Title: Acetylene
CAS Registry Number: 74-86-2
CAS Name: Ethyne
Additional Names: ethine
Molecular Formula: C2H2
Molecular Weight: 26.04
Percent Composition: C 92.25%, H 7.74%
Line Formula: HCºCH
Literature References: Manuf from calcium carbide and water: Eastman, US 3017259 (1962 to Texaco); from methane: Anderson, US 3051639 (1962 to Union Carbide). Toxicity data: Riggs, Proc. Soc. Exp. Biol. Med. 22, 269 (1925). Review of manuf processes: Faith, Keyes & Clark's Industrial Chemicals, F. A. Lowenheim, M. K. Moran, Eds. (Wiley-Interscience, New York, 4th ed., 1975) pp 26-35. Review: Nieuwland, Vogt, The Chemistry of Acetylene (Reinhold, New York, 1945) pp 1-219. Comprehensive monograph in 2 vols: S. A. Miller, Acetylene (Academic Press, New York, 1965); several authors in Kirk-Othmer Encyclopedia of Chemical Technology vol. 1 (Wiley-Interscience, New York, 3rd ed., 1978) pp 192-243.
Properties: Gas; odor not unpleasant when pure, but disagreeable when impure (due to phosphine). mp -81° (subl). At 0° liquifies at 21.5 atm; below 37° (crit temp) liquifies at 68 atm. One liter at 0° and 760 mm weighs 1.165 g; d gas (air = 1) 0.90. Burns brilliantly in air with very sooty flame. Heat of combustion 313 cal. Not explosive at ordinary atmospheric pressure, but at 2 atms or more it is explosive by spark or decomposition. Mixture with air containing more than 3% or less than 65% gas is explosive, max being 1 vol gas and 12.5 vol air. Forms insoluble explosive compounds with copper and silver; hence copper or brass containers must be avoided. One vol dissolves in 1 vol water, in 6 vols glacial acetic acid or alcohol; soluble in ether, benzene. Acetone dissolves 25 vols acetylene at 15° and 760 mm; but 300 vols at 12 atm. LC in rats: 900000 ppm (Riggs).
Density: d gas (air = 1) 0.90
Toxicity data: LC in rats: 900000 ppm (Riggs)
CAUTION: Potential symptoms of overexposure are headache, dizziness; asphyxia; direct contact with liquid may cause frostbite. See NIOSH Pocket Guide to Chemical Hazards (DHHS/NIOSH 97-140, 1997) p 4.
Use: Illuminant, oxyacetylene welding, cutting, and soldering metals, signalling; pptg metals, particularly Cu; manuf acetaldehyde, acetic acid; fuel for motor boats.
Acetylene Dibromide Acetylene Dichloride Acetyleneurea Acetylleucine Monoethanolamine Acetylpheneturide

Acetylene – space-filling model
space-filling model of solid acetylene
CAS number 74-86-2 YesY
ChemSpider 6086 YesY
UN number 1001 (dissolved)
3138 (in mixture with ethylene and propylene)
KEGG C01548 YesY
ChEBI CHEBI:27518 YesY
Jmol-3D images Image 1
Molecular formula C2H2
Molar mass 26.04 g mol−1
Density 1.097 g/L = 1.097 kg/m3
Melting point −80.8 °C; −113.4 °F; 192.3 K (Triple point at 1.27 atm)
Boiling point −84 °C; −119 °F; 189 K (Sublimation point at 1 atm)
Solubility in water slightly soluble
Acidity (pKa) 25[2]
Molecular shape Linear
Std molar
entropy So298
201 J·mol−1·K−1
Std enthalpy of
formation ΔfHo298
+226.88 kJ/mol
NFPA 704
NFPA 704.svg
Autoignition temperature 300 °C; 572 °F; 573 K
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Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
Infobox references

Acetylene (systematic name: ethyne) is the chemical compound with the formula C2H2. It is a hydrocarbon and the simplest alkyne.[3] This colorless gas is widely used as a fuel and a chemical building block. It is unstable in pure form and thus is usually handled as a solution.[4] Pure acetylene is odorless, but commercial grades usually have a marked odor due to impurities.[5]

As an alkyne, acetylene is unsaturated because its two carbon atoms are bonded together in a triple bond. The carbon–carbon triple bond places all four atoms in the same straight line, with CCH bond angles of 180°. Since acetylene is a linear symmetrical molecule, it possesses the D∞h point group.[6]