Physics:Deoxygenation
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.[citation needed]
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.[citation needed]
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.[1]
Other routes
Oxygen groups can also be removed by the reductive coupling of ketones, as illustrated by the McMurry reaction.
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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.[2][3]
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.[4]
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.[5][6]
S=O bonds
A chemical reagent for the deoxygenation of many sulfur and nitrogen oxo compounds is the combination trifluoroacetic anhydride/sodium iodide.[7] For example, in the deoxygenation of the sulfoxide diphenylsulfoxide to the sulfide diphenylsulfide:
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.
See also
- Degassing
- Preparation of stable carbenes
- Ocean deoxygenation
- Oxophilicity
References
- ↑ Sheldon, Roger A. (2014). "Green and sustainable manufacture of chemicals from biomass: state of the art". Green Chemistry 16 (3): 950–963. doi:10.1039/C3GC41935E.
- ↑ K. Barry Sharpless, Martha A. Umbreit (1981). "Deoxygenation of Epoxides with Lower Valent Tungsten Halides: trans-Cyclododecene". Org. Synth. 60: 29. doi:10.15227/orgsyn.060.0029.
- ↑ Takuya Nakagiri; Masahito Murai; Kazuhiko Takai (2015). "Stereospecific Deoxygenation of Aliphatic Epoxides to Alkenes under Rhenium Catalysis". Org. Lett. 17 (13): 3346–3349. doi:10.1021/acs.orglett.5b01583. PMID 26065934.
- ↑ Tsurugi, Hayato; Mashima, Kazushi (2019). "Salt-Free Reduction of Transition Metal Complexes by Bis(trimethylsilyl)cyclohexadiene, -dihydropyrazine, and -4,4′-bipyridinylidene Derivatives". Accounts of Chemical Research 52 (3): 769–779. doi:10.1021/acs.accounts.8b00638. PMID 30794373.
- ↑ 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.
- ↑ Podyacheva, Evgeniya; Kuchuk, Ekaterina; Chusov, Denis (2019). "Reduction of phosphine oxides to phosphines". Tetrahedron Letters 60 (8): 575–582. doi:10.1016/j.tetlet.2018.12.070.
- ↑ Trifluoroacetic anhydride-sodium iodide reagent. Nature and applications Arkivoc 2007 (JE-2136MR) Zbigniew H. Kudzin, Marcin H. Kudzin, Józef Drabowicz, and Andrzej Kotyński Link
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