Carbon monoxide (chemical formulaCO) is a poisonous, flammable gas that is colorless, odorless, tasteless, and slightly less dense than air. Carbon monoxide consists of onecarbon atom and oneoxygen atom connected by atriple bond. It is the simplestcarbon oxide. Incoordination complexes, the carbon monoxideligand is calledcarbonyl. It is a key ingredient in many processes in industrial chemistry.[5]
The most common source of carbon monoxide is the partialcombustion of carbon-containing compounds. Numerous environmental and biological sources generate carbon monoxide. In industry, carbon monoxide is important in the production of many compounds, including drugs, fragrances, and fuels.[6]
Indoors CO is one of the most acutely toxic contaminants affectingindoor air quality. CO may be emitted from tobacco smoke and generated from malfunctioning fuel-burning stoves (wood, kerosene, natural gas, propane) and fuel-burning heating systems (wood, oil, natural gas) and from blockedflues connected to these appliances.[7]Carbon monoxide poisoning is the most common type of fatal air poisoning in many countries.[8][7][9]
Carbon monoxide has important biological roles across phylogenetic kingdoms. It is produced by many organisms, including humans. In mammalian physiology, carbon monoxide is a classical example ofhormesis where low concentrations serve as an endogenousneurotransmitter (gasotransmitter) and high concentrations aretoxic, resulting incarbon monoxide poisoning. It isisoelectronic with bothcyanide anionCN− and molecularnitrogenN2.
The carbon and oxygen are connected by atriple bond that consists of a net twopi bonds and onesigma bond. Thebond length between the carbon atom and the oxygen atom is 112.8 pm.[10][11] This bond length is consistent with a triple bond, as in molecular nitrogen (N2), which has a similar bond length (109.76 pm) and nearly the samemolecular mass. Carbon–oxygen double bonds are significantly longer, 120.8 pm informaldehyde, for example.[12] The boiling point (82 K) and melting point (68 K) are very similar to those ofN2 (77 K and 63 K, respectively). Thebond-dissociation energy of 1072 kJ/mol is stronger than that ofN2 (942 kJ/mol) and represents the strongest chemical bond known.[13]
The strength of theC≡O bond in carbon monoxide is indicated by the high frequency of its vibration, 2143 cm−1.[17] For comparison, organic carbonyls such as ketones and esters absorb at around 1700 cm−1.
Carbon and oxygen together have a total of 10electrons in thevalence shell. Following theoctet rule for both carbon and oxygen, the two atoms form atriple bond, with six shared electrons in three bonding molecular orbitals, rather than the usual double bond found in organic carbonyl compounds. Since four of the shared electrons come from the oxygen atom and only two from carbon, one bonding orbital is occupied by two electrons from oxygen, forming a dative ordipolar bond. This causes a C←Opolarization of the molecule, with a small negative charge on carbon and a small positive charge on oxygen. The other two bonding orbitals are each occupied by one electron from carbon and one from oxygen, forming (polar) covalent bonds with a reverse C→O polarization since oxygen is moreelectronegative than carbon. In the free carbon monoxide molecule, a net negative charge δ− remains at the carbon end and the molecule has a smalldipole moment of 0.122 D.[18]
The molecule is therefore asymmetric: oxygen is more electron dense than carbon and is also slightly positively charged compared to carbon being negative.
The most important resonance form of carbon monoxide is−C≡O+. An important minor resonance contributor is the non-octet carbenic structure :C=O.
Carbon monoxide has a computed fractional bond order of 2.6, indicating that the "third" bond is important but constitutes somewhat less than a full bond.[19] Thus, in valence bond terms,−C≡O+ is the most important structure, while :C=O is non-octet, but has a neutral formal charge on each atom and represents the second most important resonance contributor. Because of the lone pair and divalence of carbon in this resonance structure, carbon monoxide is often considered to be an extraordinarily stabilizedcarbene.[20]Isocyanides are compounds in which the O is replaced by an NR (R = alkyl or aryl) group and have a similar bonding scheme.
If carbon monoxide acts as aligand, the polarity of the dipole may reverse with a net negative charge on the oxygen end, depending on the structure of thecoordination complex.[21]See also the section"Coordination chemistry" below.
