Names | |||
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Preferred IUPAC name Furan [1] | |||
Systematic IUPAC name 1,4-Epoxybuta-1,3-diene 1-Oxacyclopenta-2,4-diene | |||
Other names Oxole Oxa[5]annulene 1,4-Epoxy-1,3-butadiene 5-Oxacyclopenta-1,3-diene 5-Oxacyclo-1,3-pentadiene Furfuran Divinylene oxide | |||
Identifiers | |||
3D model (JSmol) | |||
103221 | |||
ChEBI | |||
ChEMBL | |||
ChemSpider | |||
ECHA InfoCard | 100.003.390 | ||
EC Number |
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25716 | |||
KEGG | |||
PubChem CID | |||
RTECS number |
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UNII | |||
UN number | 2389 | ||
CompTox Dashboard (EPA) | |||
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Properties | |||
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) | ||
-43.09·10−6 cm3/mol | |||
Hazards | |||
GHS labelling: | |||
Danger | |||
H224, H302, H315, H332, H341, H350, H373, H412 | |||
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) | |||
Flash point | −36 °C (−33 °F; 237 K) | ||
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 | Pyrrole Thiophene | ||
Related compounds | Tetrahydrofuran (THF) 2,5-Dimethylfuran Benzofuran Dibenzofuran | ||
Structure | |||
C2v | |||
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). |
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 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. [2] Its odor is "strong, ethereal; chloroform-like". [3] It is toxic and may be carcinogenic in humans. Furan is used as a starting point for other speciality chemicals. [4]
The name "furan" comes from the Latin furfur, which means bran [5] (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). [6] [7]
Industrially, furan is manufactured by the palladium-catalyzed decarbonylation of furfural, or by the copper-catalyzed oxidation of 1,3-butadiene: [4]
In the laboratory, furan can be obtained from furfural by oxidation to 2-furoic acid, followed by decarboxylation. [8] It can also be prepared directly by thermal decomposition of pentose-containing materials, and cellulosic solids, especially pine wood.
The Feist–Benary synthesis is a classic way to synthesize furans. The reaction involves alkylation of 1,3-diketones with α-bromoketones followed by dehydration of an intermediate hydroxydihydrofuran. [9] The other traditional route involve the reaction of 1,4-diketones with phosphorus pentoxide (P2O5) in the Paal–Knorr synthesis. [10]
Many routes exist for the synthesis of substituted furans. [11] [12]
Furan has aromatic character 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). The aromaticity is modest relative to that for benzene and related heterocycles thiophene and pyrrole. The resonance energies of benzene, pyrrole, thiophene, and furan are, respectively, 152, 88, 121, and 67 kJ/mol (36, 21, 29, and 16 kcal/mol). Thus, these heterocycles, especially furan, are far less aromatic than benzene, as is manifested in the lability of these rings. [13] The molecule is flat but the C=C groups attached to oxygen retain significant double bond character. The other lone pair of electrons of the oxygen atom extends in the plane of the flat ring system.
Examination of the resonance contributors shows the increased electron density of the ring, leading to increased rates of electrophilic substitution. [14]
Because of its partial aromatic character, furan's behavior is intermediate between that of an enol ether and an aromatic ring. It is dissimilar vs ethers such as tetrahydrofuran.
Like enol ethers, 2,5-disubstituted furans are susceptible to hydrolysis to reversibly give 1,4-diketones.
Furan serves as a diene in Diels–Alder reactions with electron-deficient dienophiles such as ethyl (E)-3-nitroacrylate. [15] 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. [16]
Furan is found in heat-treated commercial foods and is produced through thermal degradation of natural food constituents. [18] [19] It can be found in roasted coffee, instant coffee, and processed baby foods. [19] [20] [21] 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. [22]
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. [23] Furan is therefore listed as a possible human carcinogen. [23]
Aromatic compounds, also known as "mono- and polycyclic aromatic hydrocarbons", are organic compounds containing one or more aromatic rings. The word "aromatic" originates from the past grouping of molecules based on odor, before their general chemical properties were understood. The current definition of aromatic compounds does not have any relation with their odor.
