Ethyne
Athanor · official
C2H2 · 26.04 g/mol
IUPAC name: acetylene
Also called acetylene, welding gas
DangerExtremely flammable gasNames and identifiers
- IUPAC name
- acetylene
- Synonyms
- acetylene, welding gas, ACETYLENE
+ 37 more
Narcylen, Ethine, Acetylen, Vinylene, OC7TV75O83, DTXSID6026379, CHEBI:27518, acetylene;ethyne, RefChem:109145, DTXCID906379, 200-816-9, Azetylen, C2H2, Ethin, CH#CH, HC#CH, ACETYLENE (1,2-13C2), ACETYLENE (D1), [CH(CH)], Ethenylene, HSDB 166, EINECS 200-816-9, UN1001, UNII-OC7TV75O83, Dicarbon, Welding Gas, Acetylene, dissolved, Carbon (C2), Acetylene [WHO-DD], Des-Gln24-Tirzepatide, ACETYLENE [MI], ACETYLENE [HSDB], SCHEMBL428, EC 200-816-9, SCHEMBL3626, SCHEMBL65316, CHEMBL116336
- Molecular formula
- C2H2
- Empirical formula
- CH
- Molecular weight
- 26.04 g/mol
- Exact mass
- 26.01565
- CAS number
- 74-86-2
- PubChem CID
- 6326
- Canonical SMILES
- C#C
- Isomeric SMILES
- C#C
- InChI
- InChI=1S/C2H2/c1-2/h1-2H
- InChIKey
- HSFWRNGVRCDJHI-UHFFFAOYSA-N
- Molfile
Names, InChI and the identifiers from PubChem, retrieved 2026-10-14.
Physical properties
TemperaturePressureDensity
- Appearance
- Colorless gas ... [Note: Shipped under pressure dissolved in acetone][5]
5 values
From Hazardous Substances Data Bank (HSDB), the most authoritative source here.
Value As written Source – Acetylene appears as a colorless gas with a faint garlic-like odor. Easily ignited and burns with a sooty flame. Gas is lighter than air. Flame may flash back to the source of a leak very easily. Under prolonged exposure to fire or heat the containers may rupture violently and rocket. [1] CAMEO Chemicals – Liquid; Gas Vapor; CBI [2] EPA Chemical Data Reporting (CDR) – COLOURLESS GAS DISSOLVED IN ACETONE UNDER PRESSURE. [3] ILO-WHO International Chemical Safety Cards (ICSCs) – Colorless gas with a faint, ethereal odor. [Note: Commercial grade has a garlic-like odor. Shipped under pressure dissolved in acetone.] [4] The National Institute for Occupational Safety and Health (NIOSH) –shown Colorless gas ... [Note: Shipped under pressure dissolved in acetone] [5] Hazardous Substances Data Bank (HSDB)cites NIOSH. NIOSH Pocket Guide to Chemical Hazards. Department of Health & Human Services, Centers for Disease Control & Prevention. National Institute for Occupational Safety & Health. DHHS (NIOSH) Publication No. 2010-168 (2010). Available from: https://www.cdc.gov/niosh/npg - Odor
- Not unpleasant odor unless impure (due to phosphine)[5]
3 values
From Hazardous Substances Data Bank (HSDB), the most authoritative source here.
Value As written Source –shown Not unpleasant odor unless impure (due to phosphine) [5] Hazardous Substances Data Bank (HSDB)cites Armour, M.A. Hazardous Laboratory Chemicals Disposal Guide. Boca Raton, FL: CRC Press Inc., 1991., p. 11 – FAINT ODOR OF ETHER [5] Hazardous Substances Data Bank (HSDB)cites International Labour Office. Encyclopedia of Occupational Health and Safety. Vols. I&II. Geneva, Switzerland: International Labour Office, 1983., p. 40 – ... Faint, ethereal odor [Note: Commercial grade has a garlic-like odor ...] [5] Hazardous Substances Data Bank (HSDB)cites NIOSH. NIOSH Pocket Guide to Chemical Hazards. Department of Health & Human Services, Centers for Disease Control & Prevention. National Institute for Occupational Safety & Health. DHHS (NIOSH) Publication No. 2010-168 (2010). Available from: https://www.cdc.gov/niosh/npg - Melting point
- -84 °C (-119 °F) (Sublimes) (NIOSH, 2024)[1]
2 values
2 of 2 sources agree on it (most common value).
Value As written Source −84 °Cshown -119 °F (Sublimes) (NIOSH, 2024) [1] CAMEO Chemicals −84 °C -119 °F (Sublimes) [4] The National Institute for Occupational Safety and Health (NIOSH) 1 more value was reported but failed the checks (unreadable or out of range), so it is not shown.