Theoretical and experimental studies show that, despite the greater electronegativity of oxygen, the dipole moment points from the more-negative carbon end to the more-positive oxygen end.[22][23] The three bonds are in factpolar covalent bonds that are strongly polarized. The calculated polarization toward the oxygen atom is 71% for theσ-bond and 77% for bothπ-bonds.[24]
Theoxidation state of carbon in carbon monoxide is +2 in each of these structures. It is calculated by counting all the bonding electrons as belonging to the more electronegative oxygen. Only the two non-bonding electrons on carbon are assigned to carbon. In this count, carbon then has only two valence electrons in the molecule compared to four in the free atom.
Monthly averages of global concentrations of tropospheric carbon monoxide at an altitude of about 12,000 feet. Data were collected by the MOPITT (Measurements Of Pollution In The Troposphere) sensor on NASA's Terra satellite.[25]
Carbon monoxide occurs in many environments, usually in trace levels. Photochemical degradation of plant matter, for example, generates an estimated 60 million tons/year.[26] Typical concentrations inparts per million are as follows:
The streak of red, orange, and yellow acrossSouth America,Africa, and theAtlantic Ocean in this animation points to high levels of carbon monoxide on September 30, 2005.Carbon monoxide concentrations in Northern Hemisphere spring as measured with the MOPITT instrument
Carbon monoxide (CO) is present in small amounts (about 80ppb) in theEarth's atmosphere. Most comes from chemical reactions withorganic compounds emitted by human activities and natural origins due tophotochemical reactions in thetroposphere that generate about 5 × 1012 kilograms per year.[34] Other natural sources of CO include volcanoes,forest andbushfires, and other miscellaneous forms of combustion such asfossil fuels.[35] Small amounts are also emitted from the ocean, and from geological activity because carbon monoxide occurs dissolved in molten volcanic rock at high pressures in the Earth'smantle.[36] Because natural sources of carbon monoxide vary from year to year, it is difficult to accurately measure natural emissions of the gas.
Carbon monoxide has an indirect effect onradiative forcing by elevating concentrations of directgreenhouse gases, includingmethane andtroposphericozone. CO can react chemically with other atmospheric constituents (primarily thehydroxylradical,•OH) that would otherwise destroy methane.[37] Through natural processes in the atmosphere, it is oxidized tocarbon dioxide and ozone. Carbon monoxide is short-lived in the atmosphere (with an average lifetime of about one to two months), and spatially variable in concentration.[38]
Due to its long lifetime in the mid-troposphere, carbon monoxide is also used as a tracer for pollutant plumes.[39]
Beyond Earth, carbon monoxide is the second-most common diatomic molecule in theinterstellar medium, aftermolecular hydrogen. Because of its asymmetry, thispolar molecule produces far brighterspectral lines than the hydrogen molecule, making CO much easier to detect. Interstellar CO was first detected withradio telescopes in 1970. It is now the most commonly used tracer of molecular gas in general in the interstellar medium of galaxies, as molecular hydrogen can only be detected using ultraviolet light, which requiresspace telescopes. Carbon monoxide observations provide much of the information about themolecular clouds in which moststars form.[40][41]
Beta Pictoris, the second brightest star in the constellationPictor, shows anexcess of infrared emission compared to normal stars of its type, which is caused by large quantities of dust and gas (including carbon monoxide)[42][43] near the star.
In theatmosphere of Venus carbon monoxide occurs as a result of the photodissociation of carbon dioxide by electromagnetic radiation of wavelengths shorter than 169nm. It has also been identified spectroscopically on the surface of Neptune's moonTriton.[44]
Solid carbon monoxide is a component ofcomets.[45] Thevolatile or "ice" component ofHalley's Comet is about 15% CO.[46] At room temperature and at atmospheric pressure, carbon monoxide is actually only metastable (seeBoudouard reaction) and the same is true at low temperatures where CO andCO2 are solid, but nevertheless it can exist for billions of years in comets. There is very little CO in the atmosphere ofPluto, which seems to have been formed from comets. This may be because there is (or was) liquid water inside Pluto.
