Carbon monoxide

Athanor · official

CO · 28.01 g/mol

Also called carbonous oxide

Inorganic

Open in Athanor

Drawn from its SMILES with RDKit

DangerExtremely flammable gas · Toxic if inhaled

Names and identifiers

IUPAC name: carbon monoxide
Synonyms: carbonous oxide, carbon monooxide, Carbonic oxide
+ 35 more
Carbon oxide (CO), carbon(II) oxide, Exhaust gas, Flue gas, monoxide, Kohlenmonoxid, Koolmonoxyde, Kohlenoxyd, Wegla tlenek, Oxyde de carbone, Carbone (oxyde de), Carboneum oxygenisatum, Carbonio (ossido di), DTXSID5027273, 7U1EE4V452, CHEBI:17245, Monoxide, Carbon, RefChem:6405, DTXCID407273, carbon monooxide;carbon monoxide;carbon(II) oxide, 211-128-3, CARBON MONOXIDE (13C; 18O), Carbon monoxide [USAN], [CO], Carbon monoxide (USAN), Kohlenoxyd [German], Koolmonoxyde [Dutch], Kohlenmonoxid [German], Wegla tlenek [Polish], Oxyde de carbone [French], C#O, Carbone (oxyde de) [French], HSDB 903, Carbonio (ossido di) [Italian], EINECS 211-128-3
Molecular formula: CO
Empirical formula: CO
Molecular weight: 28.01 g/mol
Exact mass: 27.99491
CAS number: 630-08-0
PubChem CID: 281
Canonical SMILES: [C-]#[O+]
Isomeric SMILES: [C-]#[O+]
InChI: InChI=1S/CO/c1-2
InChIKey: UGFAIRIUMAVXCW-UHFFFAOYSA-N
Molfile

Names, InChI and the identifiers from PubChem, retrieved 2026-10-14.

