Furan
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robot Adding: [[hu:Furán]]
{{Otheruses4|the chemical compound|the river in France|Furan River}}
{{Chembox new
| ImageFile = Furan_chemical_structure.png
| ImageSize = 191px
| IUPACName = Furan
| OtherNames = Oxole, furfuran, divinyl oxide
| Section1 = {{Chembox Identifiers
| CASNo = 110-00-9
| PubChem =
| SMILES = C1=CC=CO1
}}
| Section2 = {{Chembox Properties
| Formula = C<sub>4</sub>H<sub>4</sub>O
| MolarMass = 68.07 g/mol
| Appearance = colorless, volatile liquid
| Density = 0.936 g/mL
| MeltingPt = -85.6 °C
| BoilingPt = 31.4 °C
| Solubility =
}}
| Section3 = {{Chembox Hazards
| MainHazards =
| FlashPt = -35 °C
| Autoignition =
}}
}}
'''Furan''', also known as '''furane''' and '''furfuran''', is a [[Heterocyclic compound|heterocyclic]] [[organic compound]]. It is typically derived by the thermal decomposition of [[pentose]]-containing materials, cellulosic solids especially pine-wood. Furan is a colorless, [[flammable]], highly [[Volatility (chemistry)|volatile]] liquid with a [[boiling point]] close to room temperature. It is [[toxic]] and may be [[carcinogenic]]. Catalytic hydrogenation (see [[redox]]) of furan with a [[palladium]] [[catalyst]] gives [[tetrahydrofuran]].
== History ==
The name ''furan'' comes from the Latin ''furfur'', which means [[bran]].<ref>Alexander Senning. ''Elsevier's Dictionary of Chemoetymology''. Elsevier, '''2006'''. ISBN 0444522395.</ref> The first furan derivative to be described was [[2-furoic acid]], by [[Carl Wilhelm Scheele]] in 1780. Another important derivative, [[furfural]], was reported by [[Johann Wolfgang Döbereiner]] in 1831 and characterised nine years later by [[John Stenhouse]]. Furan itself was first prepared by [[Heinrich Limpricht]] in 1870, although he called it ''tetraphenol''.<ref>{{cite journal | title = Ueber das Tetraphenol C<sub>4</sub>H<sub>4</sub>O | pages = pp. 90–91 | first = H. | last = Limpricht | volume = 3 | issue = 1 | year = 1870 | journal = Berichte der deutschen chemischen Gesellschaft | doi =10.1002/cber.18700030129}}</ref><ref>{{cite book | first = Ernest Harry | last = Rodd | title = Chemistry of Carbon Compounds: A Modern Comprehensive Treatise | publisher = Elsevier | year = 1971}}</ref>
.
==Synthesis and isolation==
*Furan can be obtained from [[furfural]] by oxidation and [[decarboxylation]] of the resulting furan-2-carboxylic acid, the furfural being derived by destructive distillation of corn cobs in the presence of [[sulfuric acid]].<ref>{{OrgSynth | author = Wilson, W.C. | title = Furan | collvol = 1 | collvolpages = 274 | year = 1941 | prep = cv1p0274}}</ref>
*A classic furan [[organic synthesis]] is the [[Feist-Benary synthesis]].
*One of the most simple synthesis methods for furans is the reaction of [[ketone|1,4-diketone]]s with [[phosphorus pentoxide]] (P<sub>2</sub>O<sub>5</sub>) in the [[Paal-Knorr Synthesis]]. It is interesting that the [[thiophene]] formation reaction of 1,4-diketones with [[Lawesson's reagent]] also forms furans as side products.
==Chemistry==
Furan is [[aromatic]] because one of the [[lone pair]]s of [[electron]]s on the oxygen atom is [[delocalized electron|delocalized]] into the ring, creating a 4n+2 aromatic system (see [[Hückel's rule]]) similar to [[benzene]]. Because of the aromaticity, the molecule is flat and lacks discrete [[double bond]]s. The other lone pair of electrons of the oxygen atom extends in the plane of the flat ring system. The [[Orbital hybridisation|sp<sup>2</sup> hybridization]] is to allow one of the lone pairs of oxygen to reside in a [[p orbital]] and thus allow it to interact within the pi-system.
Due to its aromaticity, furan's behavior is quite dissimilar to that of the more typical heterocyclic [[ether]]s such as [[THF|tetrahydrofuran]].
*It is considerably more reactive than [[benzene]] in [[electrophilic substitution]] reactions, due to the electron-donating effects of the oxygen heteroatom. Examination of the resonance contributors shows the increased electron density of the ring, leading to increased rates of electrophilic substitution<ref>{{cite book |title=Organic Chemistry, Fifth Edition |last=Bruice |first=Paula Y. |year=2007 |publisher=Pearson Prentice Hall |location=Upper Saddle River, NJ |isbn=0-13-196316-3}}</ref>.
[[Image:Furan Resonance.png|850px|Resonance contributors of furan]]
* Furan serves as a [[diene]] in [[Diels-Alder reaction]]s with electron-deficient [[dienophile]]s such as ethyl (E)-3-nitroacrylate.<ref>{{cite journal | title = The oxanorbornene approach to 3-hydroxy, 3,4-dihydroxy and 3,4,5-trihydroxy derivatives of 2-aminocyclohexanecarboxylic acid | author = Masesane I, Batsanov A, Howard J, Modal R, Steel P | journal = [[Beilstein Journal of Organic Chemistry]] | year = 2006 | volume = 2 | issue = 9 | doi = 10.1186/1860-5397-2-9 | pages = 9 | pmid = 16674802}}</ref> The reaction product is a mixture of isomers with preference for the [[endo isomer]]:
:[[Image:Furan cycloaddition.png|500px|Furan Diels-Alder reaction with ethyl (E)-3-nitroacrylate]]
* [[Hydrogenation]] of furans affords sequentially dihydrofurans and [[tetrahydrofuran]]s.
* In the [[Achmatowicz reaction]], furans converted to dihydropyran compounds.
== See also ==
* [[2,5-Dimethylfuran]], a furan derivative that may be a possible [[biofuel]]
* [[Tetrahydrofuran]] (THF), the fully [[hydrogenation|hydrogenated]] analog of furan and a common [[solvent]].
* [[Pyrrole]], the [[nitrogen]] analog of furan.
* [[Thiophene]], the [[sulfur]] analog of furan.
* [[Selenophene]], the [[selenium]] analog of furan.
* [[Tellurophene]], the [[tellurium]] analog of furan.
* [[Benzofuran]], furan with a fused benzene ring.
* [[Dibenzofuran]], a compound class similar to dibenzo[[dioxin]]s.
* [[Simple aromatic ring]]s
* [[Furanose]]
== References ==
{{reflist}}
== External links ==
*[http://www.compchemwiki.org/index.php?title=Furan Furan on Computational Chemistry Wiki]
*[http://www.organic-chemistry.org/synthesis/heterocycles/furans/furans.shtm Recent synthetic methods]
[[Category:Furans|*]]
[[Category:Oxygen heterocycles]]
[[Category:Aromatic compounds]]
[[Category:Heterocyclic compounds]]
[[Category:Simple aromatic rings]]
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