structure of benzene

Kekule, a German scientist proposed the structure of benzene for the first time. The major sources of benzene exposure are tobacco smoke, automobile service stations, exhaust from motor vehicles, and industrial emissions; however, ingestion and dermal absorption of benzene can also occur through contact with contaminated water. Benzene is used mainly as an intermediate to make other chemicals, above all ethylbenzene, cumene, cyclohexane, nitrobenzene, and alkylbenzene. Benzene is built from hydrogen atoms (1s 1) and carbon atoms (1s 2 2s 2 2p x1 2p y1). X-ray diffraction shows that all six carbon-carbon bonds in benzene are of the same length, at 140 picometres (pm). Structure of the benzene molecule. [70] There is no safe exposure level; even tiny amounts can cause harm. Most of these metabolites have some value as biomarkers of human exposure, since they accumulate in the urine in proportion to the extent and duration of exposure, and they may still be present for some days after exposure has ceased. In this hydrogen-intensive process, toluene is mixed with hydrogen, then passed over a chromium, molybdenum, or platinum oxide catalyst at 500–650 °C and 20–60 atm pressure. In the body, benzene is enzymatically converted to a series of oxidation products including muconic acid, phenylmercapturic acid, phenol, catechol, hydroquinone and 1,2,4-trihydroxybenzene. One way of understanding the carcinogenic effects of benzene is by examining the products of biological oxidation. In his 1890 paper, Armstrong represented benzene nuclei within polycyclic benzenoids by placing inside the benzene nuclei a letter "C", an abbreviation of the word "centric". (2007). From p. 102: " … benzene, according to this view, may be represented by a double ring, in fact." [76], OSHA regulates levels of benzene in the workplace. Sometimes, xylenes and heavier aromatics are used in place of toluene, with similar efficiency. The single and double bonds alternate each other. Scientific evidence has established that employee exposure to low levels of benzene can cause leukemia and other diseases of the blood-forming organs, such as multiple myeloma, a cancer of the plasma cells as well as anemia and low blood count which can result in tiredness, lung infections and bruising of the skin. Benzene, C 6 H 6, is a planar molecule containing a ring of six carbon atoms, each with a hydrogen atom attached. The six carbon atoms form a perfectly regular hexagon. Due to the cyclic continuous pi bonds between the carbon atoms, benzene is classed as an aromatic hydrocarbon. Hydrogen lies on the outer side of the ring structure. Following were taken into consideration to determine the structure of Benzene. The most important variations contain nitrogen. [16][17] In 1833, Eilhard Mitscherlich produced it by distilling benzoic acid (from gum benzoin) and lime. It is a compound consisting of only hydrogen and carbon atoms. Structure of the Benzene Molecule. Via hydrogenation, benzene and its derivatives convert to cyclohexane and derivatives. Its … 11,960) for the fractional distillation of coal tar. The United States Environmental Protection Agency has set a maximum contaminant level (MCL) for benzene in drinking water at 0.005 mg/L (5 ppb), as promulgated via the U.S. National Primary Drinking Water Regulations. Long-term exposure to excessive levels of benzene in the air causes leukemia, a potentially fatal cancer of the blood-forming organs. Smaller amounts of benzene are used to make some types of rubbers, lubricants, dyes, detergents, drugs, explosives, and pesticides. The formulas and structure reveal benzene as a pure aromatic hydrocarbon, wherein it is also defined as a compound composing hydrogen & carbon having alternate double bonds in the form of the ring. Benzene has 2 resonance structures but taken individually none show the delocalisation of electrons and they can exist at the same time as electrons are delocalised. Further loss of hydrogen gives "fused" aromatic hydrocarbons, such as naphthalene, anthracene, phenanthrene, and pyrene. Benzene production is currently expanding in the Middle East and in Africa, whereas production capacities in Western Europe and North America are stagnating. Replacement of a second CH bond with N gives, depending on the location of the second N, pyridazine, pyrimidine, or pyrazine. The inhalation of benzene vapours causes irritation to the eyes and upper respiratory tract. In the bone marrow, MPO converts these polyphenols to benzoquinones. It is used primarily as a precursor to the manufacture of chemicals with more complex structure, such as ethylbenzene and cumene, of which billions of kilograms are produced annually. The United States Environmental Protection Agency introduced new regulations in 2011 that lowered the benzene content in gasoline to 0.62%. [95] After smoking 32 cigarettes per day, the smoker would take in about 1.8 milligrams (mg) of benzene. To provide a mechanism for the conversion process, Kekulé proposed that the valency of an atom is determined by the frequency with which it collided with its neighbors in a molecule. Pyrolysis gasoline can be blended with other hydrocarbons as a gasoline additive, or routed through an extraction process to recover BTX aromatics (benzene, toluene and xylenes). NQ01 metabolizes benzoquinone toward polyphenols (counteracting the effect of MPO). According to Kekule, all the 6 carbon atoms of benzene molecule are joint to each other by alternate single and double bond forming a hexagonal ring and a hydrogen atom is bonded to each carbon atom. (1867) "Theoretische Betrachtungen und deren Anwendungen zur Systematik der organischen Chemie" (Theoretical considerations and their applications to the classification scheme of organic chemistry). Required fields are marked *, Benzene is one of the most commonly known aromatic compounds with chemical formula, The structural representation of benzene is as shown in the figure below. In similar fashion to this catalytic reforming, UOP and BP commercialized a method from LPG (mainly propane and butane) to aromatics. Today, most benzene comes from the petrochemical industry, with only a small fraction being produced from coal. The structure has a six-carbon ring which is represented by a hexagon and it includes 3-double bonds. Toluene disproportionation (TDP) is the conversion of toluene to benzene and xylene. Charles Mansfield filed for (November 11, 1847) and received (May 1848) a patent (no. [97], Under specific conditions and in the presence of other chemicals benzoic acid (a preservative) and ascorbic acid (Vitamin C) may interact to produce benzene. It is a compound consisting of only hydrogen and carbon atoms. As it contains only carbon and hydrogen atoms, benzene is classed as a hydrocarbon. The carbon atoms are represented by a corner that is bonded to other atoms. Benzene has been shown to cause cancer in both sexes of multiple species of laboratory animals exposed via various routes. [47] Benzene molecules have been detected on Mars.