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Benzene
Benzene
is an important organic chemical compound with the chemical formula C6H6. The benzene molecule is composed of six carbon atoms joined in a ring with one hydrogen atom attached to each. As it contains only carbon and hydrogen atoms, benzene is classed as a hydrocarbon. Benzene
Benzene
is a natural constituent of crude oil and is one of the elementary petrochemicals. Due to the cyclic continuous pi bond between the carbon atoms, benzene is classed as an aromatic hydrocarbon, the second [n]-annulene ([6]-annulene). It is sometimes abbreviated Ph–H. Benzene
Benzene
is a colorless and highly flammable liquid with a sweet smell, and is responsible for the aroma around petrol stations. 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. As benzene has a high octane number, it is an important component of gasoline. As benzene is a human carcinogen, most non-industrial applications have been limited.

Contents

1 History

1.1 Discovery 1.2 Ring formula 1.3 Nomenclature 1.4 Early applications 1.5 Occurrence

2 Structure 3 Benzene
Benzene
derivatives 4 Production

4.1 Catalytic reforming 4.2 Toluene
Toluene
hydrodealkylation 4.3 Toluene
Toluene
disproportionation 4.4 Steam cracking 4.5 Other methods

5 Uses

5.1 Component of gasoline

6 Reactions

6.1 Sulfonation, chlorination, nitration 6.2 Hydrogenation 6.3 Metal complexes

7 Health effects 8 Exposure to benzene

8.1 Benzene
Benzene
exposure limits 8.2 Toxicology

8.2.1 Biomarkers of exposure 8.2.2 Biotransformations 8.2.3 Molecular toxicology 8.2.4 Biological oxidation and carcinogenic activity

8.3 Routes of exposure

8.3.1 Inhalation 8.3.2 Exposure from soft drinks 8.3.3 Contamination of water supply

9 See also 10 References 11 External links

History[edit] Discovery[edit] The word "benzene" derives from "gum benzoin" (benzoin resin), an aromatic resin known to European pharmacists and perfumers since the 15th century as a product of southeast Asia.[11] An acidic material was derived from benzoin by sublimation, and named "flowers of benzoin", or benzoic acid. The hydrocarbon derived from benzoic acid thus acquired the name benzin, benzol, or benzene.[12] Michael Faraday first isolated and identified benzene in 1825 from the oily residue derived from the production of illuminating gas, giving it the name bicarburet of hydrogen.[13][14] In 1833, Eilhard Mitscherlich
Eilhard Mitscherlich
produced it by distilling benzoic acid (from gum benzoin) and lime. He gave the compound the name benzin.[15] In 1836, the French chemist Auguste Laurent named the substance "phène";[16] this word has become the root of the English word "phenol", which is hydroxylated benzene, and "phenyl", the radical formed by abstraction of a hydrogen atom (free radical H•) from benzene.

Kekulé's 1872 modification of his 1865 theory, illustrating rapid alternation of double bonds[17]

. In 1845, Charles Mansfield, working under August Wilhelm von Hofmann, isolated benzene from coal tar.[18] Four years later, Mansfield began the first industrial-scale production of benzene, based on the coal-tar method.[19][20] Gradually, the sense developed among chemists that a number of substances were chemically related to benzene, comprising a diverse chemical family. In 1855, Hofmann used the word "aromatic" to designate this family relationship, after a characteristic property of many of its members.[21] In 1997, benzene was detected in deep space.[22] Ring formula[edit]

Historic benzene structures (from left to right) by Claus (1867),[23] Dewar (1867),[24] Ladenburg (1869),[25] Armstrong (1887),[26] Thiele (1899)[27][28] and Kekulé (1865). Dewar benzene
Dewar benzene
and prismane are different chemicals that have Dewar's and Ladenburg's structures. Thiele and Kekulé's structures are used today.

