Acetylene 1

Acetylene

Acetylene

Identifiers

CAS number 74-86-2 [1]

ChemSpider 6086 [2]

UNII OC7TV75O83 [3]

UN number 1001 (dissolved)3138 (in mixture with ethylene and propylene)

KEGG C01548 [4]

ChEBI CHEBI:27518 [5]

ChEMBL CHEMBL116336 [6]

Jmol-3D images Image 1 [7]

Properties

Molecular formula C2H2Molar mass 26.04 g mol1

Density 1.097 g/L = 1.097 kg/m3

Melting point 80.8C; 113.4F; 192.3K (Triple point at 1.27 atm)

Boiling point 84C; 119F; 189K (Sublimation point at 1 atm)

Acetylene 2

Solubility in water slightly soluble

Acidity (pKa) 25[8]

Structure

Molecular shape Linear

Thermochemistry

Std molarentropy So298

201Jmol1K1

Std enthalpy offormation fH

o298

+226.88 kJ/mol

Hazards

NFPA 704

Autoignition temperature 300C; 572F; 573K

(verify) [9](what is: / ?)Except where noted otherwise, data are given for materials in their standard state (at 25C (77F), 100kPa)

Infobox references

Acetylene (systematic name: ethyne) is the chemical compound with the formula C2H2. It is a hydrocarbon and thesimplest alkyne.[10] This colorless gas is widely used as a fuel and a chemical building block. It is unstable in pureform and thus is usually handled as a solution. Pure acetylene is odorless, but commercial grades usually have amarked odor due to impurities.[11]

As an alkyne, acetylene is unsaturated because its two carbon atoms are bonded together in a triple bond. Thecarboncarbon triple bond places all four atoms in the same straight line, with CCH bond angles of 180. Sinceacetylene is a linear symmetrical molecule, it possesses the Dh point group.

DiscoveryAcetylene was discovered in 1836 by Edmund Davy, who identified it as a "new carburet of hydrogen". It wasrediscovered in 1860 by French chemist Marcellin Berthelot, who coined the name "acetylene". Berthelot was able toprepare this gas by passing vapours of organic compounds (methanol, ethanol, etc.) through a red-hot tube andcollecting the effluent. He also found acetylene was formed by sparking electricity through mixed cyanogen andhydrogen gases. Berthelot later obtained acetylene directly by passing hydrogen between the poles of a carbonarc.[12] Commercially available acetylene gas could smell foul due to the common impurities hydrogen sulphide andphosphine. However, acetylene gas with high purity would generate a light and sweet smell.

Acetylene 3

PreparationToday acetylene is mainly manufactured by the partial combustion of methane or appears as a side product in theethylene stream from cracking of hydrocarbons. Approximately 400,000 tonnes are produced by this methodannually.[] Its presence in ethylene is usually undesirable because of its explosive character and its ability to poisonZiegler-Natta catalysts. It is selectively hydrogenated into ethylene, usually using PdAg catalysts.[13]

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

CaC2 + 2H2O Ca(OH)2 + C2H2Calcium carbide production requires extremely high temperatures, ~2000C, necessitating the use of an electric arcfurnace. In the US, this process was an important part of the late-19th century revolution in chemistry enabled by themassive hydroelectric power project at Niagara Falls.

BondingIn terms of valence bond theory, in each carbon atom the 2s orbital hybridizes with one 2p orbital thus forming an sphybrid. The other two 2p orbitals remain unhybridized. The two ends of the two sp hybrid orbital overlap to form astrong valence bond between the carbons, while on each of the other two ends hydrogen atoms attach also by bonds. The two unchanged 2p orbitals form a pair of weaker valence bonds.[14]

Physical properties

Changes of stateAt atmospheric pressure, acetylene cannot exist as a liquid and does not have a melting point. The triple point on thephase diagram corresponds to the melting point (80.8C) at the minimum pressure at which liquid acetylene canexist (1.27 atm). At temperatures below the triple point, solid acetylene can change directly to the vapor (gas) bysublimation. The sublimation point at atmospheric pressure is 84C.

