Deoxygenation

{{short description|Chemical reaction removing oxygen atoms from a molecule}} {{redirect|Deoxy|the Pokémon species|Deoxys}}

'''Deoxygenation''' is a chemical reaction involving the removal of oxygen atoms from a molecule. The term also refers to the removal of molecular oxygen (O₂) from gases and solvents, a step in air-free technique and gas purifiers. As applied to organic compounds, deoxygenation is a component of fuels production as well a type of reaction employed in organic synthesis, e.g. of pharmaceuticals.

Compounds with an oxygen atom removed can be described as "desoxy-" or "deoxy-" relative to the original compound, for instance deoxyribose or desoxymescaline.

==Deoxygenation of C-O bonds== ===With replacement by H₂=== The main examples involving the replacement of an oxo group by two hydrogen atoms (A=O → AH₂) are hydrogenolysis. Typical examples use metal catalysts and H₂ as the reagent. Conditions are typically more forcing than hydrogenation.{{cn|date=February 2024}}

Stoichiometric reactions that effect deoxygenation include the Wolff–Kishner reduction for aryl ketones. The replacement of a hydroxyl group by hydrogen (A-OH → A-H) is the point of the Barton–McCombie deoxygenation and the Markó–Lam deoxygenation.{{cn|date=February 2024}}

===Biomass valorization=== Deoxygenation is an important goal of the conversion of biomass to useful fuels and chemicals. Partial deoxygenation is effected by dehydration and decarboxylation.<ref>{{cite journal|title=Green and sustainable manufacture of chemicals from biomass: state of the art|author=Sheldon, Roger A.|journal=Green Chemistry|year=2014|volume=16|issue=3 |pages=950–963|doi=10.1039/C3GC41935E}}</ref>

===Other routes=== Oxygen groups can also be removed by the reductive coupling of ketones, as illustrated by the McMurry reaction. :300px

Epoxides can be deoxygenated using the oxophilic reagent produced by combining tungsten hexachloride and ''n''-butyllithium generates the alkene. This reaction can proceed with loss or retention of configuration.<ref>{{cite journal | title = Deoxygenation of Epoxides with Lower Valent Tungsten Halides: ''trans''-Cyclododecene | author = K. Barry Sharpless, Martha A. Umbreit | journal = Org. Synth. | year = 1981 | volume = 60| page = 29 | doi = 10.15227/orgsyn.060.0029}}</ref><ref><!--placeholder until a secondary source is located-->{{cite journal|title=Stereospecific Deoxygenation of Aliphatic Epoxides to Alkenes under Rhenium Catalysis|author1=Takuya Nakagiri |author2=Masahito Murai |author3=Kazuhiko Takai |journal=Org. Lett.|year=2015|volume=17|issue=13 |pages=3346–3349 |doi=10.1021/acs.orglett.5b01583|pmid=26065934 }}</ref> :thumb|center|220 px|Deoxygenation of ''trans''-cyclododecene oxide, which occurs with retention.

==Deoxygenation of S-O and P-O bonds== ===N=O bonds=== Nitroaromatics are deoxygenated by strongly reducing silyl reagents such as N,N'-bis(trimethylsilyl)-4,4'-bipyridinylidene.<ref>{{cite journal |doi=10.1021/acs.accounts.8b00638|title=Salt-Free Reduction of Transition Metal Complexes by Bis(trimethylsilyl)cyclohexadiene, -dihydropyrazine, and -4,4′-bipyridinylidene Derivatives |year=2019 |last1=Tsurugi |first1=Hayato |last2=Mashima |first2=Kazushi |journal=Accounts of Chemical Research |volume=52 |issue=3 |pages=769–779 |pmid=30794373 |s2cid=73505603 }}</ref>

===P=O bonds=== Phosphorus occurs in nature as oxides, so to produce elemental form of the element, deoxygenation is required. The main method involves carbothermic reduction (i.e., carbon is the deoxygenation agent). :4 Ca₅(PO₄)₃F + 18 SiO₂ + 30 C → 3 P₄ + 30 CO + 18 CaSiO₃ + 2 CaF₂

Oxophilic main group compounds are useful reagents for certain deoxygenations conducted on laboratory scale. The highly oxophilic reagent hexachlorodisilane (Si₂Cl₆) stereospecifically deoxygenates phosphine oxides.<ref>David P. Sebesta "Hexachlorodisilane" in Encyclopedia of Reagents for Organic Synthesis John Wiley, London, 2001. {{doi|10.1002/047084289X.rh007}} Article Online Posting Date: April 15, 2001.</ref><ref>{{cite journal|doi=10.1016/j.tetlet.2018.12.070|title=Reduction of phosphine oxides to phosphines|journal=Tetrahedron Letters|volume=60|issue=8|pages=575–582|year=2019|last1=Podyacheva|first1=Evgeniya|last2=Kuchuk|first2=Ekaterina|last3=Chusov|first3=Denis|s2cid=104364715 }}</ref>

===S=O bonds=== A chemical reagent for the deoxygenation of many sulfur and nitrogen oxo compounds is the combination trifluoroacetic anhydride/sodium iodide.<ref>''Trifluoroacetic anhydride-sodium iodide reagent. Nature and applications'' Arkivoc '''2007''' (JE-2136MR) Zbigniew H. Kudzin, Marcin H. Kudzin, Józef Drabowicz, and Andrzej Kotyński [http://content.arkat-usa.org/ARKIVOC/JOURNAL_CONTENT/manuscripts/2007/JE-2136MR%20as%20published%20mainmanuscript.pdf Link]</ref> For example, in the deoxygenation of the sulfoxide ''diphenylsulfoxide'' to the sulfide ''diphenylsulfide'':

:400px|Sulfoxide deoxygenation

The reaction mechanism is based on the activation of the sulfoxide by a trifluoroacetyl group and oxidation of iodine. Iodine is formed quantitatively in this reaction and therefore the reagent is used for the analytical detection of many oxo compounds. :400px|TFAA NaI deoxygenation mechanism

== See also == * Degassing * Preparation of stable carbenes * Ocean deoxygenation * Oxophilicity

==References== {{Reflist}}

Category:Organic redox reactions Category:Gas technologies