The empirical formula for benzene was long known, but its highly polyunsaturated structure, with just one hydrogen atom for each carbon atom, was challenging to determine. Archibald Scott Couper
Archibald Scott Couper
in 1858 and Joseph Loschmidt
Joseph Loschmidt
in 1861[29] suggested possible structures that contained multiple double bonds or multiple rings, but too little evidence was then available to help chemists decide on any particular structure. In 1865, the German chemist Friedrich August Kekulé
August Kekulé
published a paper in French (for he was then teaching in Francophone Belgium) suggesting that the structure contained a ring of six carbon atoms with alternating single and double bonds. The next year he published a much longer paper in German on the same subject.[30][31] 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.[32] Kekulé's symmetrical ring could explain these curious facts, as well as benzene's 1:1 carbon-hydrogen ratio. The new 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
Ouroboros
or Endless knot).[33] 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. 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.[34] 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.[12] Kekulé's 1890 speech[35] in which this anecdote appeared has been translated into English.[36] If the anecdote is the memory of a real event, circumstances mentioned in the story suggest that it must have happened early in 1862.[37] The cyclic nature of benzene was finally confirmed by the crystallographer Kathleen Lonsdale
Kathleen Lonsdale
in 1929.[38][39] Nomenclature[edit] The German chemist Wilhelm Körner
Wilhelm Körner
suggested the prefixes ortho-, meta-, para- to distinguish di-substituted benzene derivatives in 1867; however, he did not use the prefixes to distinguish the relative positions of the substituents on a benzene ring.[40] It was the German chemist Karl Gräbe who, in 1869, first used the prefixes ortho-, meta-, para- to denote specific relative locations of the substituents on a di-substituted aromatic ring (viz, naphthalene).[41] In 1870, the German chemist Viktor Meyer
Viktor Meyer
first applied Gräbe's nomenclature to benzene.[42] Early applications[edit] 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 (methylbenzene), which has similar physical properties but is not as carcinogenic. In 1903, Ludwig Roselius
Ludwig Roselius
popularized the use of benzene to decaffeinate coffee. This discovery led to the production of Sanka. This process was later discontinued. Benzene
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. Manufacture of some of these benzene-containing formulations ceased in about 1950, although Liquid Wrench continued to contain significant amounts of benzene until the late 1970s.[citation needed] Occurrence[edit] Trace amounts of benzene are found in petroleum and coal. It is a byproduct of the incomplete combustion of many materials. For commercial use, until World War II, most benzene was obtained as a by-product of coke production (or "coke-oven light oil") for the steel industry. However, in the 1950s, increased demand for benzene, especially from the growing polymers industry, necessitated the production of benzene from petroleum. Today, most benzene comes from the petrochemical industry, with only a small fraction being produced from coal.[43] Structure[edit] Main article: Aromaticity