OtherThe adiabatic flame temperature in air at atmospheric pressure is 2534C.Acetylene gas can be dissolved in acetone or dimethylformamide in room temperature and 1 atm.

ReactionsOne new application is the conversion of acetylene to ethylene for use in making a variety of polyethylene plastics.An important reaction of acetylene is its combustion, the basis of the acetylene welding technologies. Otherwise, itsmajor applications involve its conversion to acrylic acid derivatives.Compared to most hydrocarbons, acetylene is relatively acidic, though it is still much less acidic than water orethanol. Thus it reacts with strong bases to form acetylide salts. For example, acetylene reacts with sodium amide inliquid ammonia to form sodium acetylide, and with butyllithium in cold THF to give lithium acetylide.

Acetylides of heavy metals are easilyformed by reaction of acetylene withthe metal ions. Several, e.g., silveracetylide (Ag2C2) and copper acetylide

Acetylene 4

(Cu2C2), are powerful and very dangerous explosives.

Reppe chemistryWalter Reppe discovered that in the presence of metal catalysts, acetylene can react to give a wide range ofindustrially significant chemicals. With alcohols, hydrogen cyanide, hydrogen chloride, or carboxylic acids to give vinyl compounds:

With aldehydes to give ethynyl diols, in the Favorskii reaction:

1,4-Butynediol is produced industrially in this way from formaldehyde and acetylene. With carbon monoxide to give acrylic acid, or acrylic esters, which can be used to produce acrylic glass:

Cyclicization to give benzene, cyclooctatetraene, or hydroquinone:

Acetylene 5

WeldingApproximately 20 percent of acetylene is supplied by the industrial gases industry for oxyacetylene gas welding andcutting due to the high temperature of the flame; combustion of acetylene with oxygen produces a flame of over3600K (3300C, 6000F), releasing 11.8kJ/g. Oxyacetylene is the hottest burning common fuel gas. Acetylene isthe third hottest natural chemical flame after dicyanoacetylene's 5260K (4990C, 9010F) and cyanogen at 4798K(4525C, 8180F). Oxy-acetylene welding was a very popular welding process in previous decades; however, thedevelopment and advantages of arc-based welding processes have made oxy-fuel welding nearly extinct for manyapplications. Acetylene usage for welding has dropped significantly. On the other hand, oxy-acetylene weldingequipment is quite versatile not only because the torch is preferred for some sorts of iron or steel welding (as incertain artistic applications), but also because it lends itself easily to brazing, braze-welding, metal heating (forannealing or tempering, bending or forming), the loosening of corroded nuts and bolts, and other applications. BellCanada cable repair technicians still use portable acetylene fueled torch kits as a soldering tool for sealing leadsleeve splices in manholes and in some aerial locations. Oxyacetylene welding may also be used in areas whereelectricity is not readily accessible. As well, oxy-fuel cutting is still very popular and oxy-acetylene cutting isutilized in nearly every metal fabrication shop. For use in welding and cutting, the working pressures must becontrolled by a regulator, since above 15 psi[15] acetylene will decompose explosively into hydrogen and carbon.

Acetylene fuel container/burner as used in the island ofBali

Niche applications

In 1881, the Russian chemist Mikhail Kucherov described thehydration of acetylene to acetaldehyde using catalysts such asmercury(II) bromide. Before the advent of the Wacker process,this reaction was conducted on an industrial scale.

The polymerization of acetylene with Ziegler-Natta catalystsproduces polyacetylene films. Polyacetylene, a chain of CHcentres with alternating single and double bonds, was the one offirst discovered organic semiconductors. Its reaction with iodineproduces a highly electrically conducting material. Although suchmaterials are not useful, these discoveries led to the developmentsof organic semiconductors, as recognized by the Nobel Prize inChemistry in 2000 to Alan J. Heeger, Alan G MacDiarmid, andHideki Shirakawa.

In the early 20th Century acetylene was widely used forillumination, including street lighting in some towns.[16] Mostearly automobiles used carbide lamps before the adoption ofelectric headlights.

