Acetylene

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"HCCH" redirects here. For other uses, see HCCH (disambiguation).
Not to be confused with ethene.
Acetylene
Acetylene
Acetylene
Acetylene – space-filling model
space-filling model of solid acetylene
Names
IUPAC name
Ethyne
Systematic IUPAC name
Ethyne[1]
Identifiers
74-86-2 YesY
ChEBI CHEBI:27518 YesY
ChEMBL ChEMBL116336 YesY
ChemSpider 6086 YesY
Jmol 3D model Interactive image
KEGG C01548 YesY
UNII OC7TV75O83 YesY
UN number 1001 (dissolved)
3138 (in mixture with ethylene and propylene)
Properties
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
−84 °C; −119 °F; 189 K (1 atm)
slightly soluble
Vapor pressure 44.2 atm (20 °C)[2]
Acidity (pKa) 25[3]
Structure
Linear
Thermochemistry
201 J·mol−1·K−1
+226.88 kJ/mol
Hazards
NFPA 704
Flammability code 4: Will rapidly or completely vaporize at normal atmospheric pressure and temperature, or is readily dispersed in air and will burn readily. Flash point below 23 °C (73 °F). E.g., propane Health code 1: Exposure would cause irritation but only minor residual injury. E.g., turpentine Reactivity code 3: Capable of detonation or explosive decomposition but requires a strong initiating source, must be heated under confinement before initiation, reacts explosively with water, or will detonate if severely shocked. E.g., fluorine Special hazards (white): no codeNFPA 704 four-colored diamond
300 °C (572 °F; 573 K)
US health exposure limits (NIOSH):
PEL (Permissible)
none[2]
REL (Recommended)
C 2500 ppm (2662 mg/m3)[2]
IDLH (Immediate danger)
N.D.[2]
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
YesY verify (what is YesYN ?)
Infobox references

Acetylene (systematic name: ethyne) is the chemical compound with the formula C2H2. It is a hydrocarbon and the simplest alkyne.[4] 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.[5] Pure acetylene is odorless, but commercial grades usually have a marked odor due to impurities.[6]

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°.

Discovery[edit]

Acetylene was discovered in 1836 by Edmund Davy, who identified it as a "new carburet of hydrogen".[7][8] It was rediscovered in 1860 by French chemist Marcellin Berthelot, who coined the name "acétylène".[9] Berthelot's empirical formula for acetylene (C4H2), as well as the alternative name "quadricarbure d'hydrogène" (hydrogen quadricarbide) were incorrect because chemists at that time used the wrong atomic mass for carbon (6 instead of 12). Berthelot was able to prepare this gas by passing vapours of organic compounds (methanol, ethanol, etc.) through a red-hot tube and collecting the effluent. He also found acetylene was formed by sparking electricity through mixed cyanogen and hydrogen gases. Berthelot later obtained acetylene directly by passing hydrogen between the poles of a carbon arc.[10][11] Commercially available acetylene gas could smell foul due to the common impurities hydrogen sulphide and phosphine. However, as purity increases it will become odourless.

Preparation[edit]

Since the 1950s, acetylene has mainly been manufactured by the partial combustion of methane[5][12][13] or appears as a side product in the ethylene stream from cracking of hydrocarbons. Approximately 400,000 tonnes were produced by this method in 1983.[5] 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.[14]

Until the 1950s, when oil supplanted coal as the chief source of reduced carbon, acetylene (and the aromatic fraction from coal tar) was the main source of organic chemicals in the chemical industry. It was prepared by the hydrolysis of calcium carbide, a reaction discovered by Friedrich Wöhler in 1862[15] and still familiar to students:

CaC2 + 2H2O → Ca(OH)2 + C2H2

Calcium carbide production requires extremely 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.[16]

Bonding[edit]

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.[17]

Since acetylene is a linear symmetrical molecule, it possesses the D∞h point group.[18]

Physical properties[edit]

Changes of state[edit]

At atmospheric pressure, acetylene cannot exist as a liquid and does not have a melting point. The triple point on the phase diagram corresponds to the melting point (−80.8 °C) at the minimum pressure at which liquid acetylene can exist (1.27 atm). At temperatures below the triple point, solid acetylene can change directly to the vapour (gas) by sublimation. The sublimation point at atmospheric pressure is −84 °C.

Other[edit]

The adiabatic flame temperature in air at atmospheric pressure is 2534 °C.

Acetylene gas can be dissolved in acetone or dimethylformamide in room temperature and 1 atm.

