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Benzene from Wikipedia, the Free Encyclopedia See Also: Benzole Benzene From Wikipedia, the free encyclopedia See also: Benzole Benzene is an organic chemical compound with Benzene the molecular formula C6H6. Its molecule is composed of 6 carbon atoms joined in a ring, with 1 hydrogen atom attached to each carbon atom. Because its molecules contain only carbon and hydrogen atoms, benzene is classed as a hydrocarbon. Benzene is a natural constituent of crude oil, and is one of the most elementary petrochemicals. Benzene is an aromatic hydrocarbon and the second [n]-annulene ([6]-annulene), a cyclic hydrocarbon with a continuous pi bond. It is sometimes abbreviated Ph–H. Benzene is a colorless and highly flammable liquid with a sweet smell. It is mainly used as a precursor to heavy chemicals, such as ethylbenzene and cumene, which are produced on a billion kilogram scale. Because it has a high octane number, it is an important component of gasoline, composing a few percent of its mass. Most non-industrial applications have been limited by benzene's carcinogenicity. IUPAC name Contents benzene 1 History Systematic name 1.1 Discovery 1.2 Ring formula cyclohexa-1,3,5-triene 1.3 Early applications Other names 2 Structure 3 Benzene derivatives 1,3,5-cyclohexatriene 4 Production benzol 4.1 Catalytic reforming phene 4.2 Toluene hydrodealkylation 4.3 Toluene disproportionation Identifiers 4.4 Steam cracking CAS number 71-43-2 4.5 Other sources PubChem 241 5 Uses ChemSpider 236 5.1 Component of gasoline 6 Reactions UNII J64922108F 6.1 Sulfonation, chlorination, nitration EC number 200-753-7 6.2 Hydrogenation KEGG C01407 6.3 Metal complexes ChEBI CHEBI:16716 7 Health effects ChEMBL CHEMBL277500 8 Exposure to benzene 8.1 Inhalation RTECS number CY1400000 8.2 Exposure through smoking Jmol-3D images Image 1 8.3 Exposure from soft drinks (http://chemapps.stolaf.edu/jmol/jmol.php? 8.4 Case examples model=c1ccccc1) 8.5 Benzene exposure limits SMILES 8.6 Exposure monitoring InChI 8.7 Biomarkers of exposure 8.8 Biotransformations Properties 8.9 Molecular toxicology Molecular formula C6H6 8.10 Biological oxidation and Molar mass 78.11 g mol−1 carcinogenic activity Appearance Colorless liquid 8.11 Summary Odor aromatic, gasoline-like 9 See also 3[1] 10 References Density 0.8765(20) g/cm 11 External links Melting point 5.5 °C, 278.7 K, 41.9 °F Boiling point History 80.1 °C, 353.3 K, 176.18 °F Solubility in water 1.79 g/L (15 °C)[2][3][4] Discovery Solubility soluble in alcohol, chloroform, CCl4, diethyl ether, acetone The word "benzene" derives historically from "gum benzoin", sometimes called "benjamin" (i.e., benzoin log P 2.13 resin), an aromatic resin known to European Vapor pressure 10 kPa pharmacists and perfumers since the 15th century λmax 255 nm [5] as a product of southeast Asia. An acidic Magnetic 54.8 x 10−6 cm3/mol material was derived from benzoin by sublimation, susceptibility and named "flowers of benzoin", or benzoic acid. The hydrocarbon derived from benzoic acid thus Refractive index 1.50108 acquired the name benzin, benzol, or benzene.[6] (nD) Viscosity 0.652 cP at 20 °C Michael Faraday first isolated and identified Dipole moment 0 D benzene in 1825 from the oily residue derived from the production of illuminating gas, giving it the name Thermochemistry bicarburet of hydrogen.[7][8] Std enthalpy of 48.7 kJ/mol o formation ΔfH 298 In 1833, Eilhard Mitscherlich produced it via the Standard molar 173.26 J/K mol distillation of benzoic acid (from gum benzoin) and o entropy S 298 lime. He gave the compound the name benzin.[9] Specific heat 136.0 J/K mol capacity, C In 1836, the French chemist Auguste Laurent Hazards [10] named the substance "phène"; this is the root of MSDS External MSDS the word phenol, which is hydroxylated benzene, EU classification Flammable (F) and phenyl, which is the radical formed by Carc. Cat. 1 abstraction of a hydrogen atom (free radical H•) from benzene. Muta. Cat. 2 Toxic (T) In 1845, Charles Mansfield, working under August R-phrases R45, R46, R11, R16, Wilhelm von Hofmann, isolated benzene from coal R36/38,R48/23/24/25, R65 tar.[12] Four years later, Mansfield began the first S-phrases S53, S45 industrial-scale production of benzene, based on the coal-tar method.[13][14] Gradually the sense NFPA 704 3 developed among chemists that substances related 2 0 to benzene represent a diverse chemical family. In 1855 August Wilhelm Hofmann used the word "aromatic" to designate this family relationship, after Flash point −11.63 °C, 262 K a characteristic property of many of its Autoignition 497.78 °C (770.93 K) members.