Physical properties

TemperaturePressureDensity

Appearance: Colorless gas [Note: Shipped as a nonliquefied or liquefied compressed gas].[6]
7 values
From Hazardous Substances Data Bank (HSDB), the most authoritative source here.
Value As written Source
– Carbon monoxide is a colorless, odorless gas. Prolonged exposure to carbon monoxide rich atmospheres may be fatal. It is easily ignited. It is just lighter than air and a flame can flash back to the source of leak very easily. Under prolonged exposure to fire or intense heat the containers may violently rupture and rocket. [1] CAMEO Chemicals
– Carbon monoxide, refrigerated liquid (cryogenic liquid) appears as a colorless cryogenic liquid. Prolonged exposure to carbon monoxide rich atmospheres may be fatal. Contact with the liquid can cause severe frostbite. Less dense than air. Easily ignited and a flame can flash back to the source of a leak very easily. Burns with a violet flame. Under prolonged exposure to fire or intense heat the containers may rupture violently and rocket. It is used in organic synthesis, metallurgy, and a fuel. [1] CAMEO Chemicals
– CBI; Gas Vapor [2] EPA Chemical Data Reporting (CDR)
– ODOURLESS TASTELESS COLOURLESS COMPRESSED GAS. [3] ILO-WHO International Chemical Safety Cards (ICSCs)
– Colorless, odorless gas. [4] Occupational Safety and Health Administration (OSHA)
– Colorless, odorless gas. [Note: Shipped as a nonliquefied or liquefied compressed gas.] [5] The National Institute for Occupational Safety and Health (NIOSH)
–shown Colorless gas [Note: Shipped as a nonliquefied or liquefied compressed gas]. [6] Hazardous Substances Data Bank (HSDB)cites NIOSH. NIOSH Pocket Guide to Chemical Hazards & Other Databases CD-ROM. Department of Health & Human Services, Centers for Disease Prevention & Control. National Institute for Occupational Safety & Health. DHHS (NIOSH) Publication No. 2005-151 (2005)
Odor: Odorless[6]
Melting point: -205.02 °C[7]
6 values
5 of 5 sources agree on it (most common value).
Value As written Source
−199 °C -326 °F (USCG, 1999) [1] CAMEO Chemicalscites U.S. Coast Guard. 1999. Chemical Hazard Response Information System (CHRIS) - Hazardous Chemical Data. Commandant Instruction 16465.12C. Washington, D.C.: U.S. Government Printing Office.
−205 °C -337 °F (NIOSH, 2024) [1] CAMEO Chemicals
−205 °C -205 °C [3] ILO-WHO International Chemical Safety Cards (ICSCs)
−205 °C -337 °F [4] Occupational Safety and Health Administration (OSHA)
−205.0 °Cshown -205.02 °C [7] PAC Chemical Database, U.S. Department of Energy
−205 °C -337 °F [5] The National Institute for Occupational Safety and Health (NIOSH)
Boiling point: -191.5 °C @760 [mmHg][7]
6 values
5 of 5 sources agree on it (most common value).
Value As written Source
−191.5 °C -312.7 °F at 760 mmHg (USCG, 1999) [1] CAMEO Chemicalscites U.S. Coast Guard. 1999. Chemical Hazard Response Information System (CHRIS) - Hazardous Chemical Data. Commandant Instruction 16465.12C. Washington, D.C.: U.S. Government Printing Office.
−192 °C -313 °F at 760 mmHg (NIOSH, 2024) [1] CAMEO Chemicals
−191 °C -191 °C [3] ILO-WHO International Chemical Safety Cards (ICSCs)
−192 °C -313 °F [4] Occupational Safety and Health Administration (OSHA)
−191.5 °Cshown -191.5 °C @760 [mm Hg] [7] PAC Chemical Database, U.S. Department of Energy
−192 °C -313 °F [5] The National Institute for Occupational Safety and Health (NIOSH)
Density: 1.145 g/L[7]
4 values
Only one source reports it.
Value As written Source
– 0.791 at -312.7 °F (USCG, 1999) - Less dense than water [1] CAMEO Chemicalscites U.S. Coast Guard. 1999. Chemical Hazard Response Information System (CHRIS) - Hazardous Chemical Data. Commandant Instruction 16465.12C. Washington, D.C.: U.S. Government Printing Office.
– 0.791 at -312.7 °F [4] Occupational Safety and Health Administration (OSHA)
0.001145 g/mLshown 1.145 g/L [7] PAC Chemical Database, U.S. Department of Energy
– 0.97(relative gas density) [5] The National Institute for Occupational Safety and Health (NIOSH)
3 more values were reported but failed the checks (unreadable or out of range), so they are not shown.
Solubility in water: Solubility in water, ml/100ml at 20 °C: 2.3 (sparingly soluble)[3]
4 values
From ILO-WHO International Chemical Safety Cards (ICSCs), the most authoritative source here.
Value As written Source
– 2 % (NIOSH, 2024) [1] CAMEO Chemicals
– 2 % (NIOSH, 2024) [1] CAMEO Chemicals
–shown Solubility in water, ml/100ml at 20 °C: 2.3 (sparingly soluble) [3] ILO-WHO International Chemical Safety Cards (ICSCs)
– 2% [5] The National Institute for Occupational Safety and Health (NIOSH)
Vapor pressure: Reported, but no value passed the checks.
The 4 values and why
greater than 35 atm (NIOSH, 2024) (no temperature given; source [1])
greater than 35 atm (NIOSH, 2024) (no temperature given; source [1])
>35 atm (no temperature given; source [4])
>35 atm (no temperature given; source [5])
Autoignition temperature: 700 °C (1292 °F)[6]
3 values
Sources disagree; from Hazardous Substances Data Bank (HSDB), the most authoritative.
Value As written Source
609 °C 1128 °F (USCG, 1999) [1] CAMEO Chemicalscites U.S. Coast Guard. 1999. Chemical Hazard Response Information System (CHRIS) - Hazardous Chemical Data. Commandant Instruction 16465.12C. Washington, D.C.: U.S. Government Printing Office.
700 °Cshown 1292 °F (700 °C) [6] Hazardous Substances Data Bank (HSDB)cites Fire Protection Guide to Hazardous Materials. 13 ed. Quincy, MA: National Fire Protection Association, 2002., p. 49-39
605 °C 605 °C [3] ILO-WHO International Chemical Safety Cards (ICSCs)
Viscosity: Reported, but no value passed the checks.
The value and why
Viscosity gas at 273 K = 16.62 uN s/sq m (could not be read; source [6])
Refractive index: Reported, but no value passed the checks.
The value and why
Refractive index of gas = 1.0003364 at 273 K and 546.1 nm (could not be read; source [6])

