:Oxidative coupling
Oxidative coupling in chemistry is a coupling reaction of two molecular entities through an oxidative process. Usually oxidative couplings are catalysed by a transition metal complex like in classical cross-coupling reactions, although the underlying mechanism is different due to the oxidation process that requires an external (or internal) oxidant.Oxidative Cross-Coupling Reactions. Aiwen Lei, Wei Shi, Chao Liu, Wei Liu, Hua Zhang, Chuan He, Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim, Germany (2017). {{doi|10.1002/9783527680986}}{{cite journal|title=Oxidative Coupling Mechanisms: Current State of Understanding|author=Ignacio Funes-Ardoiz |author2=Feliu Maseras |journal=ACS Catalysis|year=2018|volume=8|issue=2 |pages=1161–1172|doi=10.1021/acscatal.7b02974|doi-access=free}} Many such couplings utilize dioxygen as the stoichiometric oxidant but proceed by electron transfer.IUPAC. Compendium of Chemical Terminology, 2nd ed. (the "Gold Book"). Compiled by A. D. McNaught and A. Wilkinson. Blackwell Scientific Publications, Oxford (1997). {{doi|10.1351/goldbook}}
C-C Couplings
Many oxidative couplings generate new C-C bonds. Early examples involve coupling of terminal alkynes:{{cite journal|title=Copper-Catalyzed Aerobic Oxidative C-H Functionalizations: Trends and Mechanistic Insights|author=Alison E. Wendlandt |author2=Alison M. Suess |author3=Shannon S. Stahl |journal=Angew. Chem. Int. Ed.|year=2011|volume=50|issue=47 |pages=11062–11087|doi=10.1002/anie.201103945|pmid=22034061 }}
:2 RC≡CH + 2 Cu(I) → RC≡C-C≡CR + 2 Cu + 2 H+
=Aromatic coupling=
Image:Lignin structure.svg structure; aryl-aryl linkages arise from enzymatic oxidative couplings.{{cite encyclopedia |last=Lebo |first=Stuart E. Jr. |author2=Gargulak, Jerry D. |author3=McNally, Timothy J. |encyclopedia=Kirk‑Othmer Encyclopedia of Chemical Technology |chapter-url= http://www.mrw.interscience.wiley.com/emrw/9780471238966/kirk/article/lignlin.a01/current/pdf |access-date=2007-10-14 |year=2001 |publisher= John Wiley & Sons, Inc |doi=10.1002/0471238961.12090714120914.a01.pub2
|chapter=Lignin |title=Kirk-Othmer Encyclopedia of Chemical Technology |isbn=0-471-23896-1 }}]]
In oxidative aromatic coupling the reactants are electron-rich aromatic compounds. Typical substrates are phenols and typical catalysts are copper and iron compounds and enzymes,Grzybowski, M., Skonieczny, K., Butenschön, H. and Gryko, D. T. (2013), Comparison of Oxidative Aromatic Coupling and the Scholl Reaction Angew. Chem. Int. Ed., 52: 9900–9930. {{doi|10.1002/anie.201210238}} although Scholl demonstrated that high heat and a Lewis acid suffice. The first reported synthetic application dates back to 1868 with Julius Löwe and the synthesis of ellagic acid by heating gallic acid with arsenic acid or silver oxide.Löwe, Zeitschrift für Chemie, 1868, 4, 603 Another reaction is the synthesis of 1,1'-Bi-2-naphthol from 2-naphthol by iron chloride, discovered in 1873 by Alexander DianinA. P. Dianin, Zh. Russ. Fiz.-Khim. O-va. 1874 , 183 (S)-BINOL can be prepared directly from an asymmetric oxidative coupling of 2-naphthol with copper(II) chloride.{{cite journal|last1 = Brussee|first1 = J.|last2 = Jansen|first2 = A. C. A.|year = 1983|title = A highly stereoselective synthesis of S-(−)-[1,1′-binaphthalene]-2,2′-diol|journal = Tetrahedron Letters|volume = 24|issue = 31|pages = 3261–3262|doi = 10.1016/S0040-4039(00)88151-4}}
=Coupling of methane=
Coupling reactions involving methane are highly sought, related to C1 chemistry because C2 derivatives are far more valuable than methane. The oxidative coupling of methane gives ethylene:{{cite journal| author=Zhang, Q. |year = 2003| title = Recent Progress in Direct Partial Oxidation of Methane to Methanol | journal =J. Natural Gas Chem.| volume = 12|pages = 81–89}}Olah, G., Molnar, A. "Hydrocarbon Chemistry" John Wiley & Sons, New York, 2003. {{ISBN|978-0-471-41782-8}}.
: 2{{chem|CH|4}} + {{chem|O|2}} → {{chem|C|2|H|4}} + 2{{chem|H|2|O}}
Other oxidative couplings
File:Electrolysis of Water.png
The oxygen evolution reaction entails, in effect, the oxidative coupling of water molecules to give O2.
References
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