Hydrogenolysis is achemical reaction whereby acarbon–carbon or carbon–heteroatom single bond is cleaved or undergoeslysis (breakdown) byhydrogen.[1] The heteroatom may vary, but it usually is oxygen, nitrogen, or sulfur. A related reaction ishydrogenation, where hydrogen is added to the molecule, without cleaving bonds. Usually hydrogenolysis is conducted catalytically using hydrogen gas.
The term "hydrogenolysis" was coined byCarleton Ellis in reference to hydrogenolysis of carbon–carbon bonds.[1][2] Earlier,Paul Sabatier had already observed the hydrogenolysis ofbenzyl alcohol totoluene,[3] and as early as 1906, Padoa and Ponti had observed the hydrogenolysis offurfuryl alcohol.[4]Homer Burton Adkins andRalph Connor were the first to call the carbon–oxygen bond cleavage "hydrogenolysis".[1]
Inpetroleum refineries, catalytic hydrogenolysis of feedstocks is conducted on a large scale to remove sulfur from feedstocks, releasing gaseoushydrogen sulfide (H2S). The hydrogen sulfide is subsequently recovered in anamine treater and finally converted to elementalsulfur in aClaus process unit. In those industries, desulfurization process units are often referred to ashydrodesulfurizers (HDS) orhydrotreaters (HDT). Catalysts are based onmolybdenum sulfide containing smaller amounts of cobalt or nickel. Hydrogenolysis is accompanied by hydrogenation.[5]
Another hydrogenolysis reaction of commercial importance is the hydrogenolysis of esters into alcohols by catalysts such ascopper chromite.
Thehydrodeoxygenation reaction used in theNeste Renewable Diesel process, thevegetable oil refining process of largest production capacity, is a hydrogenolysis oftriglycerides intoalkanes.
In the laboratory, hydrogenolysis is used inorganic synthesis. Debenzylation is most common and involves the cleavage ofbenzyl ethers:[6]
Thioketals undergo hydrogenolysis usingRaney nickel in theMozingo reduction.
Laboratory hydrogenolysis is operationally similar tohydrogenation, and may be accomplished at atmospheric pressure by stirring the reaction mixture under a slight positive pressure of hydrogen gas, having flushed the apparatus with more of this gas. The hydrogen may be provided by attaching a balloon to a needle, filling it from a bottle, and inserting the needle into the reaction flask via arubber septum. At high pressure, a hydrogenationautoclave (i.e., a Buchi or Parrhydrogenator) or similar piece of equipment is required.