Carbon monoxide can react with water to form carbon dioxide and hydrogen:
CO + H2O → H2 + CO2
This is called thewater-gas shift reaction when occurring in the gas phase, but it can also take place (very slowly) in an aqueous solution.If the hydrogen partial pressure is high enough (for instance in an underground sea),formic acid will be formed:
CO + H2O → HCOOH
These reactions can take place in a few million years even at temperatures such as found on Pluto.[47]
Carbon monoxide is a temporary atmospheric pollutant in some urban areas, chiefly from the exhaust ofinternal combustion engines (including vehicles, portable and back-up generators, lawnmowers, power washers, etc.), but also from incomplete combustion of various other fuels (including wood, coal, charcoal, oil, paraffin, propane, natural gas, and trash).
Large CO pollution events can be observed from space over cities.[48]
Carbon monoxide is, along withaldehydes, part of the series of cycles of chemical reactions that formphotochemical smog. It reacts with hydroxyl radical (•OH) to produce a radical intermediate•HOCO, which rapidly transfers its radical hydrogen toO2 to formperoxy radical (HO2•) and carbon dioxide (CO2).[49] Peroxy radical subsequently reacts withnitrogen oxide (NO) to formnitrogen dioxide (NO2) and hydroxyl radical.NO2 gives O(3P) via photolysis, thereby formingO3 following reaction withO2.Since hydroxyl radical is formed during the formation ofNO2, the balance of the sequence of chemical reactions starting with carbon monoxide and leading to the formation of ozone is:
CO + 2 O2 + hν → CO2 + O3
(where hν refers to thephoton of light absorbed by theNO2 molecule in the sequence)
Although the creation ofNO2 is the critical step leading to low levelozone formation, it also increases this ozone in another, somewhat mutually exclusive way, by reducing the quantity of NO that is available to react with ozone.[50]
Carbon monoxide is one of the most acutely toxicindoor air contaminants. Carbon monoxide may be emitted from tobacco smoke and generated from malfunctioning fuel burning stoves (wood, kerosene, natural gas, propane) and fuel burning heating systems (wood, oil, natural gas) and from blockedflues connected to these appliances.[7] Indeveloped countries the main sources of indoor CO emission come from cooking and heating devices that burnfossil fuels and are faulty, incorrectly installed or poorly maintained.[51] Appliance malfunction may be due to faulty installation or lack of maintenance and proper use.[7] Inlow- and middle-income countries the most common sources of CO in homes are burningbiomass fuels and cigarette smoke.[51]
Miners refer to carbon monoxide as "whitedamp" or the "silent killer". It can be found in confined areas of poor ventilation in both surface mines and underground mines. The most common sources of carbon monoxide in mining operations are the internal combustion engine and explosives; however, in coal mines, carbon monoxide can also be found due to the low-temperature oxidation of coal.[52] The idiom "Canary in the coal mine" pertained to an early warning of a carbon monoxide presence.[53]
Carbon monoxide poisoning is the most common type of fatal air poisoning in many countries. Acute exposure can also lead to long-term neurological effects such as cognitive and behavioural changes. Severe CO poisoning may lead to unconsciousness, coma and death. Chronic exposure to low concentrations of carbon monoxide may lead to lethargy, headaches, nausea, flu-like symptoms and neuropsychological and cardiovascular issues.[8][7][9]
Carbon monoxide has a wide range of functions across all disciplines of chemistry. The four premier categories of reactivity involvemetal-carbonyl catalysis,radical chemistry,cation andanion chemistries.[54]
Energy level scheme of the σ and π orbitals of carbon monoxideTheHOMO of CO is a σMO.TheLUMO of CO is a π*antibondingMO.
Most metals formcoordination complexes containing covalently attached carbon monoxide. These derivatives, which are calledmetal carbonyls, tend to be more robust when the metal is in lower oxidation states. For exampleiron pentacarbonyl (Fe(CO)5) is an air-stable, distillable liquid.Nickel carbonyl is ametal carbonyl complex that forms by the direct combination of carbon monoxide with the metal:[55]
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-COsigma bond. The two π* orbitals on CO bind to filled metal orbitals. The effect is related to theDewar-Chatt-Duncanson model. The effects of the quasi-triple M-C bond is reflected in theinfrared spectrum of these complexes. Whereas free CO vibrates at 2143 cm−1, its complexes tend to absorb near 1950 cm−1.
