Editing Carbon monoxide (section)

== Chemistry ==
Carbon monoxide has a wide range of functions across all disciplines of chemistry. The four premier categories of reactivity involve [[Metal carbonyl|metal-carbonyl]] catalysis, [[Radical (chemistry)|radical]] chemistry, [[cation]] and [[anion]] chemistries.<ref>{{Cite journal|date=2019-03-14|title=The Chemistry of CO: Carbonylation|journal=Chem|language=en|volume=5|issue=3|pages=526–552|doi=10.1016/j.chempr.2018.11.006|issn=2451-9294|doi-access=free|last1=Peng|first1=Jin-Bao|last2=Geng|first2=Hui-Qing|last3=Wu|first3=Xiao-Feng|bibcode=2019Chem....5..526P }}</ref>

===Coordination chemistry===
{{Main|Metal carbonyl}}

[[File:MO COeng.svg|class=skin-invert-image|thumb|left|200px|Energy level scheme of the σ and π orbitals of carbon monoxide]]
[[Image:Carbon-monoxide-HOMO-phase-3D-balls.svg|thumb|right|150px|The [[HOMO/LUMO|HOMO]] of CO is a σ [[molecular orbital|MO]].]]
[[Image:Carbon-monoxide-LUMO-phase-3D-balls.png|thumb|right|150px|The [[HOMO/LUMO|LUMO]] of CO is a π* [[antibonding]] [[molecular orbital|MO]].]]

Most metals form [[coordination complex]]es containing covalently attached carbon monoxide. These derivatives, which are called [[metal carbonyls]], tend to be more robust when the metal is in lower oxidation states. For example [[iron pentacarbonyl]] ({{chem2|Fe(CO)5}}) is an air-stable, distillable liquid. [[Nickel carbonyl]] is a [[metal carbonyl complex]] that forms by the direct combination of carbon monoxide with the metal:<ref>{{cite book|title=Organometallics|author=C. Elschenbroich|publisher=VCH|year=2006|isbn=  978-3-527-29390-2}}</ref>
:{{chem2|Ni + 4 CO -> Ni(CO)4}} (1 [[Bar (unit)|bar]], 55 °C)
These volatile complexes are often highly toxic.  Some metal–CO complexes are prepared by decarbonylation of organic solvents, not from CO. For instance, [[iridium(III) chloride|iridium trichloride]] and [[triphenylphosphine]] react in boiling [[2-Methoxyethanol|2-methoxyethanol]] or [[dimethylformamide|DMF]] to afford {{chem2|IrCl(CO)(PPh3)2|link=Vaska's complex}}.

As a ligand, CO binds through carbon, forming a kind of triple bond. The lone pair on the carbon atom donates electron density to form a M-CO [[sigma bond]]. The two π* orbitals on CO bind to filled metal orbitals.  The effect is related to the [[Dewar-Chatt-Duncanson model]]. The effects of the quasi-triple M-C bond is reflected in the [[infrared spectrum]] of these complexes. Whereas free CO vibrates at 2143&nbsp;cm<sup>−1</sup>, its complexes tend to absorb near 1950&nbsp;cm<sup>−1</sup>.

[[Image:IronPentacarbonylStructure.png|class=skin-invert-image|150px|Structure of iron pentacarbonyl.]]

===Organic and main group chemistry===
{{Main|Carbonylation}}

In the presence of strong acids,  [[alkene]]s react with [[carboxylic acids]].  Hydrolysis of this species (an [[acylium ion]]) gives the carboxylic acid,  a net process known as the [[Koch–Haaf reaction]].<ref name="koch">{{cite journal |doi=10.15227/orgsyn.044.0001 |title=1-Adamantanecarboxylic Acid |journal=Organic Syntheses |date=1964 |volume=44 |page=1|first1=H.|last1=Koch|first2=W.|last2=Haaf }}</ref> In the [[Gattermann–Koch reaction]], [[Aromatic hydrocarbon|arenes]] are converted to [[benzaldehyde]] derivatives in the presence of CO, {{chem2|AlCl3|link=aluminium chloride}}, and [[hydrogen chloride|HCl]].<ref name="coleman">{{OrgSynth|title=''p''-Tolualdehyde|author=Coleman, G. H.|author2=Craig, David|volume=12|pages=80|year=1932|doi=10.15227/orgsyn.012.0080}}</ref>

A mixture of hydrogen gas and CO reacts with [[alkene]]s to give aldehydes.  The process requires the presence of metal catalysts.<ref>Chatani, N.; Murai, S. "Carbon Monoxide" in Encyclopedia of Reagents for Organic Synthesis (Ed: L. Paquette) 2004, J. Wiley & Sons, New York. {{doi|10.1002/047084289X}}</ref>