Value	As written	Source
–	Carbon monoxide is a colorless, odorless gas. Prolonged exposure to carbon monoxide rich atmospheres may be fatal. It is easily ignited. It is just lighter than air and a flame can flash back to the source of leak very easily. Under prolonged exposure to fire or intense heat the containers may violently rupture and rocket.	[1] CAMEO Chemicals
–	Carbon monoxide, refrigerated liquid (cryogenic liquid) appears as a colorless cryogenic liquid. Prolonged exposure to carbon monoxide rich atmospheres may be fatal. Contact with the liquid can cause severe frostbite. Less dense than air. Easily ignited and a flame can flash back to the source of a leak very easily. Burns with a violet flame. Under prolonged exposure to fire or intense heat the containers may rupture violently and rocket. It is used in organic synthesis, metallurgy, and a fuel.	[1] CAMEO Chemicals
–	CBI; Gas Vapor	[2] EPA Chemical Data Reporting (CDR)
–	ODOURLESS TASTELESS COLOURLESS COMPRESSED GAS.	[3] ILO-WHO International Chemical Safety Cards (ICSCs)
–	Colorless, odorless gas.	[4] Occupational Safety and Health Administration (OSHA)
–	Colorless, odorless gas. [Note: Shipped as a nonliquefied or liquefied compressed gas.]	[5] The National Institute for Occupational Safety and Health (NIOSH)
–shown	Colorless gas [Note: Shipped as a nonliquefied or liquefied compressed gas].	[6] Hazardous Substances Data Bank (HSDB)cites NIOSH. NIOSH Pocket Guide to Chemical Hazards & Other Databases CD-ROM. Department of Health & Human Services, Centers for Disease Prevention & Control. National Institute for Occupational Safety & Health. DHHS (NIOSH) Publication No. 2005-151 (2005)

Value	As written	Source
−199 °C	-326 °F (USCG, 1999)	[1] CAMEO Chemicalscites U.S. Coast Guard. 1999. Chemical Hazard Response Information System (CHRIS) - Hazardous Chemical Data. Commandant Instruction 16465.12C. Washington, D.C.: U.S. Government Printing Office.
−205 °C	-337 °F (NIOSH, 2024)	[1] CAMEO Chemicals
−205 °C	-205 °C	[3] ILO-WHO International Chemical Safety Cards (ICSCs)
−205 °C	-337 °F	[4] Occupational Safety and Health Administration (OSHA)
−205.0 °Cshown	-205.02 °C	[7] PAC Chemical Database, U.S. Department of Energy
−205 °C	-337 °F	[5] The National Institute for Occupational Safety and Health (NIOSH)

Value	As written	Source
−191.5 °C	-312.7 °F at 760 mmHg (USCG, 1999)	[1] CAMEO Chemicalscites U.S. Coast Guard. 1999. Chemical Hazard Response Information System (CHRIS) - Hazardous Chemical Data. Commandant Instruction 16465.12C. Washington, D.C.: U.S. Government Printing Office.
−192 °C	-313 °F at 760 mmHg (NIOSH, 2024)	[1] CAMEO Chemicals
−191 °C	-191 °C	[3] ILO-WHO International Chemical Safety Cards (ICSCs)
−192 °C	-313 °F	[4] Occupational Safety and Health Administration (OSHA)
−191.5 °Cshown	-191.5 °C @760 [mm Hg]	[7] PAC Chemical Database, U.S. Department of Energy
−192 °C	-313 °F	[5] The National Institute for Occupational Safety and Health (NIOSH)

Value	As written	Source
–	0.791 at -312.7 °F (USCG, 1999) - Less dense than water	[1] CAMEO Chemicalscites U.S. Coast Guard. 1999. Chemical Hazard Response Information System (CHRIS) - Hazardous Chemical Data. Commandant Instruction 16465.12C. Washington, D.C.: U.S. Government Printing Office.
–	0.791 at -312.7 °F	[4] Occupational Safety and Health Administration (OSHA)
0.001145 g/mLshown	1.145 g/L	[7] PAC Chemical Database, U.S. Department of Energy
–	0.97(relative gas density)	[5] The National Institute for Occupational Safety and Health (NIOSH)

Value	As written	Source
–	2 % (NIOSH, 2024)	[1] CAMEO Chemicals
–	2 % (NIOSH, 2024)	[1] CAMEO Chemicals
–shown	Solubility in water, ml/100ml at 20 °C: 2.3 (sparingly soluble)	[3] ILO-WHO International Chemical Safety Cards (ICSCs)
–	2%	[5] The National Institute for Occupational Safety and Health (NIOSH)