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

Acetylene is used to volatilize carbon in radiocarbon dating. The carbonaceous material in an archeological sample istreated with lithium metal in a small specialized research furnace to form lithium carbide (also known as lithiumacetylide). The carbide can then be reacted with water, as usual, to form acetylene gas to be fed into massspectrometer to sort out the isotopic ratio of carbon-14 to carbon-12.

Acetylene 6

Natural occurrenceAcetylene is a moderately common chemical in the universe, often associated with the atmospheres of gas giants.One curious discovery of acetylene is on Enceladus, a moon of Saturn. Natural acetylene is believed to form fromeither catalytic decomposition of long chain hydrocarbons at temperatures of 1,770K and above. Since suchtemperatures are highly unlikely on such a small distant body, this discovery is potentially suggestive of catalyticreactions within that moon, making it a promising site to search for prebiotic chemistry.

Safety and handlingAcetylene is not especially toxic but when generated from calcium carbide it can contain toxic impurities such astraces of phosphine and arsine. It is also highly flammable (hence its use in welding). Its singular hazard isassociated with its intrinsic instability, especially when it is pressurized. Samples of concentrated or pure acetylenecan easily react in an addition-type reaction to form a number of products, typically benzene and/or vinylacetylene.These reactions are exothermic, and unlike other common flammables, do not require oxygen to proceed.Consequently, acetylene can explode with extreme violence if the absolute pressure of the gas exceeds about200kPa (29psi). Most regulators and pressure gauges on equipment report gauge pressure and the safe limit foracetylene therefore is 101 kPagage or 15 psig. It is therefore shipped and stored dissolved in acetone ordimethylformamide (DMF), contained in a gas cylinder with a porous filling (Agamassan), which renders it safe totransport and use, given proper handling. Copper catalyses the decomposition of acetylene and as a result acetyleneshould not be transported in copper pipes. Brass pipe fittings should also be avoided.

Portable lightingCalcium carbide was used to generate acetylene used in the head lamps for miners and cavers before the widespreaduse of incandescent lighting; or many years later low-power/high-lumen LED lighting; and is still used by miningindustries in some nations without workplace safety laws.

References[1] http:/ / www. commonchemistry. org/ ChemicalDetail. aspx?ref=74-86-2[2] http:/ / www. chemspider. com/ Chemical-Structure. 6086. html[3] http:/ / fdasis. nlm. nih. gov/ srs/ srsdirect. jsp?regno=OC7TV75O83[4] http:/ / www. kegg. jp/ entry/ C01548[5] https:/ / www. ebi. ac. uk/ chebi/ searchId. do?chebiId=27518[6] https:/ / www. ebi. ac. uk/ chembldb/ index. php/ compound/ inspect/ CHEMBL116336[7] http:/ / chemapps. stolaf. edu/ jmol/ jmol. php?model=C%23C[8] (http:/ / encyclopedia. airliquide. com/ Encyclopedia. asp?GasID=1#MajorApplications), Gas Encyclopaedia, Air Liquide[9] http:/ / en. wikipedia. org/ w/ index. php?title=Special:ComparePages& rev1=477240406& page2=Acetylene[10][10] R.H.Petrucci, W.S.Harwood and F.G.Herring "General Chemistry", 8th edn.(Prentice-Hall 2002), p.1072[11] Compressed Gas Association (1995) Material Safety and Data Sheet Acetylene (http:/ / www. stoodyind. com/ safety/ msds/ Acetylene.

pdf).[12] Acetylene (http:/ / chestofbooks. com/ crafts/ metal/ Welding-Cutting/ Acetylene. html)[13] Acetylene: How Products are Made (http:/ / science. enotes. com/ how-products-encyclopedia/ acetylene)[14][14] Organic Chemistry 7th ed. by J. McMurry, Thomson 2008[15] http:/ / www. c-f-c. com/ specgas_products/ acetylene. htm[16] The 100 most important chemical compounds: a reference guide (http:/ / books. google. com/ books?id=0AnJU-hralEC)

Acetylene 7

External links Acetylene at Chemistry Comes Alive! (http:/ / jchemed. chem. wisc. edu/ JCESoft/ CCA/ CCA5/ MAIN/