Reactions[edit]

Metal acetylides[edit]

Since acetyene has a pKa of 25, acetylene can be deprotonated by a superbase to form an acetylide:[19]

HC≡CH + RM → RH + HC≡CM

Various organometallic[20] and inorganic[21] reagents are effective. The formation of the acetylide depends upon several factors such as the pKb of the base, the valency of the metal, and solvent characteristics.[19]

Copper(I) acetylide and silver acetylide can be formed in aqueous solutions with especial ease due to a poor solubility equilibrium.[19]

Reppe chemistry[edit]

Walter Reppe discovered that in the presence of metal catalysts, acetylene can react to give a wide range of industrially significant chemicals.[22][23]

Reppe-chemnistry-vinylization.png
Reppe-chemistry-endiol-V1.svg
1,4-Butynediol is produced industrially in this way from formaldehyde and acetylene.
Reppe-chemistry-carbonmonoxide-01.png
Reppe-chemistry-carbonmonoxide-02.png
Reppe-chemistry-benzene.png
Reppe-chemistry-cyclooctatetraene.png
at basic conditions(50-80 °C, 20-25 atm).

Applications[edit]

Welding[edit]

Approximately 20 percent of acetylene is supplied by the industrial gases industry for oxyacetylene gas welding and cutting due to the high temperature of the flame; combustion of acetylene with oxygen produces a flame of over 3,600 K (3,300 °C, 6,000 °F), releasing 11.8 kJ/g. Oxyacetylene is the hottest burning common fuel gas.[25] Acetylene is the third hottest natural chemical flame after dicyanoacetylene's 5260 K (4990 °C, 9010 °F) and cyanogen at 4798 K (4525 °C, 8180 °F). Oxy-acetylene welding was a very popular welding process in previous decades; however, the development and advantages of arc-based welding processes have made oxy-fuel welding nearly extinct for many applications. Acetylene usage for welding has dropped significantly. On the other hand, oxy-acetylene welding equipment is quite versatile – not only because the torch is preferred for some sorts of iron or steel welding (as in certain artistic applications), but also because it lends itself easily to brazing, braze-welding, metal heating (for annealing or tempering, bending or forming), the loosening of corroded nuts and bolts, and other applications. Bell Canada cable repair technicians still use portable acetylene fuelled torch kits as a soldering tool for sealing lead sleeve splices in manholes and in some aerial locations. Oxyacetylene welding may also be used in areas where electricity is not readily accessible. As well, oxy-fuel cutting is still very popular and oxy-acetylene cutting is utilized in nearly every metal fabrication shop. For use in welding and cutting, the working pressures must be controlled by a regulator, since above 15 psi,[26] if subjected to a shockwave (caused for example by a flashback),[27] acetylene will decompose explosively into hydrogen and carbon.

Acetylene fuel container/burner as used in the island of Bali

Portable lighting[edit]

Calcium carbide was used to generate acetylene used in the lamps for portable or remote applications. It was used for miners and cavers before the widespread use of incandescent lighting; or many years later low-power/high-lumen LED lighting; and is still used by mining industries in some nations without workplace safety laws. It was also used as an early light source for lighthouses.

Plastics and acrylic acid derivatives[edit]

Acetylene can be partially hydrogenated to ethylene, providing a feedstock for a variety of polyethylene plastics. Another major application of acetylene is its conversion to acrylic acid derivatives.[5] These derivatives form products such as acrylic fibers, glasses, paints, resins, and polymers.[24]

Niche applications[edit]

In 1881, the Russian chemist Mikhail Kucherov[28] 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.[29]

The polymerization of acetylene with Ziegler-Natta catalysts produces polyacetylene films. Polyacetylene, a chain of CH centres with alternating single and double bonds, was one of the first discovered organic semiconductors. Its reaction with iodine produces a highly electrically conducting material. Although such materials are not useful, these discoveries led to the developments of organic semiconductors, as recognized by the Nobel Prize in Chemistry in 2000 to Alan J. Heeger, Alan G MacDiarmid, and Hideki Shirakawa.[5]

In the early 20th century acetylene was widely used for illumination, including street lighting in some towns.[30] Most early automobiles used carbide lamps before the adoption of electric headlights.

Acetylene is sometimes used for carburization (that is, hardening) of steel when the object is too large to fit into a furnace.[31]

Acetylene is used to volatilize carbon in radiocarbon dating. The carbonaceous material in an archeological sample is treated with lithium metal in a small specialized research furnace to form lithium carbide (also known as lithium acetylide). The carbide can then be reacted with water, as usual, to form acetylene gas to be fed into mass spectrometer to measure the isotopic ratio of carbon-14 to carbon-12.[32]

Natural occurrence[edit]

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. A number of bacteria living on acetylene have been identified. The enzyme acetylene hydratase catalyzes the hydration of acetylene to give acetaldehyde.[33]

C2H2 + H2O → CH3CHO

Acetylene is a moderately common chemical in the universe, often associated with the atmospheres of gas giants.[34] 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 1,770 K 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.[35][36]

Safety and handling[edit]