The various representations of benzene

X-ray diffraction
X-ray diffraction
shows that all six carbon-carbon bonds in benzene are of the same length, at 140 picometres (pm)[citation needed]. The C–C bond lengths are greater than a double bond (135 pm) but shorter than a single bond (147 pm). This intermediate distance is consistent with electron delocalization: the electrons for C–C bonding are distributed equally between each of the six carbon atoms. Benzene
Benzene
has 6 hydrogen atoms – fewer than the corresponding parent alkane, hexane. The molecule is planar.[44] The MO description involves the formation of three delocalized π orbitals spanning all six carbon atoms, while the VB description involves a superposition of resonance structures.[45][46][47][48] It is likely that this stability contributes to the peculiar molecular and chemical properties known as aromaticity. To accurately reflect the nature of the bonding, benzene is often depicted with a circle inside a hexagonal arrangement of carbon atoms. Derivatives of benzene occur sufficiently often as a component of organic molecules that the Unicode
Unicode
Consortium has allocated a symbol in the Miscellaneous Technical block with the code U+232C (⌬) to represent it with three double bonds,[49] and U+23E3 (⏣) for a delocalized version.[50] Benzene
Benzene
derivatives[edit] Main articles: Aromatic
Aromatic
hydrocarbons and Alkylbenzenes Many important chemical compounds are derived from benzene by replacing one or more of its hydrogen atoms with another functional group. Examples of simple benzene derivatives are phenol, toluene, and aniline, abbreviated PhOH, PhMe, and PhNH2, respectively. Linking benzene rings gives biphenyl, C6H5–C6H5. Further loss of hydrogen gives "fused" aromatic hydrocarbons, such as naphthalene and anthracene. The limit of the fusion process is the hydrogen-free allotrope of carbon, graphite. In heterocycles, carbon atoms in the benzene ring are replaced with other elements. The most important variations contain nitrogen. Replacing one CH with N gives the compound pyridine, C5H5N. Although benzene and pyridine are structurally related, benzene cannot be converted into pyridine. Replacement of a second CH bond with N gives, depending on the location of the second N, pyridazine, pyrimidine, and pyrazine.[51] Production[edit] Four chemical processes contribute to industrial benzene production: catalytic reforming, toluene hydrodealkylation, toluene disproportionation, and steam cracking. According to the ATSDR Toxicological Profile for benzene, between 1978 and 1981, catalytic reformats accounted for approximately 44–50% of the total U.S benzene production.[43] Catalytic reforming[edit] In catalytic reforming, a mixture of hydrocarbons with boiling points between 60–200 °C is blended with hydrogen gas and then exposed to a bifunctional platinum chloride or rhenium chloride catalyst at 500–525 °C and pressures ranging from 8–50 atm. Under these conditions, aliphatic hydrocarbons form rings and lose hydrogen to become aromatic hydrocarbons. The aromatic products of the reaction are then separated from the reaction mixture (or reformate) by extraction with any one of a number of solvents, including diethylene glycol or sulfolane, and benzene is then separated from the other aromatics by distillation. The extraction step of aromatics from the reformate is designed to produce aromatics with lowest non-aromatic components. Recovery of the aromatics, commonly referred to as BTX (benzene, toluene and xylene isomers), involves such extraction and distillation steps. There are a good many licensed processes available for extraction of the aromatics. In similar fashion to this catalytic reforming, UOP and BP commercialized a method from LPG (mainly propane and butane) to aromatics. Toluene
Toluene
hydrodealkylation[edit] Toluene
Toluene
hydrodealkylation converts toluene to benzene. In this hydrogen-intensive process, toluene is mixed with hydrogen, then passed over a chromium, molybdenum, or platinum oxide catalyst at 500–600 °C and 40–60 atm pressure. Sometimes, higher temperatures are used instead of a catalyst (at the similar reaction condition). Under these conditions, toluene undergoes dealkylation to benzene and methane:

C6H5CH3 + H2 → C6H6 + CH4

This irreversible reaction is accompanied by an equilibrium side reaction that produces biphenyl (aka diphenyl) at higher temperature:

