Thiophene 508777 220740779 2008-06-21T10:28:03Z DOI bot 6652755 Citation maintenance. You can [[WP:DOI|use this bot]] yourself! Please [[User:DOI_bot/bugs|report any bugs]]. {{Chembox new | Name = Thiophene | ImageFile = Thiophene chemical structure.png | ImageSize = 200px | ImageName = Thiophene | IUPACName = Thiophene | OtherNames = Thiofuran<br />Thiacyclopentadiene | Section1 = {{Chembox Identifiers | SMILES = C1=CC=CS1 | PubChem = 8030 | CASNo = 110-02-1 | RTECS = XM7350000 }} | Section2 = {{Chembox Properties | Formula = C<sub>4</sub>H<sub>4</sub>S | MolarMass = 84.14 g/mol | Appearance = colorless liquid | Density = 1.051 g/ml, liquid | MeltingPt = −38 °C | BoilingPt = 84 °C | Viscosity = 8.712 c[[Poise|P]] at 0.2 °C<br/>6.432 c[[Poise|P]] at 22.4 °C | RefractIndex = 1.5287 }} | Section3 = {{Chembox Structure | Dipole = }} | Section7 = {{Chembox Hazards | ExternalMSDS = [http://physchem.ox.ac.uk/MSDS/TH/thiophene.html External MSDS] | EUClass = not listed | NFPA-H = 2 | NFPA-F = 3 | NFPA-R = | FlashPt = −1 °C }} | Section8 = {{Chembox Related | Function = [[thioether]]s | OtherFunctn = [[Tetrahydrothiophene]]<br />[[Diethyl sulfide]] | OtherCpds = [[Furan]]<br />[[Pyrrole]] }} }} '''Thiophene''' is the [[heterocyclic]] compound with the formula C<sub>4</sub>H<sub>4</sub>S. Consisting of a five-membered ring, it is [[aromaticity|aromatic]] as indicated by its extensive substitution reactions. Related to thiophene are [[benzothiophene]] and dibenzothiophene, containing the thiophene ring fused with one and two benzene rings, respectively. Compounds analogous to thiophene include [[furan]] (C<sub>4</sub>H<sub>4</sub>O) and [[pyrrole]] (C<sub>4</sub>H<sub>4</sub>NH). ==Isolation, occurrence== Thiophene was discovered as a contaminant in benzene.<ref>{{cite journal | author= Viktor Meyer | title = Ueber den Begleiter des Benzols im Steinkohlenteer | journal = [[Berichte der Deutschen chemischen Gesellschaft]] | year = 1883 | volume = 16 | issue = | pages = 1465–1478 | url = http://gallica.bnf.fr/ark:/12148/bpt6k90696b/f1470.chemindefer | doi = 10.1002/cber.188301601324}}</ref> It was observed that [[isatin]] forms a blue dye if it is mixed with [[sulfuric acid]] and crude [[benzene]]. The formation of the blue indophenin was long believed to be a reaction with benzene. [[Victor Meyer]] was able to isolate the substance resposible for this reaction from benzene. This new heterocyclic compound was thiophene.<ref>{{cite journal | author= Ward C. Sumpter | title = The Chemistry of Isatin | journal = [[Chemical Reviews]] | year = 1944 | volume = 34, | issue = 3 | pages = 393–434 | doi = 10.1021/cr60109a003}}</ref> Thiophene and its derivatives occur in [[petroleum]], sometimes in concentrations up to 1-3%. The thiophenic content of [[Petroleum|oil]] and [[coal]] is removed via the [[hydrodesulfurization]] (HDS) process. In HDS, the liquid or gaseous feed is passed over a form of [[molybdenum disulfide]] catalyst under a pressure of H<sub>2</sub>. Thiophenes undergo hydrogenolysis to form [[hydrocarbons]] and [[hydrogen sulfide]]. Thus, thiophene itself is converted to butane and H<sub>2</sub>S. More prevalent and more problematic in petroleum are [[benzothiophene]] and dibenzothiophene. ==Synthesis and production== Reflecting their high stabilities, thiophenes arise from many reactions involving sulfur sources and hydrocarbons, especially unsaturated ones, e.g. acetylenes and elemental sulfur, which was the first synthesis of thiophene by Viktor Meyer in the year of its discovery. Thiophenes are classically prepared by the reaction of 1,4-di[[ketone]]s, diesters, or dicarboxylates with sulfiding reagents such as P<sub>4</sub>S<sub>10</sub>. Specialized thiophenes can be synthesized similarly using or [[Lawesson's reagent]] as the sulfiding agent, via the [[Gewald reaction]], which involves the condensation of two [[esters]] in the presence of elemental sulfur. Another method is the [[Volhard-Erdmann cyclization]]. Thiophene is produced on a scale of ca. 2M kg per year worldwide. Production involves the vapor phase reaction of a sulfur source, typically [[carbon disulfide]], and [[butanol]]. These reagents are contacted with an oxide catalyst at 500-550 °C.<ref name=Ullmann>Jonathan Swanston “Thiophene” in Ullmann’s Encyclopedia of Industrial Chemistry Wiley-VCH, Weinheim, 2006. {{DOI|10.1002/14356007.a26 793.pub2}}.