The inhalation of benzene vapours causes irritation to the eyes and upper respiratory tract. What is the Kekulé structure? [66][67][68] The specific hematologic malignancies that benzene is associated with include: acute myeloid leukemia (AML), aplastic anemia, myelodysplastic syndrome (MDS), acute lymphoblastic leukemia (ALL), and chronic myeloid leukemia (CML).[69]. NQ01 mutations result in loss of function and may result in decreased detoxification. 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). In benzene, the atoms are hydrogens. The most important variations contain nitrogen. The EPA requires that spills or accidental releases into the environment of 10 pounds (4.5 kg) or more of benzene be reported. Here we discuss different aspects of the structure of benzene. [47] Benzene molecules have been detected on Mars.[48][49][50]. Via hydrogenation, benzene and its derivatives convert to cyclohexane and derivatives. As the carbon atoms in the benzene ring collided with each other, each carbon atom would collide twice with one neighbor during a given interval and then twice with its other neighbor during the next interval. Whereas alkenes can be hydrogenated near room temperatures, benzene and related compounds are more reluctant substrates, requiring temperatures >100 °C. Under these conditions, toluene undergoes dealkylation to benzene and methane: This irreversible reaction is accompanied by an equilibrium side reaction that produces [91] Benzene causes chromosomal aberrations in the peripheral blood leukocytes and bone marrow explaining the higher incidence of leukemia and multiple myeloma caused by chronic exposure. Kekule, a German scientist proposed the structure of benzene for the first time. The measurement of benzene in humans can be accomplished via urine, blood, and breath tests; however, all of these have their limitations because benzene is rapidly metabolized in the human body. Sulfonated benzene derivatives are useful detergents. Unfortunately, conventional atom-centered force fields provide only an approximate representation of these molecules owing to their failure to consider the quadrupole moment arising from the π electrons. It took several years to assign a structural formula to benzene because of its unusual stability and peculiar properties. GSH is involved with the formation of phenylmercapturic acid. [76], OSHA regulates levels of benzene in the workplace. The current ACGIH biological exposure limits for occupational exposure are 500 μg/g creatinine for muconic acid and 25 μg/g creatinine for phenylmercapturic acid in an end-of-shift urine specimen.[85][86][87][88]. The catechol is then metabolized to acetyl CoA and succinyl CoA, used by organisms mainly in the Citric Acid Cycle for energy production. In 2013, the biggest consumer country of benzene was China, followed by the USA. Benzene is built from hydrogen atoms (1s 1) and carbon atoms (1s 2 2s 2 2p x1 2p y1). The purpose of establishing an IDLH value is (1) to ensure that the worker can escape from a given contaminated environment in the event of failure of the respiratory protection equipment and (2) is considered a maximum level above which only a highly reliable breathing apparatus providing maximum worker protection is permitted [NIOSH 2004[82]]. Substantial quantities of epidemiologic, clinical, and laboratory data link benzene to aplastic anemia, acute leukemia, bone marrow abnormalities and cardiovascular disease. Because of the aromaticity, it is different from aliphatic compounds. 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 REL (10-hour) of 0.1 ppm. Chlorination is achieved with chlorine to give chlorobenzene in the presence of a Lewis acid catalyst such as aluminium tri-chloride. These p orbitals overlap, delocalizing the six electrons and making benzene a fully conjugated system. (1867) "Theoretische Betrachtungen und deren Anwendungen zur Systematik der organischen Chemie" (Theoretical considerations and their applications to the classification scheme of organic chemistry). Benzene itself can be measured in breath, blood or urine, but such testing is usually limited to the first 24 hours post-exposure due to the relatively rapid removal of the chemical by exhalation or biotransformation. In 1931, the American chemist Linus Pauling proposed that benzene had a unique structure, which was a resonance hybrid of both Kekulé structures. Studies have shown that genotype at these loci may influence susceptibility to the toxic effects of benzene exposure. von Hofmann isolated this benzene from coal tar. [77] The maximum allowable amount of benzene in workroom air during an 8-hour workday, 40-hour workweek is 1 ppm. [100][101], This article is about the chemical compound. 