Acetylene is not especially toxic but, when generated from calcium carbide, it can contain toxic impurities such as traces of phosphine and arsine, which give it a distinct garlic-like smell. It is also highly flammable, as most light hydrocarbons, hence its use in welding. Its most singular hazard is associated with its intrinsic instability, especially when it is pressurized: under certain conditions acetylene can react in an exothermic addition-type reaction to form a number of products, typically benzene and/or vinylacetylene, possibly in addition to carbon and hydrogen. Consequently, acetylene, if initiated by intense heat or a shockwave, can decompose explosively if the absolute pressure of the gas exceeds about 200 kPa (29 psi). Most regulators and pressure gauges on equipment report gauge pressure and the safe limit for acetylene therefore is 101 kPagage or 15 psig.[37] It is therefore supplied and stored dissolved in acetone or dimethylformamide (DMF),[38][39] contained in a gas cylinder with a porous filling (Agamassan), which renders it safe to transport and use, given proper handling. Information on safe storage of acetylene in upright cylinders is provided by the United States Mine Safety and Health Administration (MSHA).[40] Copper catalyses the decomposition of acetylene and as a result acetylene should not be transported in copper pipes. Brass pipe fittings should also be avoided.

References[edit]

  1. ^ Acyclic Hydrocarbons. Rule A-3. Unsaturated Compounds and Univalent Radicals, IUPAC Nomenclature of Organic Chemistry
  2. ^ a b c d "NIOSH Pocket Guide to Chemical Hazards #0008". National Institute for Occupational Safety and Health (NIOSH). 
  3. ^ [1], Gas Encyclopaedia, Air Liquide
  4. ^ R. H. Petrucci; W. S. Harwood; F. G. Herring (2002). General Chemistry (8th ed.). Prentice-Hall. p. 1072. 
  5. ^ a b c d e f g h Pässler, Peter; Hefner, Werner; Buckl, Klaus; Meinass, Helmut; Meiswinkel, Andreas; Wernicke, Hans-Jürgen; Ebersberg, Günter; Müller, Richard; Bässler, Jürgen; Behringer, Hartmut; Mayer, Dieter (2008). "Acetylene". Ullmann's Encyclopedia of Industrial Chemistry. doi:10.1002/14356007.a01_097.pub3. ISBN 3527306730. . Article Online Posting Date: 15 October 2008
  6. ^ Compressed Gas Association (1995) Material Safety and Data Sheet – Acetylene
  7. ^ Edmund Davy (August 1836) "Notice of a new gaseous bicarburet of hydrogen,", Report of the Sixth Meeting of the British Association for the Advancement of Science … , 5 : 62-63.
  8. ^ Miller, S.A. (1965). Acetylene: Its Properties, Manufacture and Uses 1. Academic Press Inc. 
  9. ^ Bertholet (1860) "Note sur une nouvelle série de composés organiques, le quadricarbure d'hydrogène et ses dérivés" (Note on a new series of organic compounds, tetra-carbon hydride and its derivatives), Comptes rendus, series 3, 50 : 805–808.
  10. ^ Berthelot (1862) "Synthèse de l'acétylène par la combinaison directe du carbone avec l'hydrogène" (Synthesis of acetylene by the direct combination of carbon with hydrogen), Comptes rendus, series 3, 54 : 640-644.
  11. ^ Acetylene
  12. ^ Habil, Phil; Sachsse, Hans (1954). "Herstellung von Acetylen durch unvollständige Verbrennung von Kohlenwasserstoffen mit Sauerstoff [Production of acetylene by incomplete combustion of hydrocarbons with oxygen]". Chemie Ingenieur Technik 26 (5): 245–253. doi:10.1002/cite.330260502. 
  13. ^ Habil, Phil; Bartholoméa, E. (1954). "Probleme großtechnischer Anlagen zur Erzeugung von Acetylen nach dem Sauerstoff-Verfahren [Problems of large-scale plants for the production of acetylene by the oxygen method]". Chemie Ingenieur Technik 26 (5): 253–258. doi:10.1002/cite.330260503. 
  14. ^ Acetylene: How Products are Made
  15. ^ Wohler (1862) "Bildung des Acetylens durch Kohlenstoffcalcium" (Formation of actylene by calcium carbide), Annalen der Chemie und Pharmacie, 124 : 220.
  16. ^ Freeman, Horace (1919). "Manufacture of Cyanamide". The Chemical News and the Journal of Physical Science 117: 232. Retrieved 23 December 2013. 