2 C 6H 6 ⇌ H 2 + C 6H 5–C 6H 5

If the raw material stream contains much non-aromatic components (paraffins or naphthenes), those are likely decomposed to lower hydrocarbons such as methane, which increases the consumption of hydrogen. A typical reaction yield exceeds 95%. Sometimes, xylenes and heavier aromatics are used in place of toluene, with similar efficiency. This is often called "on-purpose" methodology to produce benzene, compared to conventional BTX (benzene-toluene-xylene) extraction processes. Toluene
Toluene
disproportionation[edit] Where a chemical complex has similar demands for both benzene and xylene, then toluene disproportionation (TDP) may be an attractive alternative to the toluene hydrodealkylation. In the broad sense, 2 toluene molecules are reacted and the methyl groups rearranged from one toluene molecule to the other, yielding one benzene molecule and one xylene molecule. Given that demand for para-xylene (p-xylene) substantially exceeds demand for other xylene isomers, a refinement of the TDP process called Selective TDP (STDP) may be used. In this process, the xylene stream exiting the TDP unit is approximately 90% paraxylene. In some current catalytic systems, even the benzene-to-xylenes ratio is decreased (more xylenes) when the demand of xylenes is higher. Steam cracking[edit] Steam cracking
Steam cracking
is the process for producing ethylene and other alkenes from aliphatic hydrocarbons. Depending on the feedstock used to produce the olefins, steam cracking can produce a benzene-rich liquid by-product called pyrolysis gasoline. 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). Other methods[edit] Although of no commercial significance, many other routes to benzene exist. Phenol
Phenol
and halobenzenes can be reduced with metals. Benzoic acid and its salts undergo decarboxylation to benzene. Via the reaction the diazonium compound with hypophosphorus acid aniline gives benzene. Trimerization
Trimerization
of acetylene gives benzene. Uses[edit] Benzene
Benzene
is used mainly as an intermediate to make other chemicals, above all ethylbenzene, cumene, cyclohexane, nitrobenzene, and alkylbenzene. 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. Some 20% of the benzene production is used to manufacture cumene, which is needed to produce phenol and acetone for resins and adhesives. Cyclohexane consumes ca. 10% of the world's benzene production; it is primarily used in the manufacture of nylon fibers, which are processed into textiles and engineering plastics. Smaller amounts of benzene are used to make some types of rubbers, lubricants, dyes, detergents, drugs, explosives, and pesticides. In 2013, the biggest consumer country of benzene was China, followed by the USA. Benzene
Benzene
production is currently expanding in the Middle East and in Africa, whereas production capacities in Western Europe and North America are stagnating.[52] Toluene
Toluene
is now often used as a substitute for benzene, for instance as a fuel additive. The solvent-properties of the two are similar, but toluene is less toxic and has a wider liquid range. Toluene
Toluene
is also processed into benzene.[53]

Major commodity chemicals and polymers derived from benzene. Clicking on the image loads the appropriate article

Component of gasoline[edit] As a gasoline (petrol) additive, benzene increases the octane rating and reduces knocking. As a consequence, gasoline often contained several percent benzene before the 1950s, when tetraethyl lead replaced it as the most widely used antiknock additive. With the global phaseout of leaded gasoline, benzene has made a comeback as a gasoline additive in some nations. In the United States, concern over its negative health effects and the possibility of benzene's entering the groundwater have led to stringent regulation of gasoline's benzene content, with limits typically around 1%.[54] European petrol specifications now contain the same 1% limit on benzene content. The United States
United States
Environmental Protection Agency introduced new regulations in 2011 that lowered the benzene content in gasoline to 0.62%.[55] Reactions[edit] The most common reactions of benzene involve substitution of a proton by other groups.[56] Electrophilic aromatic substitution
Electrophilic aromatic substitution
is a general method of derivatizing benzene. Benzene
Benzene
is sufficiently nucleophilic that it undergoes substitution by acylium ions and alkyl carbocations to give substituted derivatives.

Electrophilic aromatic substitution
Electrophilic aromatic substitution
of benzene

The most widely practiced example of this reaction is the ethylation of benzene.

Approximately 24,700,000 tons were produced in 1999.[57] Highly instructive but of far less industrial significance is the Friedel-Crafts alkylation
Friedel-Crafts alkylation
of benzene (and many other aromatic rings) using an alkyl halide in the presence of a strong Lewis acid
Lewis acid
catalyst. Similarly, the Friedel-Crafts acylation
Friedel-Crafts acylation
is a related example of electrophilic aromatic substitution. The reaction involves the acylation of benzene (or many other aromatic rings) with an acyl chloride using a strong Lewis acid
Lewis acid
catalyst such as aluminium chloride or Iron(III) chloride.