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]. [38] If the anecdote is the memory of a real event, circumstances mentioned in the story suggest that it must have happened early in 1862. ChEBI CHEBI:16716 A six-carbon aromatic annulene in which each carbon atom donates one of its two 2p electrons into a delocalised pi system. According to this theory, all the C-atoms in benzene are sp 2 -hybridized. Benzene is a cyclic hydrocarbon (chemical formula: C6H6), i.e., each carbon atom in benzene is arranged in a six-membered ring and is bonded to only one hydrogen atom. Benzene shows resonance as it has more than one way to place double bonds in the ring. Benzene is a colourless liquid with a characteristic odour and is primarily used in the production of polystyrene. (VIII. Long term inhalation of high levels of benzene results in headaches, dizziness, nausea, convulsions, coma and eventually death. Resonance form of a compound is nothing but another way of representing Lewis dot structure of that compound. It is sometimes abbreviated PhH. The current NIOSH definition for an IDLH condition, as given in the NIOSH Respirator Selection Logic, is one that poses a threat of exposure to airborne contaminants when that exposure is likely to cause death or immediate or delayed permanent adverse health effects or prevent escape from such an environment [NIOSH 2004]. The short term exposure limit for airborne benzene is 5 ppm for 15 minutes. The chemical formula for benzene is. Benzene has 6 hydrogen atoms, fewer than the corresponding parent alkane, hexane, which has 14. Curiously, a similar, humorous depiction of benzene had appeared in 1886 in a pamphlet entitled 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. Kekulé was the first to suggest a sensible structure for benzene. Benzene has been shown to cause cancer in both sexes of multiple species of laboratory animals exposed via various routes. It is a byproduct of the incomplete combustion of many materials. In 1866, August Kekulé used the principles of structural theory to postulate a structure for the benzene molecule. Molecular weight: 78 g mole-1 Myeloperoxidase mutations result in loss of function and may result in decreased generation of toxic metabolites. This reaction is achieved by the use of high pressures of hydrogen in the presence of heterogeneous catalysts, such as finely divided nickel. It was proposed to possess a cyclic arrangement of carbon atoms.Each carbon atom is attached to hydrogen atoms. Benzene, also known as benzol, is an organic chemical compound with the formula C 6 H 6.It is a colorless and flammable liquid with a sweet smell. [84] The NIOSH short-term exposure limit (STEL – 15 min) is 1 ppm. The formulas and structure reveal benzene as a pure. A small-area case-crossover study", "Advances in understanding benzene health effects and susceptibility", American Petroleum Institute, API Toxicological Review, Benzene, September 1948, "Advances in Understanding Benzene Health Effects and Susceptibility", International Agency for Research on Cancer, IARC Monographs on the Evaluation of Carcinogenic Risks to Humans, Overall Evaluations of Carcinogenicity: An Updating of IARC Monographs, "Benzene-induced cancers: abridged history and occupational health impact", "The toxicity of benzene and its metabolism and molecular pathology in human risk assessment", Occupational Safety and Health Standards, Toxic and Hazardous Substances, 1910.1028, Public Health Statement for Benzene, Agency for Toxic Substances and Disease Registry. , i.e it has 6 hydrogen- H atoms and six-carbon atoms and has an average mass of about 78.112. [79] This regulation is based on preventing benzene leukemogenesis. The interactions of aromatic groups have been identified as playing a crucial role in many systems of interest. Structure of benzene is a controversial topic because benzene has outstanding characteristics. of Health and Human Services: TR-289: Toxicology and Carcinogenesis Studies of Benzene, NLM Hazardous Substances Databank – Benzene, https://en.wikipedia.org/w/index.php?title=Benzene&oldid=998213989, GABAA receptor positive allosteric modulators, Wikipedia pages move-protected due to vandalism, Short description is different from Wikidata, Pages using collapsible list with both background and text-align in titlestyle, Articles containing unverified chemical infoboxes, Creative Commons Attribution-ShareAlike License, potential occupational carcinogen, flammable. It found that four contained benzene levels above World Health Organization limits. Benzene is an excellent ligand in the organometallic chemistry of low-valent metals. Some 20% of the benzene production is used to manufacture cumene, which is needed to produce phenol and acetone for resins and adhesives. Toluene disproportionation (TDP) is the conversion of toluene to benzene and xylene. Therefore, its chemical formula is C 6 H 6 . Due to this property, it is also known as a hydrocarbon. When benzene was discovered, it was found to yield only a single monosubstituted product. Structure of Benzene: Kekule benzene: two forms are in rapid equilibrium 154 pm 134 pm • All bonds are ~139 pm (intermediate between C-C and C=C) • Electron density is distributed evenly between the six carbons • Structure is planar, hexagonal • C–C–C bond angles are 120° • … The real structure is an intermediate of these structures represented by a resonance hybrid. OSHA has also established an action level of 0.5 ppm to encourage even lower exposures in the workplace.