Acetylene
Names | |
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Preferred IUPAC name
Acetylene[1] | |
Systematic IUPAC name
Ethyne[2] | |
Identifiers | |
3D model (
JSmol ) |
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906677 | |
ChEBI | |
ChEMBL | |
ChemSpider | |
ECHA InfoCard
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100.000.743 |
EC Number |
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210 | |
KEGG | |
PubChem CID
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RTECS number
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UNII | |
UN number | ) |
CompTox Dashboard (EPA)
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Properties | |
C2H2 | |
Molar mass | 26.038 g·mol−1 |
Appearance | Colorless gas |
Odor | Odorless |
Density | 1.1772 g/L = 1.1772 kg/m3 (0 °C, 101.3 kPa)[3] |
Melting point | −80.8 °C (−113.4 °F; 192.3 K) Triple point at 1.27 atm |
−84 °C; −119 °F; 189 K (1 atm) | |
slightly soluble | |
Solubility | slightly soluble in alcohol soluble in acetone, benzene |
Vapor pressure | 44.2 atm (20 °C)[4] |
Acidity (pKa) | 25[5] |
Conjugate acid
|
Ethynium |
−20.8×10−6 cm3/mol [6] | |
Thermal conductivity
|
21.4 mW·m−1·K−1 (300 K) [6] |
Structure | |
Linear
| |
Thermochemistry[6] | |
Heat capacity (C)
|
44.036 J·mol−1·K−1 |
Std molar
entropy (S⦵298) |
200.927 J·mol−1·K−1 |
Std enthalpy of (ΔfH⦵298)formation |
227.400 kJ·mol−1 |
Gibbs free energy (ΔfG⦵)
|
209.879 kJ·mol−1 |
Std enthalpy of (ΔcH⦵298)combustion |
1300 kJ·mol−1 |
Hazards | |
GHS labelling: | |
Danger | |
H220, H336 | |
P202, P210, P233, P261, P271, P304, P312, P340, P377, P381, P403, P405, P501 | |
NFPA 704 (fire diamond) | |
300 °C (572 °F; 573 K) | |
Explosive limits
|
2.5–100% |
NIOSH (US health exposure limits): | |
PEL (Permissible)
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none[4] |
REL (Recommended)
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C 2500 ppm (2662 mg/m3)[4] |
IDLH (Immediate danger) |
N.D.[4] |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Acetylene (systematic name: ethyne) is the chemical compound with the formula C2H2 and structure H−C≡C−H. It is a hydrocarbon and the simplest alkyne.[7] This colorless gas is widely used as a fuel and a chemical building block. It is unstable in its pure form and thus is usually handled as a solution.[8] Pure acetylene is odorless, but commercial grades usually have a marked odor due to impurities such as divinyl sulfide and phosphine.[8][9]
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°.[10]
Discovery
Acetylene was discovered in 1836 by
Preparation
Except in China acetylene production is dominated by partial combustion of natural gas.[17]
Partial combustion of hydrocarbons
Since the 1950s, acetylene has mainly been manufactured by the partial combustion of methane.[18][19][20] It is a recovered side product in production of ethylene by cracking of hydrocarbons. Approximately 400,000 tonnes were produced by this method in 1983.[18] Its presence in ethylene is usually undesirable because of its explosive character and its ability to poison Ziegler–Natta catalysts. It is selectively hydrogenated into ethylene, usually using Pd–Ag catalysts.[21]
3 CH4 + 3 O2 → C2H2 + CO + 5 H2O.
Partial combustion of methane also produces acetylene:
Dehydrogenation of alkanes
The heaviest alkanes in petroleum and natural gas are cracked into lighter molecules which are dehydrogenated at high temperature:
- C2H6 → C2H2 + 2 H2
- 2 CH4→ C2H2+ 3 H2
This last reaction is implemented in the process of anaerobic decomposition of methane by microwave plasma. The advantage of this technology is the absence of CO2 emissions and the joint production of hydrogen as a secondary product.[22] It makes it a low-carbon technology production and also an electrified process. For 32 t of methane transformed, production of 26 t of acetylene and 6 t of hydrogen (according to stoichiometry).