- Boiling point
- Reported, but no value passed the checks.
The 3 values and why
- -119 °F at 760 mmHg (USCG, 1999) (boiling point at or below the melting point; source [1])
- BP: -84 °C sublimes (boiling point at or below the melting point; source [5])
- -84 °C @760 [mm Hg] (boiling point at or below the melting point; source [6])
- Density
- 0.909 @ 0°C[6]
3 values
2 of 3 sources agree on it (most common value).
Value As written Source – 0.613 at -112 °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. –shown 0.909 @ 0°C [6] PAC Chemical Database, U.S. Department of Energy – 0.91(relative gas density) [4] The National Institute for Occupational Safety and Health (NIOSH) - Solubility in water
- Solubility in water, g/100ml at 20 °C: 0.12[3]
6 values
From ILO-WHO International Chemical Safety Cards (ICSCs), the most authoritative source here.
Value As written Source – 2 % (NIOSH, 2024) [1] CAMEO Chemicals – In water, 1200 mg/L at 25 °C [5] Hazardous Substances Data Bank (HSDB)cites Yalkowsky, S.H., He, Yan, Jain, P. Handbook of Aqueous Solubility Data Second Edition. CRC Press, Boca Raton, FL 2010, p. 20 – Soluble in water and many organic materials [5] Hazardous Substances Data Bank (HSDB)cites International Labour Office. Encyclopedia of Occupational Health and Safety. Vols. I&II. Geneva, Switzerland: International Labour Office, 1983., p. 40 – Moderately soluble in ethanol and acetic acid; very soluble in Me2CO; almost miscible in ether [5] Hazardous Substances Data Bank (HSDB)cites Lewis, R.J. Sax's Dangerous Properties of Industrial Materials. 10th ed. Volumes 1-3 New York, NY: John Wiley & Sons Inc., 1999., p. V2: 43 –shown Solubility in water, g/100ml at 20 °C: 0.12 [3] ILO-WHO International Chemical Safety Cards (ICSCs) – 2% [4] The National Institute for Occupational Safety and Health (NIOSH) - log P
- 0.37[3]
2 values
2 of 2 sources agree on it (most common value).
Value As written Source – log Kow = 0.37 [5] Hazardous Substances Data Bank (HSDB)cites Hansch, C., Leo, A., D. Hoekman. Exploring QSAR - Hydrophobic, Electronic, and Steric Constants. Washington, DC: American Chemical Society., 1995., p. 4 –shown 0.37 [3] ILO-WHO International Chemical Safety Cards (ICSCs) - Vapor pressure
- 30780 [mmHg] @20 °C[6]
3 values
2 of 3 sources agree on it (most common value).
Value As written Source 30000 mmHg Vapor pressure = 40 atm at 16.8 °C [5] Hazardous Substances Data Bank (HSDB)cites Lewis, R.J. Sr. (ed) Sax's Dangerous Properties of Industrial Materials. 11th Edition. Wiley-Interscience, Wiley & Sons, Inc. Hoboken, NJ. 2004., p. 44 33000 mmHg Vapor pressure, kPa at 20 °C: 4460 [3] ILO-WHO International Chemical Safety Cards (ICSCs) 30780 mmHgshown 30780 [mm Hg] @20 °C [6] PAC Chemical Database, U.S. Department of Energy 2 more values were reported but failed the checks (unreadable or out of range), so they are not shown.
- Flash point
- Closed cup: -18.15 °C (-0.7 °F).[5]
- Autoignition temperature
- 305 °C[3]
3 values
3 of 3 sources agree on it (most common value).
Value As written Source 305 °C 581 °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. 305 °C 581 °F (305 °C) [5] Hazardous Substances Data Bank (HSDB)cites National Fire Protection Association; Fire Protection Guide to Hazardous Materials. 14TH Edition, Quincy, MA 2010, p. 325-10 305 °Cshown 305 °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
- Rotatable bonds
- 0
- TPSA (Ų)
- 0
- Formal charge
- 0
- XLogP3
- 0.4 PubChem
- Complexity
- 8 PubChem
- Stereocenters
- None
- Double-bond geometry
- None specified
- Point group
- D∞h of one 3D conformer with its hydrogens, by Athanor’s engine (as in the app)
Elemental analysis
- C92.26%
- H7.74%
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
- 0.25 Crippen (Wildman and Crippen 1999)
- log S (water solubility)
- -0.16 ESOL (Delaney 2004), log mol/L
- Synthetic accessibility
- 4.78 SA score, 1 easy to 10 hard (Ertl and Schuffenhauer 2009)
Drug-likeness: Lipinski’s rule of five
- Molecular weight ≤ 500: 26.04
- log P ≤ 5 (Crippen): 0.25
- 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 [7].