A heterocyclic compound or ring structure is a cyclic compound that has atoms of at least two different elements as members of its ring(s). Heterocyclic organic chemistry is the branch of organic chemistry dealing with the synthesis, properties, and applications of organic heterocycles.
Pyridine is a basic heterocyclic organic compound with the chemical formula C5H5N. It is structurally related to benzene, with one methine group (=CH−) replaced by a nitrogen atom. It is a highly flammable, weakly alkaline, water-miscible liquid with a distinctive, unpleasant fish-like smell. Pyridine is colorless, but older or impure samples can appear yellow, due to the formation of extended, unsaturated polymeric chains, which show significant electrical conductivity. The pyridine ring occurs in many important compounds, including agrochemicals, pharmaceuticals, and vitamins. Historically, pyridine was produced from coal tar. As of 2016, it is synthesized on the scale of about 20,000 tons per year worldwide.
Pyrrole is a heterocyclic, aromatic, organic compound, a five-membered ring with the formula C4H4NH. It is a colorless volatile liquid that darkens readily upon exposure to air. Substituted derivatives are also called pyrroles, e.g., N-methylpyrrole, C4H4NCH3. Porphobilinogen, a trisubstituted pyrrole, is the biosynthetic precursor to many natural products such as heme.
In chemistry, aromaticity means a molecule has a cyclic (ring-shaped) structure with pi bonds in resonance. Aromatic rings give increased stability compared to saturated compounds having single bonds, and other geometric or connective non-cyclic arrangements with the same set of atoms. Aromatic rings are very stable and do not break apart easily. Organic compounds that are not aromatic are classified as aliphatic compounds—they might be cyclic, but only aromatic rings have enhanced stability. The term aromaticity with this meaning is historically related to the concept of having an aroma, but is a property distinct from that meaning.
The Friedel–Crafts reactions are a set of reactions developed by Charles Friedel and James Crafts in 1877 to attach substituents to an aromatic ring. Friedel–Crafts reactions are of two main types: alkylation reactions and acylation reactions. Both proceed by electrophilic aromatic substitution.
In organic chemistry, a dicarbonyl is a molecule containing two carbonyl groups. Although this term could refer to any organic compound containing two carbonyl groups, it is used more specifically to describe molecules in which both carbonyls are in close enough proximity that their reactivity is changed, such as 1,2-, 1,3-, and 1,4-dicarbonyls. Their properties often differ from those of monocarbonyls, and so they are usually considered functional groups of their own. These compounds can have symmetrical or unsymmetrical substituents on each carbonyl, and may also be functionally symmetrical or unsymmetrical.
Thiophene is a heterocyclic compound with the formula C4H4S. Consisting of a planar five-membered ring, it is aromatic as indicated by its extensive substitution reactions. It is a colorless liquid with a benzene-like odor. In most of its reactions, it resembles benzene. Compounds analogous to thiophene include furan (C4H4O), selenophene (C4H4Se) and pyrrole (C4H4NH), which each vary by the heteroatom in the ring.
Phenanthrene is a polycyclic aromatic hydrocarbon (PAH) with formula C14H10, consisting of three fused benzene rings. It is a colorless, crystal-like solid, but can also appear yellow. Phenanthrene is used to make dyes, plastics and pesticides, explosives and drugs. It has also been used to make bile acids, cholesterol and steroids.
In organic chemistry, an aryl halide is an aromatic compound in which one or more hydrogen atoms, directly bonded to an aromatic ring are replaced by a halide. The haloarene are different from haloalkanes because they exhibit many differences in methods of preparation and properties. The most important members are the aryl chlorides, but the class of compounds is so broad that there are many derivatives and applications.