Carbochemical method
Acetylene is traditionally produced by hydrolysis (reaction with water) of calcium carbide:
- CaC2 + 2 H2O → Ca(OH)2 + C2H2
1 kg of calcium carbide combines with 562.5 g of water to release 350 liters of acetylene. This reaction was discovered by Friedrich Wöhler in 1862.[23]
The use of this technology has declined worldwide with the notable exception of China, with its emphasis on coal-based chemical industry. Otherwise oil has increasingly supplanted coal as the chief source of reduced carbon.[24]
Calcium carbide production requires high temperatures, ~2000 °C, necessitating the use of an electric arc furnace. In the US, this process was an important part of the late-19th century revolution in chemistry enabled by the massive hydroelectric power project at Niagara Falls.[25]
Bonding
In terms of valence bond theory, in each carbon atom the 2s orbital hybridizes with one 2p orbital thus forming an sp hybrid. The other two 2p orbitals remain unhybridized. The two ends of the two sp hybrid orbital overlap to form a strong σ valence bond between the carbons, while on each of the other two ends hydrogen atoms attach also by σ bonds. The two unchanged 2p orbitals form a pair of weaker π bonds.[26]
Since acetylene is a linear symmetrical molecule, it possesses the D∞h point group.[27]
Physical properties
Changes of state
At atmospheric pressure, acetylene cannot exist as a liquid and does not have a melting point. The
Other
At room temperature, the solubility of acetylene in acetone is 27.9 g per kg. For the same amount of dimethylformamide (DMF), the solubility is 51 g. At 20.26 bar, the solubility increases to 689.0 and 628.0 g for acetone and DMF, respectively. These solvents are used in pressurized gas cylinders.[29]
Applications
Welding
Approximately 20% of acetylene is supplied by the
Chemicals
Acetylene, despite its simplicity, is not used for many industrial processes.
One of the major chemical applications is ethynylation of formaldehyde.[8] Acetylene adds to aldehydes and ketones to form α-ethynyl alcohols:
The reaction gives butynediol, with propargyl alcohol as the by-product. Copper acetylide is used as the catalyst.[32][33]
In addition to ethynylation, acetylene reacts with
Historical uses
Prior to the widespread use of petrochemicals, coal-derived acetylene was a building block for several industrial chemicals. Thus acetylene can be hydrated to give acetaldehyde, which in turn can be oxidized to acetic acid. Processes leading to acrylates were also commercialized. Almost all of these processes became obsolete with the availability of petroleum-derived ethylene and propylene.[35]
Niche applications
In 1881, the Russian chemist Mikhail Kucherov[36] described the hydration of acetylene to acetaldehyde using catalysts such as mercury(II) bromide. Before the advent of the Wacker process, this reaction was conducted on an industrial scale.[37]
The
In the 1920s, pure acetylene was experimentally used as an
Acetylene is sometimes used for
Acetylene is used to volatilize carbon in
Acetylene combustion produces a strong, bright light and the ubiquity of
Natural occurrence
The energy richness of the C≡C triple bond and the rather high solubility of acetylene in water make it a suitable substrate for bacteria, provided an adequate source is available.[45] A number of bacteria living on acetylene have been identified. The enzyme acetylene hydratase catalyzes the hydration of acetylene to give acetaldehyde:[46]
- C2H2 + H2O → CH3CHO
Acetylene is a moderately common chemical in the universe, often associated with the atmospheres of gas giants.[47] One curious discovery of acetylene is on Enceladus, a moon of Saturn. Natural acetylene is believed to form from catalytic decomposition of long-chain hydrocarbons at temperatures of 1,700 K (1,430 °C; 2,600 °F) and above. Since such temperatures are highly unlikely on such a small distant body, this discovery is potentially suggestive of catalytic reactions within that moon, making it a promising site to search for prebiotic chemistry.[48][49]
Reactions
Vinylation reactions
In
The hydration of acetylene is a vinylation reaction, but the resulting vinyl alcohol isomerizes to
Organometallic chemistry
Acetylene and its derivatives (2-butyne, diphenylacetylene, etc.) form complexes with transition metals. Its bonding to the metal is somewhat similar to that of ethylene complexes. These complexes are intermediates in many catalytic reactions such as alkyne trimerisation to benzene, tetramerization to cyclooctatetraene,[8] and carbonylation to hydroquinone:[51]
Metal
Acid-base reactions
Acetylene has a pKa of 25, acetylene can be deprotonated by a superbase to form an acetylide:[52]
Various
reagents are effective.Hydrogenation
Acetylene can be
Safety and handling
Acetylene is not especially toxic, but when generated from
Information on safe storage of acetylene in upright cylinders is provided by the OSHA,[60][61] Compressed Gas Association,[56] United States Mine Safety and Health Administration (MSHA),[62] EIGA,[59] and other agencies.
Copper catalyses the decomposition of acetylene, and as a result acetylene should not be transported in copper pipes.[63]
Cylinders should be stored in an area segregated from oxidizers to avoid exacerbated reaction in case of fire/leakage.[56][61] Acetylene cylinders should not be stored in confined spaces, enclosed vehicles, garages, and buildings, to avoid unintended leakage leading to explosive atmosphere.[56][61] In the US, National Electric Code (NEC) requires consideration for hazardous areas including those where acetylene may be released during accidents or leaks.[64] Consideration may include electrical classification and use of listed Group A electrical components in US.[64] Further information on determining the areas requiring special consideration is in NFPA 497.[65] In Europe, ATEX also requires consideration for hazardous areas where flammable gases may be released during accidents or leaks.[59]
References
- ISBN 978-0-85404-182-4.