Value	As written	Source
609 °C	1128 °F (USCG, 1999)	[1] CAMEO Chemicalscites U.S. Coast Guard. 1999. Chemical Hazard Response Information System (CHRIS) - Hazardous Chemical Data. Commandant Instruction 16465.12C. Washington, D.C.: U.S. Government Printing Office.
700 °Cshown	1292 °F (700 °C)	[6] Hazardous Substances Data Bank (HSDB)cites Fire Protection Guide to Hazardous Materials. 13 ed. Quincy, MA: National Fire Protection Association, 2002., p. 49-39
605 °C	605 °C	[3] ILO-WHO International Chemical Safety Cards (ICSCs)

Each value as its source reports it, with the source's number after it (listed under References). Where several sources report a property, the row shows the value most of them agree on, the rule the app uses; open the values to see every one.

Calculated

Heavy atoms: 2
Rings: 0
Aromatic rings: 0
Fraction sp³ carbons (Fsp3): 0
H-bond donors: 0
H-bond acceptors: 0 computed here · PubChem 1
Rotatable bonds: 0
TPSA (Å²): 19.9 computed here · PubChem 1
Formal charge: 0
XLogP3: 0.7 PubChem
Complexity: 10 PubChem
Stereocenters: None
Double-bond geometry: None specified
Point group: C∞v of one 3D conformer with its hydrogens, by Athanor’s engine (as in the app)

Elemental analysis

C42.88%
O57.12%

Isotope pattern

Each peak is a nominal mass with its abundance-weighted exact mass, as a percentage of the tallest, from IUPAC natural isotope abundances.

Computed from the structure with RDKit 2026.09 when this page was built, beside PubChem's own computed values from its record; where the two differ, both are shown.

Predicted

log P: -0.04 Crippen (Wildman and Crippen 1999)
log S (water solubility): 0.01 ESOL (Delaney 2004), log mol/L
Synthetic accessibility: 6.13 SA score, 1 easy to 10 hard (Ertl and Schuffenhauer 2009)

Drug-likeness: Lipinski’s rule of five

Molecular weight ≤ 500: 28.01
log P ≤ 5 (Crippen): -0.04
H-bond donors ≤ 5: 0
H-bond acceptors ≤ 10: 0

Passes all four rules.

¹³C NMR shifts, predicted

Predictions, not measurements; each names its method. A measured log P, where a source reports one, is under Physical properties.

Safety

Danger

Harmonized EU classification (CLP Annex VI). Source [8].

Flammable
Compressed gas
Acute toxicity
Health hazard

NFPA 704[6]

H220Extremely flammable gas
H331Toxic if inhaled

Precautionary statements: P203, P210, P222, P260, P261, P264, P270, P271, P280, P304+P340, P316, P318, P319, P321, P377, P381, P403, P403+P233, P405, P501

View all classifications (3)

[8] Regulation (EC) No 1272/2008 of the European Parliament and of the Council · DangerH220, H331
[9] European Chemicals Agency (ECHA) · 613 reports · DangerH220, H221, H280, H331, H360, H360D, H372
[9] European Chemicals Agency (ECHA) · 38 reports · DangerH220, H280, H331, H360, H372

Exposure limits

PEL-TWA (8-Hour Time Weighted Average): 50 ppm (55 mg/m³)[4]
PEL: TWA 50 ppm (55 mg/m3) See Appendix G[5]
REL-TWA (Time Weighted Average): 35 ppm (40 mg/m³)[4]
REL-C (Ceiling): 200 ppm (229 mg/m³)[4]
REL: TWA 35 ppm (40 mg/m3) C 200 ppm (229 mg/m3)[5]
TLV: 25 ppm as TWA; BEI issued.[3]