Friedel-Crafts acylation
Friedel-Crafts acylation
of benzene by acetyl chloride

Sulfonation, chlorination, nitration[edit] Using electrophilic aromatic substitution, many functional groups are introduced onto the benzene framework. Sulfonation of benzene involves the use of oleum, a mixture of sulfuric acid with sulfur trioxide. Sulfonated benzene derivatives are useful detergents. In nitration, benzene reacts with nitronium ions (NO2+), which is a strong electrophile produced by combining sulfuric and nitric acids. Nitrobenzene
Nitrobenzene
is the precursor to aniline. Chlorination is achieved with chlorine to give chlorobenzene in the presence of a catalyst such as aluminium tri-chloride. Hydrogenation[edit] Via hydrogenation, benzene and its derivatives convert to cyclohexane and derivatives. This reaction is achieved by the use of high pressures of hydrogen in the presence of heterogeneous catalysts, such as finely divided nickel. Whereas alkenes can be hydrogenated near room temperatures, benzene and related compounds are more reluctant substrates, requiring temperatures >100 °C. This reaction is practiced on a large scale industrially. In the absence of the catalyst, benzene is impervious to hydrogen. Hydrogenation
Hydrogenation
cannot be stopped to give cyclohexene or cyclohexadienes as these are superior substrates. Birch reduction, a non catalytic process, however selectively hydrogenates benzene to the diene. Metal complexes[edit] Benzene
Benzene
is an excellent ligand in the organometallic chemistry of low-valent metals. Important examples include the sandwich and half-sandwich complexes, respectively, Cr(C6H6)2 and [RuCl2(C6H6)]2. Health effects[edit]

A bottle of benzene. The warnings show benzene is a toxic and flammable liquid.