The name acetylene is retained for the compound HC≡CH. It is the preferred IUPAC name, but substitution of any kind is not allowed; however, in general nomenclature, substitution is allowed, for example fluoroacetylene [fluoroethyne (PIN)], but not by alkyl groups or any other group that extends the carbon chain, nor by characteristic groups expressed by suffixes.
- ^ Acyclic Hydrocarbons. Rule A-3. Unsaturated Compounds and Univalent Radicals Archived 10 October 2000 at the Wayback Machine, IUPAC Nomenclature of Organic Chemistry
- ^ Record of Acetylene in the GESTIS Substance Database of the Institute for Occupational Safety and Health
- ^ a b c d NIOSH Pocket Guide to Chemical Hazards. "#0008". National Institute for Occupational Safety and Health (NIOSH).
- ^ "Acetylene – Gas Encyclopedia Air Liquide". Air Liquide. Archived from the original on 4 May 2022. Retrieved 27 September 2018.
- ^ )
- ^ R. H. Petrucci; W. S. Harwood; F. G. Herring (2002). General Chemistry (8th ed.). Prentice-Hall. p. 1072.
- ^ ISBN 978-3527306732.
- ^ Compressed Gas Association (1995) Material Safety and Data Sheet – Acetylene Archived 11 July 2012 at the Wayback Machine
- ISBN 0-03-072373-6.
- ^ Edmund Davy (August 1836) "Notice of a new gaseous bicarburet of hydrogen" Archived 6 May 2016 at the Wayback Machine, Report of the Sixth Meeting of the British Association for the Advancement of Science …, 5: 62–63.
- ^ Miller, S. A. (1965). Acetylene: Its Properties, Manufacture and Uses. Vol. 1. Academic Press Inc. Archived from the original on 15 April 2021. Retrieved 16 July 2021.
- ^ Bertholet (1860) "Note sur une nouvelle série de composés organiques, le quadricarbure d'hydrogène et ses dérivés" Archived 13 July 2015 at the Wayback Machine (Note on a new series of organic compounds, tetra-carbon hydride and its derivatives), Comptes rendus, series 3, 50: 805–808.
- doi:10.1021/ed038p83. Archivedfrom the original on 30 December 2021. Retrieved 29 December 2021.
Atomic weights of 6 and 12 were both in use for carbon.
- ^ Berthelot (1862) "Synthèse de l'acétylène par la combinaison directe du carbone avec l'hydrogène" Archived 14 August 2020 at the Wayback Machine (Synthesis of acetylene by the direct combination of carbon with hydrogen), Comptes rendus, series 3, 54: 640–644.
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- ^ "How it Works". Transform Materials. Retrieved 21 July 2023.
- ^ Wohler (1862) "Bildung des Acetylens durch Kohlenstoffcalcium" Archived 12 May 2016 at the Wayback Machine (Formation of actylene by calcium carbide), Annalen der Chemie und Pharmacie, 124: 220.
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- ^ Freeman, Horace (1919). "Manufacture of Cyanamide". The Chemical News and the Journal of Physical Science. 117: 232. Archived from the original on 15 April 2021. Retrieved 23 December 2013.
- ^ Organic Chemistry 7th ed. by J. McMurry, Thomson 2008
- ISBN 978-0-13-175553-6.
- ^ Handbook of Chemistry and Physics (60th ed., CRC Press 1979–80), p. C-303 in Table Physical Constants of Organic Compounds (listed as ethyne).
- ^ ISBN 978-3527306732.)
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: CS1 maint: numeric names: authors list (link - ^ "Acetylene". Products and Supply > Fuel Gases. Linde. Archived from the original on 12 January 2018. Retrieved 30 November 2013.
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- ^ "Lighthouse Lamps Through Time by Thomas Tag | US Lighthouse Society". uslhs.org. Archived from the original on 25 February 2017. Retrieved 24 February 2017.
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External links
- Acetylene Production Plant and Detailed Process Archived 11 April 2015 at the Wayback Machine
- Acetylene at Chemistry Comes Alive!
- Acetylene, the Principles of Its Generation and Use at Project Gutenberg
- Movie explaining acetylene formation from calcium carbide and the explosive limits forming fire hazards
- Calcium Carbide & Acetylene at The Periodic Table of Videos(University of Nottingham)
- CDC – NIOSH Pocket Guide to Chemical Hazards – Acetylene