The compoundscyclohexanehexone or triquinoyl (C6O6) andcyclopentanepentone or leuconic acid (C5O5), which so far have been obtained only in trace amounts, can be regarded as polymers of carbon monoxide. At pressures exceeding 5GPa, carbon monoxide converts topolycarbonyl, a solid polymer that is metastable at atmospheric pressure but is explosive.[61][62]
Thermalcombustion is the most common source for carbon monoxide. Carbon monoxide is produced from the partial oxidation ofcarbon-containing compounds; it forms when there is not enough oxygen to producecarbon dioxide (CO2), such as when operating astove or aninternal combustion engine in an enclosed space.
A large quantity of CO byproduct is formed during the oxidative processes for the production of chemicals. For this reason, the process off-gases have to be purified.
Many methods have been developed for carbon monoxide production.[64]
A major industrial source of CO isproducer gas, a mixture containing mostly carbon monoxide and nitrogen, formed by combustion of carbon in air at high temperature when there is an excess of carbon. In an oven, air is passed through a bed ofcoke. The initially produced CO2 equilibrates with the remaining hot carbon to give CO.[65] The reaction of CO2 with carbon to give CO is described as theBoudouard reaction.[66] Above 800 °C, CO is the predominant product:
CO2 (g) + C (s) → 2 CO (g) (ΔHr = 170 kJ/mol)
Another source is "water gas", a mixture ofhydrogen and carbon monoxide produced via the endothermic reaction ofsteam and carbon:
H2O (g) + C (s) → H2 (g) + CO (g) (ΔHr = 131 kJ/mol)
Carbon monoxide is also a byproduct of the reduction of metaloxideores with carbon, shown in a simplified form as follows:
MO + C → M + CO
Carbon monoxide is also produced by the direct oxidation of carbon in a limited supply of oxygen or air.
2 C + O2 → 2 CO
Since CO is a gas, the reduction process can be driven by heating, exploiting the positive (favorable)entropy of reaction. TheEllingham diagram shows that CO formation is favored over CO2 in high temperatures.
Phosgene, useful for preparing isocyanates, polycarbonates, and polyurethanes, is produced by passing purified carbon monoxide andchlorine gas through a bed of porousactivated carbon, which serves as acatalyst. World production of this compound was estimated to be 2.74 million tonnes in 1989.[71]
CO + Cl2 → COCl2
Methanol is produced by thehydrogenation of carbon monoxide. In a related reaction, the hydrogenation of carbon monoxide is coupled to C−C bond formation, as in theFischer–Tropsch process where carbon monoxide is hydrogenated to liquid hydrocarbon fuels. This technology allowscoal or biomass to be converted to diesel.
In theCativa process, carbon monoxide and methanol react in the presence of a homogeneousiridiumcatalyst andhydroiodic acid to giveacetic acid. This process is responsible for most of the industrial production of acetic acid.
Carbon monoxide is a strong reductive agent and has been used inpyrometallurgy to reducemetals fromores since ancient times. Carbon monoxide strips oxygen off metal oxides, reducing them to pure metal in high temperatures, formingcarbon dioxide in the process. Carbon monoxide is not usually supplied as is, in the gaseous phase, in the reactor, but rather it is formed in high temperature in presence of oxygen-carrying ore, or a carboniferous agent such as coke, and high temperature. Theblast furnace process is a typical example of a process of reduction of metal from ore with carbon monoxide.
Carbon monoxide has been proposed for use as a fuel on Mars by NASA researcherGeoffrey Landis.Carbon monoxide/oxygen engines have been suggested for early surface transportation use as both carbon monoxide and oxygen can be straightforwardly produced from the carbon dioxideatmosphere of Mars byzirconiaelectrolysis, without using anyMartian water resources to obtain hydrogen, which would be needed to make methane or any hydrogen-based fuel.[72]
Landis also proposed manufacturing the fuel from the similar carbon dioxide atmosphere of Venus for a sample return mission, in combination with solar-powered UAVs and rocket balloon ascent.[73]
Carbon monoxide is a bioactive molecule which acts as agaseous signaling molecule. It is naturally produced by many enzymatic and non-enzymatic pathways,[75] the best understood of which is the catabolic action ofheme oxygenase on theheme derived fromhemoproteins such ashemoglobin.[76] Following the first report that carbon monoxide is a normal neurotransmitter in 1993,[53] carbon monoxide has received significant clinical attention as a biological regulator.