</ref> ==Properties== At room temperature, thiophene is a colorless liquid with a mildly pleasant odor reminiscent of [[benzene]], with which thiophene shares some similarities. The high reactivity of thiophene toward sulfonation is the basis for the separation of thiophene from benzene, which are difficult to separate by [[distillation]] due to their similar boiling points (4 °C difference at ambient pressure). Like benzene, thiophene forms an [[azeotrope]] with water. ==Reactivity== Thiophene is considered aromatic, although theoretical calculations suggest that the degree of aromaticity is less than that of benzene. The "electron pairs" on sulfur are significantly [[delocalized]] in the [[pi electron]] system. As a consequence of its aromaticity, thiophene does not exhibit the properties seen for conventional [[thioether]]s. For example the sulfur atom resists alkylation and oxidation. ===Toward electrophiles=== Although the sulfur atom is relatively unreactive, the flanking carbon centers, the 2- and 5-positions, are highly susceptible to attack by [[electrophile]]s. Halogens give initially 2-halo derivatives followed by 2,5-dihalothiophenes; perhalogenation is easily accomplished to give C<sub>4</sub>X<sub>4</sub>S (X = Cl, Br, I).<ref>{{OrgSynth | author = Henry Y. Lew and C. R. Noller| title = 2-Iodolthiophene| collvol = 4 | collvolpages = 545 | year = 1963 | prep = CV4P0545}}</ref> Thiophene brominates 10<sup>7</sup> times faster than does benzene.<ref name=Ullmann/> Chloromethylation and chloroethylation occur readily at the 2,5-positions. Reduction of the chloromethyl product gives 2-methylthiophene. Hydrolysis followed by dehydration of the chloroethyl species gives 2-vinylthiophene.<ref>{{OrgSynth | author = W. S. Emerson and T. M. Patrick, Jr.| title = 2-Vinylthiophene| collvol = 4 | collvolpages = 980 | year = 1963 | prep = CV4P0980}}</ref><ref>{{OrgSynth | author = K. B. Wiberg and H. F. McShane| title = 2-Chloromethylthiophene| collvol = 3 | collvolpages = 1 | year = 1955 | prep = CV3P0197}}</ref> ===Desulfurization by Raney Nickel=== Desulfurization of thiophene with [[Raney nickel]] affords butane. When coupled with the easy 2,5-difunctionalization of thiophene, desulfurization provides a route to 1,4-disubstituted butanes. ===Lithiation=== Not only is thiophene reactive toward electrophiles, it is also readily lithiated with [[butyl lithium]] to give 2-lithiothiophene, which is a precursor to a variety of derivatives, including dithienyl.<ref>{{OrgSynth | author = E. Jones and I. M. Moodie | title = 2-Thiophenethiol| collvol = 6 | collvolpages = 979| year = 1988 | prep = CV6P0979}}</ref> ===Coordination chemistry=== Thiophene exhibits little thioether-like character, but it does serve as a pi-ligand forming [[sandwhich complex|piano-stool]] complexes such as Cr(η<sup>5</sup>-C<sub>4</sub>H<sub>4</sub>S)(CO)<sub>3</sub>.<ref>Rauchfuss, T. B., "The Coordination Chemistry of Thiophenes", Progress in Inorganic Chemistry 1991, volume 39, pp. 259-311. ISBN: 978-0-471-54489-0</ref> ==Uses== Thiophenes are important heterocyclic compounds that are widely used as building blocks in many agrochemicals and pharmaceuticals.<ref name=Ullmann/> The benzene ring of a biologically active compound may often be replaced by a thiophene without loss of activity.<ref name=Lednicer1999>{{cite book | author = Daniel Lednicer | title = The Organic Chemistry of Drug Synthesis | publisher = Wiley Interscience | volume = 6 | date = 1999 | location = New York | pages = 187 | id = ISBN 0-471-24510-0 }}</ref> This is seen in examples such as the [[Non-steroidal anti-inflammatory drug|NSAID]] [[lornoxicam]], the thiophene analog of [[piroxicam]]. ===Polythiophene=== The polymer formed by linking thiophene through its 2,5 positions is called [[polythiophene]]. Polythiophene itself has poor processing properties. More useful are polymers derived from thiophenes substituted at the 3- and 3- and 4- positions. Polythiophenes become electrically conductive upon partial oxidation, i.e. they become "organic metals."<ref>{{cite journal | author = J. Roncali | title = Conjugated poly(thiophenes): synthesis, functionalization, and applications | year = 1992 | journal = [[Chem. Rev.]] | volume = 92 | issue = 4 | pages = 711–738 | doi = 10.1021/cr00012a009}}</ref> ==References== <!-- How to add a footnote: NOTE: Footnotes in this article use names, not numbers. Please see [[Wikipedia:Footnotes]] for details. 1) Assign your footnote a unique name, for example TheSun_Dec9. 2) Add the macro{{ref|TheSun_Dec9}} to the body of the article, where you want the new footnote. 3) Take note of the name of the footnote that immediately precedes yours in the article body. 4) Add #{{Note|TheSun_Dec9}} to the footnote numbered-list, immediately below the footnote you noted in step 3. 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