1ORGANIC/ ORG07/ MENU. HTM) 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 (http:/ /

www. youtube. com/ watch?v=KXh7__ri1VQ) Calcium Carbide & Acetylene (http:/ / www. periodicvideos. com/ videos/ mv_calcium_carbide. htm) at The

Periodic Table of Videos (University of Nottingham) CDC - NIOSH Pocket Guide to Chemical Hazards - Acetylene (http:/ / www. cdc. gov/ niosh/ npg/ npgd0008.

html)

Article Sources and Contributors 8

Article Sources and ContributorsAcetylene Source: http://en.wikipedia.org/w/index.php?oldid=600467470 Contributors: 129.128.164.xxx, 1YlGC6dsynvm, A876, ABF, ALD-Holcroft, Aatomic1, AlexAhern, Alfio, Alnokta,AmericanLemming, Andre Engels, Anthony Appleyard, Arkwatem, Atlant, Avanu, AxelBoldt, BD2412, BRW, Baudeagle, Beetstra, Benjah-bmm27, Bennyzc, Bgwhite, Bir el Arweh, Bizzako,Bjornd, Bobblewik, Brian0918, Bryan Derksen, Bunnyhop11, CUSENZA Mario, Cburnett, Ceyockey, Chem-awb, ChemGardener, ChemNerd, Chovain, ChrisGualtieri, Chriswiki,ClockworkSoul, Coga2006, ComaVN, Conversion script, Cornforth, D.c.camero, DA3N, DMacks, DMahalko, Dabby, Daggerstab, Daniel Bonniot de Ruisselet, Danielmiester, DePiep,Deglr6328, Devinh, Dirac66, Discospinster, Double sharp, DrBob, DragonflySixtyseven, Dtgriscom, Dysprosia, Edgar181, Encephalon, Engineman, Epop fr, Eras-mus, Ericg33, EryZ,Euchiasmus, Fedor Babkin, Freestyle-69, Gaius Cornelius, Gene Nygaard, Gentgeen, Geoff Plourde, Ginsuloft, Glane23, Graham87, Grendelkhan, Grim23, Gutsul, Happycool, Hede2000,Helix84, Hellbus, Heron, Hmains, Hodja Nasreddin, Icairns, Itub, J.delanoy, JHunterJ, JZNIOSH, Jaganath, Jamie.parkinson, Jim1138, Jimp, Jleedev, Joeylawn, John125215, John254, Jordgette,Jorge Stolfi, Joshnpowell, Joxy, Jr1942, Juscrooky, Kalamkaar, Knowz, Koyaanis Qatsi, Kragen, Kurykh, L.tak, La goutte de pluie, Landroo, LegacyOfValor, Leuko, Lightmouse, Lightning,LorenzoB, Lugia2453, Luk, Magnus Manske, Marek69, Marenero, Mariushart, MarkSweep, Mathematicks, Memodude, Merovingian, Michall, Miguelfms, Mikespedia, Mikez,Miracleworker5263, Misza13, Mkweise, Molestash, Momo04169.yale, Moogatoo, MrBeck, Mrathi, Munita Prasad, Nairobiny, Nao1958, Nekura, Obradovic Goran, Ohconfucius, OldMoonraker, Oxygenplants, PalestineRemembered, Paulslagle, Peak, Physchim62, PierreAbbat, Pikiwyn, Pinethicket, Pleriche, Popsracer, Printer222, Qqzzccdd, RA0808, Rafael Campos,Renatopub-w01, Rich Farmbrough, Rickjpelleg, Rickproser, Rifleman 82, Rjwilmsi, RobLa, Roberta F., RockMFR, Rolloffle, SCEhardt, Saehrimnir, Sarregouset, Saxbryn, Sburke, Shaddack,Shadowjams, Shalom Yechiel, Shanel, Shootbamboo, Silverchemist, Singhalawap, Skatebiker, Smokefoot, Soliloquial, Spoon!, Srich32977, Srnec, Stassats, Stone, SudlonrA, TK3B07,Tannkrem, Tarquin, Taw, Testem, Thekrazykool809, Thricecube, ThunderSkunk, Tim Starling, Titoxd, Tony1, Trekphiler, Trojancowboy, Trumpet marietta 45750, Tweenk, Tygrrr,Unconcerned, Utsoccerwarrior8, V8rik, VASANTH S.N., VenomSnake, Walkerma, Weregeek, White.matthew.09, Whoop whoop pull up, Wikinaut11, Wmahan, Woohookitty, Worksafe, XiongChiamiov, Yerocus, Yerpo, Yyy, Zephalis, , 315 anonymous edits

