, or sulfur. Hydrogenolysis involves bond cleavage and is often conducted catalytically using hydrogen gas. It is used in the petrochemical industry to remove sulfur from feedstock in petroleum refineries, for example.

In summary, the main difference between hydrogenation and hydrogenolysis lies in the fact that hydrogenation does not involve bond cleavage, while hydrogenolysis does. Both reactions occur in the presence of molecular hydrogen and require a catalyst.

Comparative Table: Hydrogenation vs Hydrogenolysis

The main difference between hydrogenation and hydrogenolysis is that hydrogenation involves the addition of hydrogen without cleaving bonds, while hydrogenolysis involves the addition of hydrogen with the cleavage of bonds. Here is a comparison table of the two processes:

Feature Hydrogenation Hydrogenolysis
Definition A chemical reaction where hydrogen gas is added to an organic compound, mainly involving bond formation. A reaction where a carbon-carbon or carbon-heteroatom bond is cleaved by hydrogen.
Reactants Typically alkenes (unsaturated compounds with double bonds). Oxygenated compounds, such as esters, lignin derivates, and furfural.
Products Saturated hydrocarbons or compounds with new bond formations. Deoxygenated products, such as hydrocarbons or other compounds with cleaved bonds.
Catalysts Often requires a catalyst, such as nickel, platinum, or palladium. Catalysts vary depending on the substrate, but hydrotreating catalysts are commonly used.
Examples Partial hydrogenation of alkynes, hydrogenation of aromatic rings. Hydrodeoxygenation of esters, lignin derivates, and furfural.

Both hydrogenation and hydrogenolysis are important processes in various industries, including the production of fuels, chemicals, and pharmaceuticals. The choice between the two processes depends on the desired product and the specific substrate involved.