|Jmol-3D images||Image 1|
|Molar mass||68.07 g/mol|
|Appearance||colorless, volatile liquid|
|S-phrases||S16, S37, S45, S28|
|Flash point||−69 °C|
|Explosive limits||Lower:2.3%, upper:14.3% @ 20 °C|
|LD50||rat > 2g/kg|
|Related compounds||Tetrahydrofuran (THF)
| (what is: / ?)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Furan is a heterocyclic organic compound, consisting of a five-membered aromatic ring with four carbon atoms and one oxygen. The class of compounds containing such rings are also referred to as furans.
Furan is a colorless, flammable, highly volatile liquid with a boiling point close to room temperature. It is soluble in common organic solvents, including alcohol, ether and acetone, but is slightly soluble in water. It is toxic and may be carcinogenic. Furan is used as a starting point to other specialty chemicals.
The name furan comes from the Latin furfur, which means bran. 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.
Health effects and prevalence in the diet 
Furan at a dose of 2 mg/kg body weight (bw) and 4 mg/kg bw has been shown to cause bile duct cancer in rats and liver cancer in mice (National Toxicology Program, 1993; Moser et al. 2009). No long term trials on the adverse effects of furan on human health have been conducted. Furan is found in coffee and in canned and jarred food, including baby food.
In the laboratory, furan can be obtained from furfural by oxidation to furan-2-carboxylic acid, followed by decarboxylation. It can also be prepared directly by thermal decomposition of pentose-containing materials, cellulosic solids especially pine-wood.
Synthesis of furans 
The Feist–Benary synthesis is a classic way to synthesize furans, although many syntheses have been developed. One of the simplest synthesis methods for furans is the reaction of 1,4-diketones with phosphorus pentoxide (P2O5) in the Paal–Knorr synthesis. The thiophene formation reaction of 1,4-diketones with Lawesson's reagent also forms furans as side products. Many routes exist for the synthesis of substituted furans.
Furan is aromatic because one of the lone pairs of electrons on the oxygen atom is 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 bonds. The other lone pair of electrons of the oxygen atom extends in the plane of the flat ring system. The sp2 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.
- 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.
- Furan serves as a diene in Diels-Alder reactions with electron-deficient dienophiles such as ethyl (E)-3-nitroacrylate. The reaction product is a mixture of isomers with preference for the endo isomer:
- Hydrogenation of furans affords sequentially dihydrofurans and tetrahydrofurans.
- In the Achmatowicz reaction, furans converted to dihydropyran compounds.
See also 
- BS 4994 – Furan resin as thermoset FRP for chemical process plant equipments
- Furantetracarboxylic acid
- Simple aromatic rings
- Webster's Online Dictionary
- Hans Dieter Jakubke; Hans Jeschkeit (1994). Concise Encyclopedia of Chemistry. Walter de Gruyter. pp. 001–1201. ISBN 0-89925-457-8.
- H. E. Hoydonckx, W. M. Van Rhijn, W. Van Rhijn, D. E. De Vos, P. A. Jacobs (2005), "Furfural and Derivatives", Ullmann's Encyclopedia of Industrial Chemistry, Weinheim: Wiley-VCH, doi:10.1002/14356007.a12_119.pub2
- Alexander Senning. Elsevier's Dictionary of Chemoetymology. Elsevier, 2006. ISBN 0-444-52239-5.
- Limpricht, H. (1870). "Ueber das Tetraphenol C4H4O". Berichte der deutschen chemischen Gesellschaft 3 (1): pp. 90–91. doi:10.1002/cber.18700030129.
- Rodd, Ernest Harry (1971). Chemistry of Carbon Compounds: A Modern Comprehensive Treatise. Elsevier.
- Wilson, W.C. (1941), "Furan", Org. Synth.; Coll. Vol. 1: 274
- Hou XL, Cheung HY, Hon TY, Kwan PL, Lo TH, Tong SY, Wong HNC (1998). "Regioselective syntheses of substituted furans". Tetrahedron 54 (10): 1955–2020. doi:10.1016/S0040-4020(97)10303-9.
- Katritzky, A. R.; Hur, D.; Kirichenko, K.; Ji, Y.; Steel, P. J.  ARKIVOC, Volume 2004, p. 109 (2004).
- Bruice, Paula Y. (2007). Organic Chemistry (Fifth ed.). Upper Saddle River, NJ: Pearson Prentice Hall. ISBN 0-13-196316-3.
- Masesane I, Batsanov A, Howard J, Modal R, Steel P (2006). "The oxanorbornene approach to 3-hydroxy, 3,4-dihydroxy and 3,4,5-trihydroxy derivatives of 2-aminocyclohexanecarboxylic acid". Beilstein Journal of Organic Chemistry 2 (9): 9. doi:10.1186/1860-5397-2-9. PMC 1524792. PMID 16674802.