[48][49][50]. The limit of the fusion process is the hydrogen-free allotrope of carbon, graphite. [63] In many European languages, the word for petroleum or gasoline is an exact cognate of "benzene". In 1855, Hofmann used the word "aromatic" to designate this family relationship, after a characteristic property of many of its members. [80] These legal limits were based on studies demonstrating compelling evidence of health risk to workers exposed to benzene. See: Kolmetz, Gentry, Guidelines for BTX Revamps, AIChE 2007 Spring Conference. All the carbons have … Nitrobenzene is the precursor to aniline. United States Environmental Protection Agency, US Department of Health and Human Services, Agency for Toxic Substances and Disease Registry, Occupational Safety and Health Administration, National Institute for Occupational Safety and Health, an explosion at a China National Petroleum Corporation (CNPC) factory, Industrial Union Department v. American Petroleum Institute, "Surface tension measurements show that chaotropic salting-in denaturants are not just water-structure breakers", "Benzene - an overview | ScienceDirect Topics", Ullmann's Encyclopedia of Industrial Chemistry, "On new compounds of carbon and hydrogen, and on certain other products obtained during the decomposition of oil by heat", Philosophical Transactions of the Royal Society, "Über das Benzol und die Säuren der Oel- und Talgarten", "On the oxidation of phenyl alcohol, and a mechanical arrangement adapted to illustrate structure in the non-saturated hydrocarbons", "An explanation of the laws which govern substitution in the case of benzenoid compounds". 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). Benzene | C6H6 | CID 241 - structure, chemical names, physical and chemical properties, classification, patents, literature, biological activities, safety/hazards/toxicity information, supplier lists, and more. Benzene structure was found by Kekule in 1872. [69][89], Genetic polymorphisms in these enzymes may induce loss of function or gain of function. These intermediates and metabolites induce genotoxicity by multiple mechanisms including inhibition of topoisomerase II (which maintains chromosome structure), disruption of microtubules (which maintains cellular structure and organization), generation of oxygen free radicals (unstable species) that may lead to point mutations, increasing oxidative stress, inducing DNA strand breaks, and altering DNA methylation (which can affect gene expression). [46], Trace amounts of benzene are found in petroleum and coal. Examples of simple benzene derivatives are phenol, toluene, and aniline, abbreviated PhOH, PhMe, and PhNH2, respectively. Molecular weight: 78 g mole-1 Benzene is widely utilized chemicals that are involved in various manufacturing products that we use daily such as plastics, detergents, and rubber. The interactions of aromatic groups have been identified as playing a crucial role in many systems of interest. Benzene and cyclohexane have a similar structure, only the ring (of delocalized electrons) inside Benzene distinguishes it from cyclohexane. According to the experiments, the single (CC) and double (C = C) covalent bonds have a bond length of 0.154 nm and 0.134 nm, respectively. To accurately reflect the nature of the bonding, benzene is often depicted with a circle inside a hexagonal arrangement of carbon atoms. As benzene can cause cancer, NIOSH recommends that all workers wear special breathing equipment when they are likely to be exposed to benzene at levels exceeding the recommended (8-hour) exposure limit of 0.1 ppm.[78]. The Structure and Geometry of Benzene All the carbon atoms in benzene are sp 2 hybridized connected by sp2 – sp2 single bonds and each has a p orbital perpendicular to the plane of the atoms. It was August Kekule who put forth the structure of benzene. Using electrophilic aromatic substitution, many functional groups are introduced onto the benzene framework. The carbon atoms are represented by a corner that is bonded to other atoms. So, the presence of a benzene ring in the structure of a compound isn’t an automatic cause for concern – in fact, a large number of compounds found in our food contain a benzene ring somewhere in their structure! The Kekulé structure for benzene, C 6 H 6. In this process, the xylene stream exiting the TDP unit is approximately 90% p-xylene. Due to the chemical formula, benzene is categorized as a hydrocarbon. 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. Benzene targets the liver, kidney, lung, heart and brain and can cause DNA strand breaks, chromosomal damage, etc. Hydroquinone, benzenetriol and catechol are converted to polyphenols. This intermediate distance is consistent with electron delocalization: the electrons for C–C bonding are distributed equally between each of the six carbon atoms. GSH mutations or deletions result in loss of function and result in decreased detoxification. The most common reactions of benzene involve substitution of a proton by other groups. (This estimate assumes no threshold for benzene's carcinogenic effects.) The hydrocarbon derived from benzoic acid thus acquired the name benzin, benzol, or benzene. The molecular formula of benzene is C 6 H 6. Trimerization of acetylene gives benzene. Benzene is one of the most commonly known aromatic compounds with chemical formula C6H6. (VIII. This means that every carbon atom is capable of chemical bonds with four other atoms. 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