In organic chemistry, nitration is a general class of chemical processes for the introduction of a nitro group into an organic compound. The term also is applied incorrectly to the different process of forming nitrate esters between alcohols and nitric acid. The difference between the resulting molecular structures of nitro compounds and nitrates is that the nitrogen atom in nitro compounds is directly bonded to a non-oxygen atom, whereas in nitrate esters, the nitrogen is bonded to an oxygen atom that in turn usually is bonded to a carbon atom.
Benzofuran is the heterocyclic compound consisting of fused benzene and furan rings. This colourless liquid is a component of coal tar. Benzofuran is the "parent" of many related compounds with more complex structures. For example, psoralen is a benzofuran derivative that occurs in several plants.
Isoxazole is an electron-rich azole with an oxygen atom next to the nitrogen. It is also the class of compounds containing this ring. Isoxazolyl is the univalent radical derived from isoxazole.
Anisole, or methoxybenzene, is an organic compound with the formula CH3OC6H5. It is a colorless liquid with a smell reminiscent of anise seed, and in fact many of its derivatives are found in natural and artificial fragrances. The compound is mainly made synthetically and is a precursor to other synthetic compounds. Structurally, it is an ether with a methyl and phenyl group attached. Anisole is a standard reagent of both practical and pedagogical value.
The Dakin oxidation (or Dakin reaction) is an organic redox reaction in which an ortho- or para-hydroxylated phenyl aldehyde (2-hydroxybenzaldehyde or 4-hydroxybenzaldehyde) or ketone reacts with hydrogen peroxide (H2O2) in base to form a benzenediol and a carboxylate. Overall, the carbonyl group is oxidised, whereas the H2O2 is reduced.
The Blanc chloromethylation is the chemical reaction of aromatic rings with formaldehyde and hydrogen chloride to form chloromethyl arenes. The reaction is catalyzed by Lewis acids such as zinc chloride. The reaction was discovered by Gustave Louis Blanc (1872-1927) in 1923
In organic chemistry, the Paal–Knorr Synthesis is a reaction used to synthesize substituted furans, pyrroles, or thiophenes from 1,4-diketones. It is a synthetically valuable method for obtaining substituted furans and pyrroles, which are common structural components of many natural products. It was initially reported independently by German chemists Carl Paal and Ludwig Knorr in 1884 as a method for the preparation of furans, and has been adapted for pyrroles and thiophenes. Although the Paal–Knorr synthesis has seen widespread use, the mechanism wasn't fully understood until it was elucidated by V. Amarnath et al. in the 1990s.
A carbon–oxygen bond is a polar covalent bond between atoms of carbon and oxygen. Carbon–oxygen bonds are found in many inorganic compounds such as carbon oxides and oxohalides, carbonates and metal carbonyls, and in organic compounds such as alcohols, ethers, carbonyl compounds and oxalates. Oxygen has 6 valence electrons of its own and tends to fill its outer shell with 8 electrons by sharing electrons with other atoms to form covalent bonds, accepting electrons to form an anion, or a combination of the two. In neutral compounds, an oxygen atom can form up to two single bonds or one double bond with carbon, while a carbon atom can form up to four single bonds or two double bonds with oxygen.
Indole is an aromatic, heterocyclic, organic compound with the formula C8H7N. It has a bicyclic structure, consisting of a six-membered benzene ring fused to a five-membered pyrrole ring. Indole is widely distributed in the natural environment and can be produced by a variety of bacteria. As an intercellular signal molecule, indole regulates various aspects of bacterial physiology, including spore formation, plasmid stability, resistance to drugs, biofilm formation, and virulence. The amino acid tryptophan is an indole derivative and the precursor of the neurotransmitter serotonin.
Electrophilic aromatic substitution is an organic reaction in which an atom that is attached to an aromatic system is replaced by an electrophile. Some of the most important electrophilic aromatic substitutions are aromatic nitration, aromatic halogenation, aromatic sulfonation, alkylation and acylation Friedel–Crafts reaction.
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