- Flammable
- Compressed gas
- H220Extremely flammable gas
Precautionary statements: P203, P210, P222, P280, P377, P381, P403
View all classifications (2)
- [7] Regulation (EC) No 1272/2008 of the European Parliament and of the Council · DangerH220
- [8] European Chemicals Agency (ECHA) · 455 reports · DangerH220, H280
First aid
- Excerpt from NIOSH Pocket Guide for Acetylene: 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…[9]
- (General first aid procedures) 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 - Compressed gases may create low temperatures when they expand rapidly. Leaks and uses that allow rapid expansion may cause a frostbite hazard.[4]
- Fresh air, rest. Artificial respiration may be needed. Refer for medical attention.[3]
Storage
- Fireproof. See Chemical Dangers. Cool.[3]
- Keep container in a cool, well-ventilated area. Keep container tightly closed and sealed until ready for use. Avoid all possible sources of ignition (spark or flame). Segregate from oxidizing materials. Cylinders should be stored upright, with valve protection cap in place, and firmly secured to prevent falling or being knocked over. Cylinder temperatures should not exceed 52 degC (125 degF).[5]
- Acetylene can be stored as a gas or in solution. Gaseous acetylene becomes highly explosive when compressed or heated and consequently it is stored under low pressure in large tanks or gasholders.[5]
- Outside or detached storage is preferred. Isolate from oxidizing gases, especially chlorine. Store in a cool , dry, well-ventilated location. Store cylinders upright. (acetylene, dissolved)[5]
Incompatibilities
- Mixture with air containing between 3-82% gas is explosive. Contact with /bleaching powder may lead to formation of explosive chloroacetylenes. Finely divided (cobalt) metal decomposes and polymerizes acetylene on contact, becoming incandescent. Copper metal forms explosive compounds with acetylene. If warmed in air or oxygen, or on impact, copper acetylides may explode in subsequent contact with acetylene. Interaction with (halogens) can be violent or explosive.[5]
- Contact of acetylene with the concn (nitric) acid in presence of mercury (II) salts forms trinitromethane, explosive above its mp, 15 °C. Subsequent addition of sulfuric acid produces tetranitromethane, a powerful oxidant of limited stability, in high yield.[5]
- Care is necessary with acetylene-fed atomic absorption spectroscopy (AAS) burners to prevent air being drawn up the liquid drainage line, when explosion is likely. While setting up an AAS instrument for use with nitrous oxide-acetylene, an explosion occurred shortly after switching from compressed air to the oxide, when the flame became unstable. This was attributed to the outdoor location of the nitrous oxide cylinder (at 5 °C) and the expansion cooling (4 °C) occurring in the reducing valve, combining to reduce the oxide flow to the point of flame instability and flashback.[5]
- A number of explosions have been experienced when using sample soln containing perchloric acid in atomic absorption spectrometers using acetylene-nitrous oxide flames ...[5]
Safety data sheets on the supplier’s page: AA BLOCKS, Cooke Chemical Co., Ltd, A2B Chem.
Always read the supplier’s safety data sheet before working with it.
Spectra
- 13C NMRSpectraBase
- GC-MSNIST Mass Spectrometry Data Center · NIST Mass Spectrometry Data Center · NIST Mass Spectrometry Data Center · SpectraBase
- Other MSHazardous Substances Data Bank (HSDB)
- IRHazardous Substances Data Bank (HSDB)
- Vapor Phase IRSpectraBase (DIGILAB FTS-14 · Vapor Phase)
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]The National Institute for Occupational Safety and Health (NIOSH) · Public domain (US CDC) · via PubChem · retrieved 2026-10-14
- [5]Hazardous Substances Data Bank (HSDB) · Public domain (US NLM) · via PubChem · retrieved 2026-10-14
- [6]PAC Chemical Database, U.S. Department of Energy · Public domain (US DOE) · via PubChem · retrieved 2026-10-14
- [7]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
- [8]European Chemicals Agency (ECHA) · ECHA legal notice: reuse with acknowledgement · via PubChem · retrieved 2026-10-14
- [9]Emergency Response Guidebook (ERG) · Public domain (US DOT) · via PubChem · retrieved 2026-10-14
- [10]SpectraBase · Linked only · via PubChem · retrieved 2026-10-14
- [11]NIST Mass Spectrometry Data Center · 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.