[81]. Prior to the 1920s, benzene was frequently used as an industrial solvent, especially for degreasing metal. Benzene is classified as a carcinogen, which increases the risk of cancer and other illnesses, and is also a notorious cause of bone marrow failure. With the global phaseout of leaded gasoline, benzene has made a comeback as a gasoline additive in some nations. very informative article of benzyne. Benzene has 6 hydrogen atoms – fewer than the corresponding parent alkane, hexane. The chemical formula for benzene is C6H6, i.e it has 6 hydrogen- H atoms and six-carbon atoms and has an average mass of about 78.112. [80] These legal limits were based on studies demonstrating compelling evidence of health risk to workers exposed to benzene. Benzene is sufficiently nucleophilic that it undergoes substitution by acylium ions and alkyl carbocations to give substituted derivatives. Each carbon atom has to join to three other atoms (one hydrogen and two carbons) and doesn't have enough unpaired electrons to form the required number of bonds, so it needs to promote one of the 2s 2 pair into the empty 2p z orbital. The C–C bond lengths are greater than a double bond (135 pm) but shorter than a single bond (147 pm). It is a compound consisting of only hydrogen and carbon atoms. It contains eight hydrogen atoms less than the corresponding parent hydrocarbon, i.e., hexane (C 6 H 14 ). The word "benzene" derives from "gum benzoin" (benzoin resin), an aromatic resin known to European pharmacists and perfumers since the 16th century as a product of southeast Asia. Agency for Toxic Substances and Disease Registry. Benzene: Patient information sheet, Drinking Water Contaminants|Organic Chemicals|Benzene, Benzene Toxicity: Standards and Regulations|ATSDR – Environmental Medicine & Environmental Health Education – CSEM, Documentation for Immediately Dangerous to Life or Health Concentrations (IDLH): Introduction, "Blood concentrations of volatile organic compounds in a nonoccupationally exposed US population and in groups with suspected exposure", "100 tonnes of pollutants spilled into Chinese river", "A Former Nazi Labor Camp in Austria, Now Billed as a Tourist Site", Dept. (This estimate assumes no threshold for benzene's carcinogenic effects.) [90], The paradigm of toxicological assessment of benzene is shifting towards the domain of molecular toxicology as it allows understanding of fundamental biological mechanisms in a better way. Hydrogen lies on the outer side of the ring structure. According to molecular orbital theory, benzene ring involves the formation of three delocalized π – orbitals spanning all six carbon atoms, while the valence bond theory describes two stable resonance structures for the ring. 125–129. Birch reduction, a non catalytic process, however selectively hydrogenates benzene to the diene. Benzene is a colorless and highly flammable liquid with a sweet smell, and is partially responsible for the aroma around petrol (gasoline) stations. The affected batches were removed from sale. [94] About 50% of the entire nationwide (United States) exposure to benzene results from smoking tobacco or from exposure to tobacco smoke. 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 products. Benzene structure. Benzene has been recognized as a toxic substance that causes acute and chronic health problems. These genes may be targets for genetic screening for susceptibility to benzene toxicity. This process was later discontinued. "Kekule Structure of Benzene" in 1865, after years of discovery of benzene, Kekule suggested that: The benzene molecule is made up of a hexagon of six carbon atoms. "VIII. As a consequence, gasoline often contained several percent benzene before the 1950s, when tetraethyl lead replaced it as the most widely used antiknock additive. Using electrophilic aromatic substitution, many functional groups are introduced onto the benzene framework. Individuals carrying variant of NAD(P)H:quinone oxidoreductase 1 (NQO1), microsomal epoxide hydrolase (EPHX) and deletion of the glutathione S-transferase T1 (GSTT1) showed a greater frequency of DNA single-stranded breaks.[93]. Benzene has a cyclic structure with C-C double bonds. Benzoic acid and its salts undergo decarboxylation to benzene. 