Hydrogenolysis
Encyclopedia
Hydrogenolysis is a chemical reaction
whereby 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. A related reaction is hydrogenation
, where hydrogen is added to the molecule, without cleaving bonds. Usually hydrogenolysis is conducted catalytically using hydrogen gas.
in reference to hydrogenolysis of carbon–carbon bonds. Earlier, Sabatier
had already observed the hydrogenolysis of benzyl alcohol to toluene, and as early as 1906, Padoa and Ponti had observed the hydrogenolysis of furfuryl alcohol
. Adkins and Connors were the first to call the carbon–oxygen bond cleavage "hydrogenolysis".
, catalytic hydrogenolysis of feedstocks is conducted on a large scale to remove sulfur from feedstocks, releasing gaseous hydrogen sulfide
(H2S). The 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). 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.
. Debenzylation is most common and involves the cleavage of benzyl
ethers:
Thioketal
s undergo hydrogenolysis using Raney nickel
.
Laboratory hydrogenolysis is operationally similar to hydrogenation
, 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
(i.e., a Parr hydrogenator) or similar piece of equipment is required.
Chemical reaction
A chemical reaction is a process that leads to the transformation of one set of chemical substances to another. Chemical reactions can be either spontaneous, requiring no input of energy, or non-spontaneous, typically following the input of some type of energy, such as heat, light or electricity...
whereby a carbon–carbon or carbon–heteroatom
Heteroatom
In organic chemistry, a heteroatom is any atom that is not carbon or hydrogen. Usually, the term is used to indicate that non-carbon atoms have replaced carbon in the backbone of the molecular structure...
single bond is cleaved or undergoes "lysis" by hydrogen. The heteroatom may vary, but it usually is oxygen, nitrogen, or sulfur. A related reaction is hydrogenation
Hydrogenation
Hydrogenation, to treat with hydrogen, also a form of chemical reduction, is a chemical reaction between molecular hydrogen and another compound or element, usually in the presence of a catalyst. The process is commonly employed to reduce or saturate organic compounds. Hydrogenation typically...
, 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 EllisCarleton Ellis
Carleton Ellis was an American inventor and a pioneer in the field of organic chemistry. He is the forgotten father of margarine, polyester, anti-knock gasoline, paint and varnish remover, and holder of 753 patents. A native of Keene, New Hampshire, he was the valedictorian of his high school...
in reference to hydrogenolysis of carbon–carbon bonds. Earlier, Sabatier
Paul Sabatier (chemist)
Paul Sabatier FRS was a French chemist, born at Carcassonne. He taught science classes most of his life before he became Dean of the Faculty of Science at the University of Toulouse in 1905....
had already observed the hydrogenolysis of benzyl alcohol to toluene, and as early as 1906, Padoa and Ponti had observed the hydrogenolysis of furfuryl alcohol
Furfuryl alcohol
Furfuryl alcohol, also called 2-furylmethanol or 2-furancarbinol, is an organic compound containing a furan substituted with a hydroxymethyl group. It is a clear colorless liquid when pure, but becomes amber colored upon prolonged standing. It possesses a faint burning odor and a bitter taste. ...
. Adkins and Connors were the first to call the carbon–oxygen bond cleavage "hydrogenolysis".
In the petrochemical industry
In petroleum refineriesOil refinery
An oil refinery or petroleum refinery is an industrial process plant where crude oil is processed and refined into more useful petroleum products, such as gasoline, diesel fuel, asphalt base, heating oil, kerosene, and liquefied petroleum gas...
, catalytic hydrogenolysis of feedstocks is conducted on a large scale to remove sulfur from feedstocks, releasing gaseous hydrogen sulfide
Hydrogen sulfide
Hydrogen sulfide is the chemical compound with the formula . It is a colorless, very poisonous, flammable gas with the characteristic foul odor of expired eggs perceptible at concentrations as low as 0.00047 parts per million...
(H2S). The hydrogen sulfide is subsequently recovered in an amine treater and finally converted to elemental sulfur
Sulfur
Sulfur or sulphur is the chemical element with atomic number 16. In the periodic table it is represented by the symbol S. It is an abundant, multivalent non-metal. Under normal conditions, sulfur atoms form cyclic octatomic molecules with chemical formula S8. Elemental sulfur is a bright yellow...
in a Claus process
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 scientist Carl Friedrich Claus, the Claus process has become the industry standard....
unit. In those industries, desulfurization process units are often referred to as hydrodesulfurizers
Hydrodesulfurization
Hydrodesulfurization is a catalytic chemical process widely used to remove sulfur from natural gas and from refined petroleum products such as gasoline or petrol, jet fuel, kerosene, diesel fuel, and fuel oils...
(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.
In the laboratory
In the laboratory, hydrogenolysis is used in organic synthesisOrganic synthesis
Organic synthesis is a special branch of chemical synthesis and is concerned with the construction of organic compounds via organic reactions. Organic molecules can often contain a higher level of complexity compared to purely inorganic compounds, so the synthesis of organic compounds has...
. Debenzylation is most common and involves the cleavage of benzyl
Benzyl
In organic chemistry, benzyl is the term used to describe the substituent or molecular fragment possessing the structure C6H5CH2-. Benzyl features a benzene ring attached to a CH2 group.-Nomenclature:...
ethers:
- ROCH2C6H5 + H2 → ROH + CH3C6H5
Thioketal
Thioketal
In chemistry, a thioketal is the sulfur analogue of a ketal, with one of the oxygen replaced by sulfur. A dithioketal has both oxygens replaced by sulfur.Thioketals can be obtained by reacting ketones or aldehydes with thioles....
s undergo hydrogenolysis using Raney nickel
Raney nickel
Raney nickel is a solid catalyst composed of fine grains of a nickel-aluminium alloy, used in many industrial processes. It was developed in 1926 by American]] engineer Murray Raney as an alternative catalyst for the hydrogenation of vegetable oils in industrial processes...
.
Laboratory hydrogenolysis is operationally similar to hydrogenation
Hydrogenation
Hydrogenation, to treat with hydrogen, also a form of chemical reduction, is a chemical reaction between molecular hydrogen and another compound or element, usually in the presence of a catalyst. The process is commonly employed to reduce or saturate organic compounds. Hydrogenation typically...
, 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
Autoclave
An autoclave is an instrument used to sterilize equipment and supplies by subjecting them to high pressure saturated steam at 121 °C for around 15–20 minutes depending on the size of the load and the contents. It was invented by Charles Chamberland in 1879, although a precursor known as the...
(i.e., a Parr hydrogenator) or similar piece of equipment is required.