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 breaking ...

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 molecula ...

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 b ...

(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-to ...

.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 organic ...

, 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 Paul Sabatier may refer to: *Paul Sabatier (chemist) (1854–1941), French chemist and Nobel Prize winner *Paul Sabatier (theologian) (1858–1928), French clergyman and historian See also *Paul Sabatier University Paul Sabatier University (''U ...

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 liquid w ...

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 unstable ...

Homer Burton Adkins Homer Burton Adkins (16 January 1892 – 10 August 1949) was an American chemist who studied the hydrogenation of organic compounds. Adkins was regarded as top in his field and a world authority on the hydrogenation of organic compounds. Adk ...

and

Ralph Connor Ralph (pronounced ; or ,) is a male given name of English, Scottish and Irish origin, derived from the Old English ''Rædwulf'' and Radulf, cognate with the Old Norse ''Raðulfr'' (''rað'' "counsel" and ''ulfr'' "wolf"). The most common forms ...

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 under ...

(H₂S). The hydrogen sulfide is subsequently recovered in an amine treater 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 The Claus process is the most significant gas desulfurizing process, recovering elemental sulfur from gaseous hydrogen sulfide. First patented in 1883 by the chemist Carl Friedrich Claus, the Claus process has become the industry standard. Th ...

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 Copper chromite is an inorganic compound with the formula Cu2Cr2O5. It is a black solid that is used to catalyze reactions in organic synthesis. History The material was first described in 1908. The catalyst was developed in North America by Home ...

. 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 + 2 H2 ...

reaction used in the

Neste Renewable Diesel Neste Renewable Diesel (formerly NExBTL) is a vegetable oil refining fuel production process commercialized by the Finnish oil and refining company Neste. Whether as an admixture or in its pure form, Neste Renewable Diesel is able to supplement or ...

process, the vegetable oil refining 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, an alkane, or paraffin (a historical trivial name that also has other meanings), is an acyclic saturated hydrocarbon. In other words, an alkane consists of hydrogen and carbon atoms arranged in a tree structure in wh ...

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 substi ...

ethers:For example,

Organic Syntheses ''Organic Syntheses'' is a peer-reviewed scientific journal that was established in 1921. It publishes detailed and checked procedures for the synthesis of organic compounds. A unique feature of the review process is that all of the data and exp ...

, 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

, Coll. Vol. 8, p. 152 (1993); Vol. 68, p. 227 (1990). http://orgsynth.org/orgsyn/pdfs/CV8P0152.pdf :R-OCH2C6H5 + H2 -> R-OH + CH3C6H5

Thioketal In organosulfur chemistry, a thioketal is the sulfur analogue of a ketal (), with one of the oxygen replaced by sulfur (as implied by the ''thio-'' prefix), giving the structure . A dithioketal has ''both'' oxygens replaced by sulfur (). Thio ...

s undergo hydrogenolysis using Raney nickel in the

Mozingo reduction The Mozingo reduction, also known as Mozingo reaction or thioketal reduction, is a chemical reaction capable of fully reducing a ketone or aldehyde to the corresponding alkane via a dithioacetal. The reaction scheme is as follows: The ketone o ...

. 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. 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 sterilizati ...

(i.e., a Buchi or Parr hydrogenator) or similar piece of equipment is required.

References

{{Reflist Organic redox reactions Hydrogen