Because of carbon monoxide's role in the body, abnormalities in its metabolism have been linked to a variety of diseases, including neurodegenerations, hypertension, heart failure, and pathological inflammation.[77] In many tissues, carbon monoxide acts asanti-inflammatory,vasodilatory, and encouragers ofneovascular growth.[78] In animal model studies, carbon monoxide reduced the severity of experimentally induced bacterialsepsis, pancreatitis, hepaticischemia/reperfusion injury, colitis, osteoarthritis, lung injury, lung transplantation rejection, and neuropathic pain while promoting skin wound healing. Therefore, there is significant interest in the therapeutic potential of carbon monoxide becoming pharmaceutical agent and clinical standard of care.[79]
Studies involving carbon monoxide have been conducted in many laboratories throughout the world for its anti-inflammatory and cytoprotective properties.[80] These properties have the potential to be used to prevent the development of a series of pathological conditions including ischemia reperfusion injury, transplant rejection, atherosclerosis, severe sepsis, severe malaria, or autoimmunity.[79] Many pharmaceutical drug delivery initiatives have developed methods to safely administer carbon monoxide, and subsequent controlled clinical trials have evaluated the therapeutic effect of carbon monoxide.[81]
Microbiota may also utilize carbon monoxide as agasotransmitter.[82] Carbon monoxide sensing is a signaling pathway facilitated by proteins such asCooA.[83][84][85] The scope of the biological roles for carbon monoxide sensing is still unknown.
The human microbiome produces, consumes, and responds to carbon monoxide.[75] For example, in certain bacteria, carbon monoxide is produced via thereduction of carbon dioxide by the enzymecarbon monoxide dehydrogenase with favorablebioenergetics to power downstream cellular operations.[86][75] In another example, carbon monoxide is a nutrient formethanogenic archaea which reduce it to methane using hydrogen.[87]
Carbon monoxide has certain antimicrobial properties which have been studied to treat against infectious diseases.[75]
Carbon monoxide is used inmodified atmosphere packaging systems in the US, mainly with fresh meat products such as beef, pork, and fish to keep them looking fresh. The benefit is two-fold: carbon monoxide protects against microbial spoilage and it enhances the meat color for consumer appeal.[88] The carbon monoxide combines withmyoglobin to form carboxymyoglobin, a bright-cherry-red pigment. Carboxymyoglobin is more stable than the oxygenated form of myoglobin, oxymyoglobin, which can become oxidized to the brown pigmentmetmyoglobin. This stable red color can persist much longer than in normally packaged meat. Typical levels of carbon monoxide used in the facilities that use this process are between 0.4% and 0.5%.[88]
The technology was first given "generally recognized as safe" (GRAS) status by theU.S. Food and Drug Administration (FDA) in 2002 for use as a secondary packaging system, and does not require labeling. In 2004, the FDA approved CO as primary packaging method, declaring that CO does not mask spoilage odor.[89] The process is currently unauthorized in many other countries, including Japan,Singapore, and theEuropean Union.[90][91][92]
Humans have maintained a complex relationship with carbon monoxide since first learning to control fire circa 800,000 BC. Early humans probably discovered the toxicity of carbon monoxide poisoning upon introducing fire into their dwellings. The early development ofmetallurgy andsmelting technologies emerging circa 6,000 BC through theBronze Age likewise plagued humankind from carbon monoxide exposure. Apart from the toxicity of carbon monoxide, indigenousNative Americans may have experienced the neuroactive properties of carbon monoxide throughshamanistic fireside rituals.[53]