  17. ^ Organic Chemistry 7th ed. by J. McMurry, Thomson 2008
  18. ^ Housecroft, C. E.; Sharpe, A. G. (2008). Inorganic Chemistry (3rd ed.). Prentice Hall. pp. 94–95. ISBN 978-0131755536. 
  19. ^ a b c Viehe, Heinz Günter (1969). Chemistry of Acetylenes (1st ed.). New York: Marcel Dekker, inc. pp. 170–179 & 225–241. doi:10.1002/ange.19720840843. 
  20. ^ Midland, M. M.; McLoughlin, J. I.; Werley, Ralph T. (Jr.) (1990). "Preparation and Use of Lithium Acetylide: 1-Methyl-2-ethynyl-endo-3,3-dimethyl-2-norbornanol". Organic Syntheses 68: 14. doi:10.15227/orgsyn.068.0014. 
  21. ^ Coffman, Donald D. (1940). "Dimethylethhynylcarbinol". Organic Syntheses 40: 20. doi:10.15227/orgsyn.020.0040. 
  22. ^ Peter Pässler; Werner Hefner; Klaus Buckl; Helmut Meinass; Andreas Meiswinkel; Hans-Jürgen Wernicke; Günter Ebersberg; Richard Müller; Jürgen Bässler; Hartmut Behringer; Dieter Mayer (2007). "Acetylene". Ullmann's Encyclopedia of Industrial Chemistry: pg. 44. doi:10.1002/14356007.a01_097.pub2. Retrieved 26 December 2013. 
  23. ^ a b Reppe, Walter; Kutepow, N; Magin, A (1969). "Cyclization of Acetylenic Compounds". Angewandte Chemie International Edition in English 8 (10): 727–733. doi:10.1002/anie.196907271. Retrieved 26 December 2013. 
  24. ^ a b Takashi Ohara; Takahisa Sato; Noboru Shimizu; Günter Prescher; Helmut Schwind; Otto Weiberg; Klaus Marten; Helmut Greim (2003). "Acrylic Acid and Derivatives". Ullmann's Encyclopedia of Industrial Chemistry: pg. 7. doi:10.1002/14356007.a01_161.pub2. Retrieved 26 December 2013. 
  25. ^ "Acetylene". Products and Supply > Fuel Gases. Linde. Retrieved November 30, 2013. 
  26. ^ Acetylene - Properties, Purity and Packaging - Acetylene is simplest member of unsaturated hydrocarbons called alkynes or acetylenes. Most important of all starting materials ...
  27. ^ ESAB Oxy-acetylene welding handbook - Acetylene properties
  28. ^ Kutscheroff, M. (1881). "Ueber eine neue Methode direkter Addition von Wasser (Hydratation) an die Kohlenwasserstoffe der Acetylenreihe". Berichte der deutschen chemischen Gesellschaft 14: 1540–1542. doi:10.1002/cber.188101401320. 
  29. ^ Dmitry A. Ponomarev; Sergey M. Shevchenko (2007). "Hydration of Acetylene: A 125th Anniversary" (PDF). J. Chem. Ed. 84 (10): 1725. doi:10.1021/ed084p1725. 
  30. ^ The 100 most important chemical compounds: a reference guide
  31. ^ "Acetylene". Products and Services. BOC. Archived from the original on May 17, 2006. 
  32. ^ Geyh, Mebus (1990). "Radiocarbon dating problems using acetylene as counting gas". Radiocarbon 32 (3): 321–324. doi:10.2458/azu_js_rc.32.1278. Retrieved 26 December 2013. 
  33. ^ ten Brink, Felix (2014). "Chapter 2. Living on acetylene. A Primordial Energy Source". In Peter M.H. Kroneck and Martha E. Sosa Torres. The Metal-Driven Biogeochemistry of Gaseous Compounds in the Environment. Metal Ions in Life Sciences 14. Springer. pp. 15–35. doi:10.1007/978-94-017-9269-1_2. 
  34. ^ "Precursor to Proteins and DNA found in Stellar Disk" (Press release). W. M. Keck Observatory. 20 December 2005. 
  35. ^ Emily Lakdawalla (17 March 2006). "LPSC: Wednesday afternoon: Cassini at Enceladus". The Planetary Society. Archived from the original on 20 February 2012. 
  36. ^ John Spencer; David Grinspoon (25 January 2007). "Planetary science: Inside Enceladus". Nature 445 (7126): 376–377. doi:10.1038/445376b. PMID 17251967. 
  37. ^ "Acetylene Specification". CFC StarTec LLC. Retrieved 2012-05-02. 
  38. ^ Downie, N. A. (1997). Industrial Gases. London; New York: Blackie Academic & Professional. ISBN 978-0-7514-0352-7. 
  39. ^ Korzun, Mikołaj (1986). 1000 słów o materiałach wybuchowych i wybuchu. Warszawa: Wydawnictwo Ministerstwa Obrony Narodowej. ISBN 83-11-07044-X. OCLC 69535236. 
  40. ^ Special Hazards of Acetylene UNITED STATES DEPARTMENT OF LABOR Mine Safety and Health Administration - MSHA

External links[edit]