English

Noun

hydrogenolysis

1. the cleavage of a molecule, especially that of a carbon-carbon bond, with the addition of hydrogen atoms to the fragments

Hydrogenolysis is a catalytic chemical reaction whereby a molecule of hydrogen is added over a carbon-heteroatom single bond, effectively causing a "lysis" of the bond. The heteroatom may vary, but usually is oxygen, nitrogen or sulfur. A closely related reaction is hydrogenation, where hydrogen is added over a carbon-carbon double bond (leading to the ultimate reduction to a single bond).

A classic example of hydrogenolysis is debenzylation - the removal of a benzyl protecting group usually attached to an oxygen or a nitrogen atom .

With the current knowledge, the only definitive statement that can be made about the ease of hydrogenolysis is that presence of a positive charge (formal or partial) on the heteroatom greatly increases the rate of hydrogenolysis. A proposed mechanism is presented in the hydrogenation article.

A commercial large-scale example of hydrogenolysis is the Raney Nickel catalyzed "desulfurization" of substituted thiophene rings, which is a general method for the synthesis of certain hydrocarbons.

The term was coined by Homer Burton Adkins.

Use in industry

The catalytic hydrogenation of organic sulfur compounds to form gaseous hydrogen sulfide (H2S) is very widely used in petroleum refineries, petrochemical plants and other industries to desulfurize various final products, intermediate products and process feedstocks by converting sulfur compounds to gaseous hydrogen sulfide which is then easily removed by distillation. The gaseous hydrogen sulfide is subsequently recovered in an amine treater and finally converted to elemental sulfur in a Claus process unit. In those industries, desulfurization process units are often referred to as hydrodesulfurizers (HDS) or hydrotreaters (HDT). In the petroleum refining and petrochemical industries, cobalt-molybdenum or nickel-molybdenum catalysts are commonly used for hydrogenation and hydrogenolysis catalysts.

References