Early civilizations developed mythological tales to explain the origin of fire, such asPrometheus fromGreek mythology who shared fire with humans.Aristotle (384–322 BC) first recorded that burning coals produced toxic fumes. Greek physicianGalen (129–199 AD) speculated that there was a change in the composition of the air that caused harm when inhaled, and many others of the era developed a basis of knowledge about carbon monoxide in the context ofcoal fume toxicity.Cleopatra may havedied fromcarbon monoxide poisoning.[53]
Georg Ernst Stahl mentionedcarbonarii halitus in 1697 in reference to toxic vapors thought to be carbon monoxide.Friedrich Hoffmann conducted the first modern scientific investigation into carbon monoxide poisoning from coal in 1716.Herman Boerhaave conducted the first scientific experiments on the effect of carbon monoxide (coal fumes) on animals in the 1730s.[53]
Joseph Priestley is considered to have first synthesized carbon monoxide in 1772.Carl Wilhelm Scheele similarly isolated carbon monoxide from charcoal in 1773 and thought it could be the carbonic entity making fumes toxic.Torbern Bergman isolated carbon monoxide fromoxalic acid in 1775. Later in 1776, the French chemistde Lassone [fr] produced CO by heatingzinc oxide withcoke, but mistakenly concluded that the gaseous product washydrogen, as it burned with a blue flame. In the presence of oxygen, including atmospheric concentrations, carbon monoxide burns with a blue flame, producing carbon dioxide.Antoine Lavoisier conducted similar inconclusive experiments to Lassone in 1777. The gas was identified as a compound containingcarbon andoxygen byWilliam Cruickshank in 1800.[53][94]
Thomas Beddoes andJames Watt recognized carbon monoxide (ashydrocarbonate) to brighten venous blood in 1793. Watt suggested coal fumes could act as an antidote to the oxygen in blood, and Beddoes and Watt likewise suggested hydrocarbonate has a greater affinity for animal fiber than oxygen in 1796. In 1854,Adrien Chenot similarly suggested carbon monoxide to remove the oxygen from blood and then be oxidized by the body to carbon dioxide.[53] The mechanism for carbon monoxide poisoning is widely credited toClaude Bernard whose memoirs beginning in 1846 and published in 1857 phrased, "prevents arterials blood from becoming venous".Felix Hoppe-Seyler independently published similar conclusions in the following year.[53]
Carbon monoxide gained recognition as an essential reagent in the 1900s.[5] Three industrial processes illustrate its evolution in industry. In theFischer–Tropsch process, coal and related carbon-rich feedstocks are converted into liquid fuels via the intermediacy of CO. Originally developed as part of the German war effort to compensate for their lack of domestic petroleum, this technology continues today. Also in Germany, a mixture of CO and hydrogen was found to combine witholefins to givealdehydes. This process, calledhydroformylation, is used to produce many large scale chemicals such assurfactants as well as specialty compounds that are popular fragrances and drugs. For example, CO is used in the production ofvitamin A.[95] In a third major process, attributed to researchers atMonsanto, CO combines with methanol to giveacetic acid. Most acetic acid is produced by theCativa process. Hydroformylation and the acetic acid syntheses are two of myriadcarbonylation processes.
^Holman, Jack P. (2002).Heat transfer (9th ed.). New York, NY: McGraw-Hill Companies, Inc. pp. 600–606.ISBN9780072406559.OCLC46959719.
^Incropera 1 Dewitt 2 Bergman 3 Lavigne 4, Frank P. 1 David P. 2 Theodore L. 3 Adrienne S. 4 (2007).Fundamentals of heat and mass transfer (6th ed.). Hoboken, NJ: John Wiley and Sons, Inc. pp. 941–950.ISBN9780471457282.OCLC62532755.{{cite book}}: CS1 maint: numeric names: authors list (link)
^Little, L. H.; Amberg, C. H. (1962). "Infrared Spectra of Carbon Monoxide and Carbon Dioxide Adsorbed on Chromia–Alumina and on Alumina".Canadian Journal of Chemistry.40 (10):1997–2006.Bibcode:1962CaJCh..40.1997L.doi:10.1139/v62-306.
^Scuseria, Gustavo E.; Miller, Michael D.; Jensen, Frank; Geertsen, Jan (1991). "The dipole moment of carbon monoxide".J. Chem. Phys.94 (10): 6660.Bibcode:1991JChPh..94.6660S.doi:10.1063/1.460293.