First aid

Excerpt from NIOSH Pocket Guide for Carbon monoxide: Eye: Frostbite - If eye tissue is frozen, seek medical attention immediately; if tissue is not frozen, immediately and thoroughly flush the eyes with large amounts of water for at least 15 minutes, occasionally lifting the lower and upper eyelids. If irritation, pain, swelling, lacrimation, or photophobia persist, get medical attention as soon as possible. Skin: Frostbite - If frostbite has occurred, seek medical attention immediately; do NOT rub the affected areas or flush them with water.[1]
Excerpt from NIOSH Pocket Guide for Carbon monoxide: Eye: Frostbite - If eye tissue is frozen, seek medical attention immediately; if tissue is not frozen, immediately and thoroughly flush the eyes with large amounts of water for at least 15 minutes, occasionally lifting the lower and upper eyelids. If irritation, pain, swelling, lacrimation, or photophobia persist, get medical attention as soon as possible. Skin: Frostbite - If frostbite has occurred, seek medical attention immediately; do NOT rub the affected areas or flush them with water.[1]
General First Aid: · Call 911 or emergency medical service. · Ensure that medical personnel are aware of the material(s) involved, take precautions to protect themselves and avoid contamination. · Move victim to fresh air if it can be done safely. · Administer oxygen if breathing is difficult. · If victim is not breathing: -- DO NOT perform mouth-to-mouth resuscitation; the victim may have ingested or inhaled the substance. -- If equipped and pulse detected, wash face and mouth, then give artificial respiration using a proper respiratory medical device (bag-valve mask, pocket mask equipped…[10]
General First Aid: · Call 911 or emergency medical service. · Ensure that medical personnel are aware of the material(s) involved, take precautions to protect themselves and avoid contamination. · Move victim to fresh air if it can be done safely. · Administer oxygen if breathing is difficult. · If victim is not breathing: -- DO NOT perform mouth-to-mouth resuscitation; the victim may have ingested or inhaled the substance. -- If equipped and pulse detected, wash face and mouth, then give artificial respiration using a proper respiratory medical device (bag-valve mask, pocket mask equipped…[10]

Storage

Fireproof. Cool. Keep in a well-ventilated room.[3]
Store in a cool, dry, well-ventilated location.[6]
Remove the sources of ignition. Electric installation should be explosion-proof construction. Protect container against sunlight, and store in well-ventilated, safe areas.[6]

Incompatibilities

May react vigorously with oxygen, acetylene, chlorine, fluorine, nitrous oxide.[6]
Strong oxidizers, bromine trifluoride, chlorine trifluoride, lithium.[6]
... Explosion (occurred) during reduction of iron oxide with carbon monoxide (due to) formation of pentacarbonyliron at temperatures between 0 and 150 °C.[6]
Carbon monoxide is exothermically oxidized over silver oxide, and the temperature may attain 300 °C.[6]

Safety data sheets on the supplier’s page: LGC Standards, CymitQuimica, Cooke Chemical Co., Ltd.

Always read the supplier’s safety data sheet before working with it.

Spectra

GC-MSSpectraBase
Vapor Phase IRSpectraBase

Experimental spectra held by these sources; each link opens the source's own record.

Literature

Reading PubChem, OpenAlex and GSRS…

Bioactivity

Reading ChEMBL…

References

[1]CAMEO Chemicals · Public domain (NOAA) · via PubChem · retrieved 2026-10-14
[2]EPA Chemical Data Reporting (CDR) · Public domain (US EPA) · via PubChem · retrieved 2026-10-14
[3]ILO-WHO International Chemical Safety Cards (ICSCs) · CC BY 4.0 · via PubChem · retrieved 2026-10-14
[4]Occupational Safety and Health Administration (OSHA) · Public domain (US DOL) · via PubChem · retrieved 2026-10-14
[5]The National Institute for Occupational Safety and Health (NIOSH) · Public domain (US CDC) · via PubChem · retrieved 2026-10-14
[6]Hazardous Substances Data Bank (HSDB) · Public domain (US NLM) · via PubChem · retrieved 2026-10-14
[7]PAC Chemical Database, U.S. Department of Energy · Public domain (US DOE) · via PubChem · retrieved 2026-10-14
[8]Regulation (EC) No 1272/2008 of the European Parliament and of the Council · EU reuse policy, CC BY 4.0 · via PubChem · retrieved 2026-10-14
[9]European Chemicals Agency (ECHA) · ECHA legal notice: reuse with acknowledgement · via PubChem · retrieved 2026-10-14
[10]Emergency Response Guidebook (ERG) · Public domain (US DOT) · via PubChem · retrieved 2026-10-14
[11]SpectraBase · Linked only · via PubChem · retrieved 2026-10-14
·Calculated values: computed by Athanor with RDKit 2026.09 from the structure.
·Literature on PubChem

Data last updated 2026-10-14.