Image Sources, Licenses and ContributorsFile:Acetylene-CRC-IR-dimensions-2D.png Source: http://en.wikipedia.org/w/index.php?title=File:Acetylene-CRC-IR-dimensions-2D.png License: Public Domain Contributors: Ben MillsFile:Acetylene-CRC-IR-3D-balls.png Source: http://en.wikipedia.org/w/index.php?title=File:Acetylene-CRC-IR-3D-balls.png License: Public Domain Contributors: Ben MillsFile:Acetylene-3D-vdW.png Source: http://en.wikipedia.org/w/index.php?title=File:Acetylene-3D-vdW.png License: Public Domain Contributors: Benjah-bmm27File:Acetylene-xtal-3D-vdW-111.png Source: http://en.wikipedia.org/w/index.php?title=File:Acetylene-xtal-3D-vdW-111.png License: Public Domain Contributors: Ben MillsFile:Yes check.svg Source: http://en.wikipedia.org/w/index.php?title=File:Yes_check.svg License: Public Domain Contributors: AnomieFile:X mark.svg Source: http://en.wikipedia.org/w/index.php?title=File:X_mark.svg License: Public Domain Contributors: User:GmaxwellFile:LithiumAcetylideFormation.png Source: http://en.wikipedia.org/w/index.php?title=File:LithiumAcetylideFormation.png License: Public Domain Contributors: WalkermaFile:Reppe-chemnistry-vinylization.png Source: http://en.wikipedia.org/w/index.php?title=File:Reppe-chemnistry-vinylization.png License: Creative Commons Attribution-Sharealike 2.5Contributors: en:stoneFile:Reppe-chemistry-endiol.png Source: http://en.wikipedia.org/w/index.php?title=File:Reppe-chemistry-endiol.png License: Creative Commons Attribution-Sharealike 2.5 Contributors:en:stoneFile:Reppe-chemistry-carbonmonoxide-01.png Source: http://en.wikipedia.org/w/index.php?title=File:Reppe-chemistry-carbonmonoxide-01.png License: Creative CommonsAttribution-ShareAlike 3.0 Unported Contributors: Schtone, 1 anonymous editsFile:Reppe-chemistry-carbonmonoxide-02.png Source: http://en.wikipedia.org/w/index.php?title=File:Reppe-chemistry-carbonmonoxide-02.png License: Creative CommonsAttribution-ShareAlike 3.0 Unported Contributors: Deadstar, Karelj, SchtoneFile:Reppe-chemistry-benzene.png Source: http://en.wikipedia.org/w/index.php?title=File:Reppe-chemistry-benzene.png License: Creative Commons Attribution-Sharealike 2.5 Contributors:en:stoneFile:Reppe-chemistry-cyclooctatetraene.png Source: http://en.wikipedia.org/w/index.php?title=File:Reppe-chemistry-cyclooctatetraene.png License: Creative CommonsAttribution-ShareAlike 3.0 Unported Contributors: en:stoneImage:Corrected version of Walter Reppe Hydroquinone synthesis via iron pentacarbonyl under basic conditions.svg Source:http://en.wikipedia.org/w/index.php?title=File:Corrected_version_of_Walter_Reppe_Hydroquinone_synthesis_via_iron_pentacarbonyl_under_basic_conditions.svg License: Creative CommonsAttribution-Sharealike 3.0 Contributors: ThunderSkunkFile:Laskarbit.jpg Source: http://en.wikipedia.org/w/index.php?title=File:Laskarbit.jpg License: Public domain Contributors: User:SreeBot

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AcetyleneDiscoveryPreparationBondingPhysical propertiesChanges of state

OtherReactionsReppe chemistryWeldingNiche applications

Natural occurrenceSafety and handlingPortable lightingReferencesExternal links

License