^Martinie, Ryan J.; Bultema, Jarred J.; Vander Wal, Mark N.; Burkhart, Brandon J.; Vander Griend, Douglas A.; DeKock, Roger L. (2011-08-01). "Bond Order and Chemical Properties of BF, CO, and N2".Journal of Chemical Education.88 (8):1094–1097.Bibcode:2011JChEd..88.1094M.doi:10.1021/ed100758t.ISSN0021-9584.S2CID11905354.
^Ulrich, Henri (2009).Cumulenes in click reactions. Wiley InterScience (Online service). Chichester, U.K.: Wiley. p. 45.ISBN9780470747957.OCLC476311784.
^Lupinetti, Anthony J.; Fau, Stefan; Frenking, Gernot; Strauss, Steven H. (1997). "Theoretical Analysis of the Bonding between CO and Positively Charged Atoms".J. Phys. Chem. A.101 (49):9551–9559.Bibcode:1997JPCA..101.9551L.doi:10.1021/jp972657l.
^Meerts, W; De Leeuw, F.H.; Dymanus, A. (1 June 1977). "Electric and magnetic properties of carbon monoxide by molecular-beam electric-resonance spectroscopy".Chemical Physics.22 (2):319–324.Bibcode:1977CP.....22..319M.doi:10.1016/0301-0104(77)87016-X.
^Stefan, Thorsten; Janoschek, Rudolf (2000). "How relevant are S=O and P=O Double Bonds for the Description of the Acid Molecules H2SO3, H2SO4, and H3PO3, respectively?".Journal of Molecular Modeling.6 (2):282–288.doi:10.1007/PL00010730.S2CID96291857.
^Source for figures: Carbon dioxide,NOAA Earth System Research Laboratory, (updated 2010.06). Methane,IPCCTAR table 6.1Archived 2007-06-15 at theWayback Machine, (updated to 1998). The NASA total was 17 ppmv over 100%, and CO2 was increased here by 15 ppmv. To normalize,N2 should be reduced by about 25 ppmv andO2 by about 7 ppmv.
^Committee on Medical and Biological Effects of Environmental Pollutants (1977).Carbon Monoxide. Washington, D.C.: National Academy of Sciences. p. 29.ISBN978-0-309-02631-4.
^Gosink T (January 28, 1983)."What Do Carbon Monoxide Levels Mean?".Alaska Science Forum. Geophysical Institute, University of Alaska Fairbanks. Archived fromthe original on December 25, 2008. RetrievedDecember 16, 2008.
^Seinfeld, John; Pandis, Spyros (2006).Atmospheric Chemistry and Physics: From Air Pollution to Climate Change. John Wiley & Sons.ISBN978-0-471-72018-8.
^abPenney, David; Benignus, Vernon; Kephalopoulos, Stylianos; Kotzias, Dimitrios; Kleinman, Michael; Verrier, Agnes (2010),"Carbon monoxide",WHO Guidelines for Indoor Air Quality: Selected Pollutants, World Health Organization,ISBN978-92-890-0213-4,OCLC696099951,archived from the original on March 8, 2021, retrievedMarch 18, 2024
^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
^Büchner, W.; Weiss, E. (1964). "Zur Kenntnis der sogenannten "Alkalicarbonyle" IV[1] Über die Reaktion von geschmolzenem Kalium mit Kohlenmonoxid".Helvetica Chimica Acta.47 (6):1415–1423.doi:10.1002/hlca.19640470604.
^Katz, Allen I.; Schiferl, David; Mills, Robert L. (1984). "New phases and chemical reactions in solid carbon monoxide under pressure".The Journal of Physical Chemistry.88 (15):3176–3179.doi:10.1021/j150659a007.
^Zheng, Yun; Wang, Jianchen; Yu, Bo; Zhang, Wenqiang; Chen, Jing; Qiao, Jinli; Zhang, Jiujun (2017). "A review of high temperature co-electrolysis of H O and CO to produce sustainable fuels using solid oxide electrolysis cells (SOECs): advanced materials and technology".Chem. Soc. Rev.46 (5):1427–1463.doi:10.1039/C6CS00403B.PMID28165079.