With main group reagents, CO undergoes several noteworthy reactions. [[halogenation|Chlorination]] of CO is the industrial route to the important compound [[phosgene]]. With [[borane]] CO forms the adduct {{chem2|H3BCO|link=Borane carbonyl}}, which is [[isoelectronic]] with the [[acylium]] cation {{chem2|[H3CCO]+}}. CO reacts with [[sodium]] to give products resulting from C−C coupling such as [[acetylenediol|sodium acetylenediolate]] {{chem2|2Na+*C2O2(2-)}}. It reacts with molten [[potassium]] to give a mixture of an organometallic compound, [[acetylenediol|potassium acetylenediolate]] {{chem2|2K+*C2O2(2-)}}, [[benzenehexol|potassium benzenehexolate]] {{chem2|6K+*C6O6(6-)}},<ref name="wbuechIV">{{cite journal|last1=Büchner|first1=W.|last2=Weiss|first2=E.|year=1964|title=Zur Kenntnis der sogenannten "Alkalicarbonyle" IV[1] Über die Reaktion von geschmolzenem Kalium mit Kohlenmonoxid|journal=Helvetica Chimica Acta|volume=47|issue=6|pages=1415–1423|doi=10.1002/hlca.19640470604}}
</ref> and [[rhodizonic acid|potassium rhodizonate]] {{chem2|2K+*C6O6(2-)}}.<ref>{{Cite book|author=Fownes, George|url=https://archive.org/details/amanualelementa02fowngoog|title=A Manual of elementary chemistry|publisher=H.C. Lea|year=1869|page=[https://archive.org/details/amanualelementa02fowngoog/page/n682 678]}}</ref>

The compounds [[cyclohexanehexone]] or triquinoyl ({{chem2|C6O6}}) and [[cyclopentanepentone]] or leuconic acid ({{chem2|C5O5}}), which so far have been obtained only in trace amounts, can be regarded as polymers of carbon monoxide. At pressures exceeding 5 [[pascal (unit)|GPa]], carbon monoxide converts to [[polycarbonyl]], a solid polymer that is metastable at atmospheric pressure but is explosive.<ref>{{Cite journal|last1=Katz|first1=Allen I.|last2=Schiferl|first2=David|last3=Mills|first3=Robert L.|year=1984|title=New phases and chemical reactions in solid carbon monoxide under pressure|journal=The Journal of Physical Chemistry|volume=88|issue=15|pages=3176–3179|doi=10.1021/j150659a007}}</ref><ref>{{Cite journal|last1=Evans|first1=W. J.|last2=Lipp|first2=M. J.|last3=Yoo|first3=C.-S.|last4=Cynn|first4=H.|last5=Herberg|first5=J. L.|last6=Maxwell|first6=R. S.|last7=Nicol|first7=M. F.|year=2006|title=Pressure-Induced Polymerization of Carbon Monoxide: Disproportionation and Synthesis of an Energetic Lactonic Polymer|url=https://digital.library.unt.edu/ark:/67531/metadc892676/|journal=Chemistry of Materials|volume=18|issue=10|pages=2520–2531|doi=10.1021/cm0524446}}</ref>

==== Laboratory preparation ====
Carbon monoxide is conveniently produced in the laboratory by the [[Dehydration reaction|dehydration]] of [[formic acid]] or [[oxalic acid]], for example with concentrated [[sulfuric acid]].<ref name="koch" /><ref name="coleman" /><ref name="Georg">{{cite book|last=Brauer|first=Georg|url=https://books.google.com/books?id=TLYatwAACAAJ&q=Handbook+of+Preparative+Inorganic+Chemistry|title=Handbook of Preparative Inorganic Chemistry Vol. 1, 2nd Ed|date=1963|publisher=Academic Press|isbn=978-0121266011|location=New York|page=646}}</ref> Another method is heating an intimate mixture of powdered [[zinc]] metal and [[calcium carbonate]], which releases CO and leaves behind [[zinc oxide]] and [[calcium oxide]]:
:{{chem2|Zn + CaCO3 -> ZnO + CaO + CO}}

[[Silver nitrate]] and [[iodoform]] also afford carbon monoxide:
:{{chem2|CHI3 + 3 AgNO3 + H2O -> 3 HNO3 + CO + 3 AgI}}

Finally, metal [[oxalate]] salts release CO upon heating, leaving a [[carbonate]] as byproduct:
:{{chem2|Na2C2O4 -> Na2CO3 + CO}}