Benzene
Benzene
increases the risk of cancer and other illnesses, and is also a notorious cause of bone marrow failure. Substantial quantities of epidemiologic, clinical, and laboratory data link benzene to aplastic anemia, acute leukemia, bone marrow abnormalities and cardiovascular disease.[58][59][60] 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).[61] The American Petroleum
Petroleum
Institute (API) stated in 1948 that "it is generally considered that the only absolutely safe concentration for benzene is zero".[62] There is no safe exposure level; even tiny amounts can cause harm.[63] The US Department of Health and Human Services (DHHS) classifies benzene as a human carcinogen. Long-term exposure to excessive levels of benzene in the air causes leukemia, a potentially fatal cancer of the blood-forming organs. In particular, acute myeloid leukemia or acute nonlymphocytic leukemia (AML & ANLL) is not disputed to be caused by benzene.[64] IARC rated benzene as "known to be carcinogenic to humans" (Group 1). As benzene is ubiquitous in gasoline and hydrocarbon fuels are in use everywhere, human exposure to benzene is a global health problem. Benzene
Benzene
targets liver, kidney, lung, heart and the brain and can cause DNA
DNA
strand breaks, chromosomal damage, etc. Benzene
Benzene
causes cancer in animals including humans. Benzene
Benzene
has been shown to cause cancer in both sexes of multiple species of laboratory animals exposed via various routes.[65][66] Exposure to benzene[edit] According to the Agency for Toxic Substances and Disease Registry (ATSDR) (2007), benzene is both an anthropogenically produced and naturally occurring chemical from processes that include: volcanic eruptions, wild fires, synthesis of chemicals such as phenol, production of synthetic fibers, and fabrication of rubbers, lubricants, pesticides, medications, and dyes. 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
Benzene
is hepatically metabolized and excreted in the urine. Measurement of air and water levels of benzene is accomplished through collection via activated charcoal tubes, which are then analyzed with a gas chromatograph. 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.[67] OSHA regulates levels of benzene in the workplace.[68] The maximum allowable amount of benzene in workroom air during an 8-hour workday, 40-hour workweek is 1 ppm. 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.[69] Benzene
Benzene
exposure limits[edit] The United States
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
Water
Regulations.[70] This regulation is based on preventing benzene leukemogenesis. The maximum contaminant level goal (MCLG), a nonenforceable health goal that would allow an adequate margin of safety for the prevention of adverse effects, is zero benzene concentration in drinking water. The EPA requires that spills or accidental releases into the environment of 10 pounds (4.5 kg) or more of benzene be reported. The U.S. Occupational Safety and Health Administration
Occupational Safety and Health Administration
(OSHA) has set a permissible exposure limit of 1 part of benzene per million parts of air (1 ppm) in the workplace during an 8-hour workday, 40-hour workweek. The short term exposure limit for airborne benzene is 5 ppm for 15 minutes.[71] These legal limits were based on studies demonstrating compelling evidence of health risk to workers exposed to benzene. The risk from exposure to 1 ppm for a working lifetime has been estimated as 5 excess leukemia deaths per 1,000 employees exposed. (This estimate assumes no threshold for benzene's carcinogenic effects.) OSHA has also established an action level of 0.5 ppm to encourage even lower exposures in the workplace.[72] The U.S. National Institute for Occupational Safety and Health
National Institute for Occupational Safety and Health
(NIOSH) revised the Immediately Dangerous to Life and Health
Immediately Dangerous to Life and Health
(IDLH) concentration for benzene to 500 ppm. The current NIOSH definition for an IDLH
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 purpose of establishing an IDLH
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[73]].[74] In September 1995, NIOSH issued a new policy for developing recommended exposure limits (RELs) for substances, including carcinogens. 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.[75] The NIOSH short-term exposure limit (STEL – 15 min) is 1 ppm. American Conference of Governmental Industrial Hygienists (ACGIH) adopted Threshold Limit Values (TLVs) for benzene at 0.5 ppm TWA and 2.5 ppm STEL. Toxicology[edit] Biomarkers of exposure[edit] Several tests can determine exposure to benzene. Benzene
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. Most people in developed countries have measureable baseline levels of benzene and other aromatic petroleum hydrocarbons in their blood. 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. 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. 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.[76][77][78][79] Biotransformations[edit] Even if it is not a common substrate for metabolism, benzene can be oxidized by both bacteria and eukaryotes. In bacteria, dioxygenase enzyme can add an oxygen to the ring, and the unstable product is immediately reduced (by NADH) to a cyclic diol with two double bonds, breaking the aromaticity. Next, the diol is newly reduced by NADH
NADH
to catechol. The catechol is then metabolized to acetyl CoA and succinyl CoA, used by organisms mainly in the Krebs Cycle
Krebs Cycle
for energy production. The pathway for the metabolism of benzene is complex and begins in the liver. Several enzymes are involved. These include cytochrome P450 2E1 (CYP2E1), quinine oxidoreductase (NQ01), GSH, and myeloperoxidase (MPO). CYP2E1 is involved at multiple steps: converting benzene to oxepin (benzene oxide), phenol to hydroquinone, and hydroquinone to both benzenetriol and catechol. Hydroquinone, benzenetriol and catechol are converted to polyphenols. In the bone marrow, MPO converts these polyphenols to benzoquinones. 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
DNA
strand breaks, and altering DNA
DNA
methylation (which can affect gene expression). NQ01 and GSH shift metabolism away from toxicity. NQ01 metabolizes benzoquinone toward polyphenols (counteracting the effect of MPO). GSH is involved with the formation of phenylmercapturic acid.[61][80] Genetic polymorphisms in these enzymes may induce loss of function or gain of function. For example, mutations in CYP2E1 increase activity and result in increased generation of toxic metabolites. NQ01 mutations result in loss of function and may result in decreased detoxification. Myeloperoxidase mutations result in loss of function and may result in decreased generation of toxic metabolites. GSH mutations or deletions result in loss of function and result in decreased detoxification. These genes may be targets for genetic screening for susceptibility to benzene toxicity.[81] Molecular toxicology[edit] 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. Glutathione seems to play an important role by protecting against benzene-induced DNA
DNA
breaks and it is being identified as a new biomarker for exposure and effect.[82] Benzene
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. These aberrations can be monitored using fluorescent in situ hybridization (FISH) with DNA
DNA
probes to assess the effects of benzene along with the hematological tests as markers of hematotoxicity.[83] Benzene
Benzene
metabolism involves enzymes coded for by polymorphic genes. