furan furan furan is a heterocyclic organic compound, consisting of a five-membered aromatic ring with four carbon atoms and one oxygen atom. chemical compounds containing such rings are also referred to as furans. furan full structural formula of furan skeletal formula showing numbering convention ball-and-stick model space-filling model names preferred iupac name furan systematic iupac name 1,4-epoxybuta-1,3-diene1-oxacyclopenta-2,4-diene other names oxoleoxaannulene1,4-epoxy-1,3-butadiene5-oxacyclopenta-1,3-diene5-oxacyclo-1,3-pentadienefurfurandivinylene oxide identifiers cas number 110-00-9 y 3d model (jsmol) interactive image beilstein reference 103221 chebi chebi:35559 y chembl chembl278980 y chemspider 7738 y echa infocard 100.003.390 ec number 203-727-3 gmelin reference 25716 kegg c14275 y pubchem cid 8029 rtecs number lt8524000 unii uc0xv6a8n9 y un number 2389 comptox dashboard (epa) dtxsid6020646 inchi inchi=1s/c4h4o/c1-2-4-5-3-1/h1-4h ykey: ylqbmqcuizjeeh-uhfffaoysa-n yinchi=1/c4h4o/c1-2-4-5-3-1/h1-4hkey: ylqbmqcuizjeeh-uhfffaoyac smiles c1ccoc1 properties chemical formula c4h4o molar mass 68.075 g·mol−1 appearance colorless, volatile liquid density 0.936 g/ml melting point −85.6 °c (−122.1 °f; 187.6 k) boiling point 31.3 °c (88.3 °f; 304.4 k) magnetic susceptibility (χ) -43.09·10−6 cm3/mol hazards ghs labelling: pictograms signal word danger hazard statements h224, h302, h315, h332, h341, h350, h373, h412 precautionary statements p201, p202, p210, p233, p240, p241, p242, p243, p260, p261, p264, p270, p271, p273, p280, p281, p301+p312, p302+p352, p303+p361+p353, p304+p312, p304+p340, p308+p313, p312, p314, p321, p330, p332+p313, p362, p370+p378, p403+p235, p405, p501 nfpa 704 (fire diamond) 3 4 1 flash point −36 °c (−33 °f; 237 k) autoignitiontemperature 390 °c (734 °f; 663 k) explosive limits lower: 2.3%upper: 14.3% at 20 °c lethal dose or concentration (ld, lc): ld50 (median dose) > 2 g/kg (rat) safety data sheet (sds) pennakem related compounds related heterocycles pyrrolethiophene related compounds tetrahydrofuran (thf)2,5-dimethylfuranbenzofurandibenzofuran structure point group c2v except where otherwise noted, data are given for materials in their standard state (at 25 °c , 100 kpa). y verify (what is yn ?) infobox references 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, and is slightly soluble in water. its odor is "strong, ethereal; chloroform-like". it is toxic and may be carcinogenic in humans. furan is used as a starting point for other speciality chemicals. history the name "furan" comes from the latin furfur, which means bran. (furfural is produced from 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" (as if it were a four-carbon analog to phenol, c6h5oh). production industrially, furan is manufactured by the palladium-catalyzed decarbonylation of furfural, or by the copper-catalyzed oxidation of 1,3-butadiene: in the laboratory, furan can be obtained from furfural by oxidation to 2-furoic acid, followed by decarboxylation. it can also be prepared directly by thermal decomposition of pentose-containing materials, and 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. chemistry 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 π system. due to its aromaticity, furan's behavior is quite dissimilar to that of the more typical heterocyclic ethers such as 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. 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: diels-alder reaction of furan with arynes provides corresponding derivatives of dihydronaphthalenes, which are useful intermediates in synthesis of other polycyclic aromatic compounds. hydrogenation of furans sequentially affords dihydrofurans and tetrahydrofurans. in the achmatowicz reaction, furans are converted to dihydropyran compounds. pyrrole can be prepared industrially by reacting furan and ammonia in the presence of solid acid catalysts, such as sio2 and al2o3. safety furan is found in heat-treated commercial foods and is produced through thermal degradation of natural food constituents. it can be found in roasted coffee, instant coffee, and processed baby foods. research has indicated that coffee made in espresso makers and coffee made from capsules contain more furan than that made in traditional drip coffee makers, although the levels are still within safe health limits. exposure to furan at doses about 2,000 times the projected level of human exposure from foods increases the risk of hepatocellular tumors in rats and mice and bile duct tumors in rats. furan is therefore listed as a possible human carcinogen.