[15] temperature Ring formula Explosive limits 1.2–7.8% LD50 930 mg/kg (rat, oral) The empirical formula for benzene was long known, Related compounds but its highly polyunsaturated structure, with just Related compounds toluene one hydrogen atom for each carbon atom, was borazine challenging to determine. Archibald Scott Couper in 1858 and Joseph Loschmidt in 1861[16] Supplementary data page suggested possible structures that contained Structure and n, εr, etc. multiple double bonds or multiple rings, but too little properties evidence was then available to help chemists decide Thermodynamic Phase behaviour on any particular structure. data Solid, liquid, gas In 1865, the German chemist Friedrich August Spectral data UV, IR, NMR, MS Kekulé published a paper in French (for he was (verify) (what is: / ?) then teaching in Francophone Belgium) suggesting Except where noted otherwise, data are given for materials in that the structure contained a six-membered ring of their standard state (at 25 °C, 100 kPa) carbon atoms with alternating single and double bonds. The next year he published a much longer Infobox references paper in German on the same subject.[17][18] Kekulé used evidence that had accumulated in the intervening years— namely, that there always appeared to be only one isomer of any monoderivative of benzene, and that there always appeared to be exactly three isomers of every derivative— now understood to correspond to the ortho, meta, and para Historic benzene formulae as proposed by patterns of arene substitution—to argue in support of his [19] Kekulé.[11] proposed structure. Kekulé's symmetrical ring could explain these curious facts, as well as benzene's 1:1 carbon- hydrogen ratio.[20] The new Historic benzene formulae (from left to right) by Claus (1867),[21] Dewar (1867),[22] Ladenburg (1869),[23] Armstrong (1887),[24] Thiele (1899)[25] and Kekulé (1865). Dewar benzene and prismane are different chemicals that have Dewar's and Ladenburg's structures. Thiele and Kekulé's structures are used today. understanding of benzene, and hence of all aromatic compounds, proved to be so important for both pure and applied chemistry that in 1890 the German Chemical Society organized an elaborate appreciation in Kekulé's honor, celebrating the twenty-fifth anniversary of his first benzene paper. Here Kekulé spoke of the creation of the theory. He said that he had discovered the ring shape of the benzene molecule after having a reverie or day-dream of a snake seizing its own tail (this is a common symbol in many ancient cultures known as the Ouroboros or Endless knot).[26] This vision, he said, came to him after years of studying the nature of carbon-carbon bonds. This was 7 years after he had solved the problem of how carbon atoms could bond to up to four other atoms at the same time. It is curious that a similar, humorous depiction of benzene had appeared in 1886 in the Berichte der Durstigen Chemischen Gesellschaft (Journal of the Thirsty Chemical Society), a parody of the Berichte der Deutschen Chemischen Gesellschaft, only the parody had monkeys seizing each other in a circle, rather than snakes as in Kekulé's anecdote.[27] Some historians have suggested that the parody was a lampoon of the snake anecdote, possibly already well known through oral transmission even if it had not yet appeared in print.[6] (Some others have speculated that Kekulé's story in 1890 was a re-parody of the monkey spoof, and was a mere invention rather than a recollection of an event in his life.[citation needed]) Kekulé's 1890 speech[28] in which these anecdotes appeared has been translated into English.[29] If the anecdote is the memory of a real event, circumstances mentioned in the story suggest that it must have happened early in 1862.[30] The cyclic nature of benzene was finally confirmed by the crystallographer Kathleen Lonsdale in 1929.[31][32] Early applications In the 19th and early-20th centuries, benzene was used as an after-shave lotion because of its pleasant smell. Prior to the 1920s, benzene was frequently used as an industrial solvent, especially for degreasing metal. As its toxicity became obvious, benzene was supplanted by other solvents, especially toluene (methyl benzene), which has similar physical properties but is not as carcinogenic. In 1903, Ludwig Roselius popularized the use of benzene to decaffeinate coffee. This discovery led to the production of Sanka. This process was later discontinued. Benzene was historically used as a significant component in many consumer products such as Liquid Wrench, several paint strippers, rubber cements, spot removers and other hydrocarbon-containing products. Some ceased manufacture of their benzene-containing formulations in about 1950, while others continued to use benzene as a component or significant contaminant until the late 1970s when leukemia deaths were found associated with Goodyear's Pliofilm production operations in Ohio. Until the late 1970s, many hardware stores, paint stores, and other retail outlets sold benzene in small cans, such as quart size, for general-purpose use.
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