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). Long-term exposure to excessive levels of benzene in the air causes leukemia, a potentially fatal cancer of the blood-forming organs. For example, mutations in CYP2E1 increase activity and result in increased generation of toxic metabolites. The American Petroleum Institute (API) stated in 1948 that "it is generally considered that the only absolutely safe concentration for benzene is zero". Many important chemical compounds are derived from benzene by replacing one or more of its hydrogen atoms with another functional group. Die aromatischen Verbindungen. In 2005, the water supply to the city of Harbin in China with a population of almost nine million people, was cut off because of a major benzene exposure. In 1845, Charles Mansfield, working under August Wilhelm von Hofmann, isolated benzene from coal tar. The molecule is planar. It behaves both as saturated and unsaturated hydrocarbon. The double bonds within this structure are mainly separated by a single bond, hence this arrangement is recognized to have conjugated double bonds. The hydrocarbon derived from benzoic acid thus acquired the name benzin, benzol, or benzene. In heterocycles, carbon atoms in the benzene ring are replaced with other elements. Phenol and halobenzenes can be reduced with metals. Benzene. [32][33] 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 disubstituted derivative—now understood to correspond to the ortho, meta, and para patterns of arene substitution—to argue in support of his proposed structure. 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. In nitration, benzene reacts with nitronium ions (NO2+), which is a strong electrophile produced by combining sulfuric and nitric acids. For other uses, see, Except where otherwise noted, data are given for materials in their, Biological oxidation and carcinogenic activity, Critics pointed out a problem with Kekulé's original (1865) structure for benzene: Whenever benzene underwent substitution at the ortho position, two distinguishable isomers should have resulted, depending on whether a double bond or a single bond existed between the carbon atoms to which the substituents were attached; however, no such isomers were observed. Das Benzol." As its toxicity became obvious, benzene was supplanted by other solvents, especially toluene (methylbenzene), which has similar physical properties but is not as carcinogenic. 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. The most common reactions of benzene involve substitution of a proton by other groups. In some systems, even the benzene-to-xylenes ratio is modified to favor xylenes. [52] The molecular orbital description involves the formation of three delocalized π orbitals spanning all six carbon atoms, while the valence bond description involves a superposition of resonance structures. In particular, acute myeloid leukemia or acute nonlymphocytic leukemia (AML & ANLL) is not disputed to be caused by benzene. A circle is used as an alternative symbol inside the hexagon that is used to represent six pi electrons. Its structure and some of the properties are as follows. Although of no commercial significance, many other routes to benzene exist. Further loss of hydrogen gives "fused" aromatic hydrocarbons, such as naphthalene, anthracene, phenanthrene, and pyrene. Thanks to the Kekule st… As it contains only carbon and hydrogen atoms, benzene is classed as a hydrocarbon. More than half of the entire benzene production is processed into ethylbenzene, a precursor to styrene, which is used to make polymers and plastics like polystyrene and EPS. [12], Benzene is a natural constituent of crude oil and is one of the elementary petrochemicals. [69][89], Genetic polymorphisms in these enzymes may induce loss of function or gain of function. [71] The US Department of Health and Human Services (DHHS) classifies benzene as a human carcinogen. According to the ATSDR Toxicological Profile for benzene, between 1978 and 1981, catalytic reformates accounted for approximately 44–50% of the total U.S benzene production.[47]. These aberrations can be monitored using fluorescent in situ hybridization (FISH) with DNA probes to assess the effects of benzene along with the hematological tests as markers of hematotoxicity. Several enzymes are involved. Resonance forms or resonating structures only differ in arrangement of electrons. The limit of the fusion process is the hydrogen-free allotrope of carbon, graphite. It is a colorless liquid with a characteristic odor. The solvent-properties of the two are similar, but toluene is less toxic and has a wider liquid range. The single and double bonds alternate each other. Thus, a double bond would exist with one neighbor during the first interval and with the other neighbor during the next interval. Benzene | C6H6 | CID 241 - structure, chemical names, physical and chemical properties, classification, patents, literature, biological activities, safety/hazards/toxicity information, supplier lists, and more. [92] Benzene metabolism involves enzymes coded for by polymorphic genes. The compound appears like a colourless liquid having a characteristic odour. Due to the chemical formula, benzene is categorized as a hydrocarbon. Pure benzene, for example, oxidizes in the body to produce an epoxide, benzene oxide, which is not excreted readily and can interact with DNA to produce harmful mutations. [83] In September 1995, NIOSH issued a new policy for developing recommended exposure limits (RELs) for substances, including carcinogens. Benzene is widely utilized chemicals that are involved in various manufacturing products that we use daily such as plastics, detergents, and rubber.