Hydrogenolysis is a

chemical reaction A chemical reaction is a process that leads to the chemical transformation of one set of chemical substances to another. Classically, chemical reactions encompass changes that only involve the positions of electrons in the forming and break ...

whereby a carbon–carbon or carbon–

heteroatom In chemistry, a heteroatom () is, strictly, any atom that is not carbon or hydrogen. Organic chemistry In practice, the term is usually used more specifically to indicate that non-carbon atoms have replaced carbon in the backbone of the molecul ...

single bond is cleaved or undergoes

lysis Lysis ( ) is the breaking down of the membrane of a cell, often by viral, enzymic, or osmotic (that is, "lytic" ) mechanisms that compromise its integrity. A fluid containing the contents of lysed cells is called a ''lysate''. In molecular bio ...

(breakdown) by

hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic ...

.Ralph Connor, Homer Adkins. Hydrogenolysis Of Oxygenated Organic Compounds. J. Am. Chem. Soc.; 1932; 54(12); 4678–4690. The heteroatom may vary, but it usually is oxygen, nitrogen, or sulfur. A related reaction is

hydrogenation Hydrogenation is a chemical reaction between molecular hydrogen (H2) and another compound or element, usually in the presence of a catalyst such as nickel, palladium or platinum. The process is commonly employed to reduce or saturate org ...

, where hydrogen is added to the molecule, without cleaving bonds. Usually hydrogenolysis is conducted catalytically using hydrogen gas.

History

The term "hydrogenolysis" was coined by Carleton Ellis in reference to hydrogenolysis of carbon–carbon bonds. Earlier, Paul Sabatier had already observed the hydrogenolysis of

benzyl alcohol Benzyl alcohol is an aromatic alcohol with the formula C6H5CH2OH. The benzyl group is often abbreviated "Bn" (not to be confused with "Bz" which is used for benzoyl), thus benzyl alcohol is denoted as BnOH. Benzyl alcohol is a colorless liqui ...

toluene Toluene (), also known as toluol (), is a substituted aromatic hydrocarbon. It is a colorless, water-insoluble liquid with the smell associated with paint thinners. It is a mono-substituted benzene derivative, consisting of a methyl group (CH3) ...

, and as early as 1906, Padoa and Ponti had observed the hydrogenolysis of

furfuryl alcohol Furfuryl alcohol is an organic compound containing a furan substituted with a hydroxymethyl group. It is a colorless liquid, but aged samples appear amber. It possesses a faint odor of burning and a bitter taste. It is miscible with but unstabl ...

. Homer Burton Adkins and Ralph Connor were the first to call the carbon–oxygen bond cleavage "hydrogenolysis".

In the petrochemical industry

In petroleum refineries, catalytic hydrogenolysis of feedstocks is conducted on a large scale to remove sulfur from feedstocks, releasing gaseous

hydrogen sulfide Hydrogen sulfide is a chemical compound with the formula . It is a colorless chalcogen-hydride gas, and is poisonous, corrosive, and flammable, with trace amounts in ambient atmosphere having a characteristic foul odor of rotten eggs. The und ...

(H₂S). The hydrogen sulfide is subsequently recovered in an

amine treater Amine gas treating, also known as amine scrubbing, gas sweetening and acid gas removal, refers to a group of processes that use aqueous solutions of various alkylamines (commonly referred to simply as amines) to remove hydrogen sulfide (H2S) and ...

and finally converted to elemental

sulfur Sulfur (or sulphur in British English) is a chemical element with the symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms form cyclic octatomic molecules with a chemical formul ...

in a Claus process unit. In those industries, desulfurization process units are often referred to as hydrodesulfurizers (HDS) or hydrotreaters (HDT). Catalysts are based on molybdenum sulfide containing smaller amounts of cobalt or nickel. Hydrogenolysis is accompanied by hydrogenation. Another hydrogenolysis reaction of commercial importance is the hydrogenolysis of esters into alcohols by catalysts such as copper chromite. The

hydrodeoxygenation Hydrodeoxygenation (HDO) is a hydrogenolysis process for removing oxygen from oxygen-containing compounds. Typical HDO catalysts commonly are sulfided nickel-molybdenum or cobalt-molybdenum on gamma alumina. An idealized reaction is: :R2O + ...

reaction used in the Neste Renewable Diesel process, the

vegetable oil refining Vegetable oil refining may refer to: * Fat hydrogenation, combining vegetable oil with hydrogen to make it more saturated * Edible oil refining, process to refin a raw oil to produce an edible oil, which differ from Olive oil production. * Biodi ...

process of largest production capacity, is a hydrogenolysis of

triglyceride A triglyceride (TG, triacylglycerol, TAG, or triacylglyceride) is an ester derived from glycerol and three fatty acids (from ''tri-'' and '' glyceride''). Triglycerides are the main constituents of body fat in humans and other vertebrates, as ...

s into

alkane In organic chemistry Organic chemistry is a subdiscipline within chemistry involving the science, scientific study of the structure, properties, and reactions of organic compounds and organic materials, i.e., matter in its various forms tha ...

In the laboratory

In the laboratory, hydrogenolysis is used in

organic synthesis Organic synthesis is a special branch of chemical synthesis and is concerned with the intentional construction of organic compounds. Organic molecules are often more complex than inorganic compounds, and their synthesis has developed into one o ...

. Debenzylation is most common and involves the cleavage of

benzyl In organic chemistry, benzyl is the substituent or molecular fragment possessing the structure . Benzyl features a benzene ring () attached to a methylene group () group. Nomenclature In IUPAC nomenclature, the prefix benzyl refers to a subst ...

ethers:For example, Organic Syntheses, Coll. Vol. 7, p. 386 (1990); Vol. 60, p. 92 (1981). http://orgsynth.org/orgsyn/pdfs/CV7P0386.pdf. For an example of C-N scission, see Organic Syntheses, Coll. Vol. 8, p. 152 (1993); Vol. 68, p. 227 (1990). http://orgsynth.org/orgsyn/pdfs/CV8P0152.pdf :R-OCH2C6H5 + H2 -> R-OH + CH3C6H5 Thioketals undergo hydrogenolysis using Raney nickel in the Mozingo reduction. Laboratory hydrogenolysis is operationally similar to

, 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 a

rubber septum Cannula transfer or cannulation is a set of air-free techniques used with a Schlenk line, in transferring liquid or solution samples between reaction vessels via cannulae, avoiding atmospheric contamination. While the syringes are not the same as ...

. At high pressure, a hydrogenation

autoclave An autoclave is a machine used to carry out industrial and scientific processes requiring elevated temperature and pressure in relation to ambient pressure and/or temperature. Autoclaves are used before surgical procedures to perform steriliza ...

(i.e., a Buchi or Parr

hydrogenator Hydrogenation is a chemical reaction between molecular hydrogen (H2) and another compound or element, usually in the presence of a catalyst such as nickel, palladium or platinum. The process is commonly employed to reduce or saturate organic co ...

) or similar piece of equipment is required.

References

{{Reflist Organic redox reactions Hydrogen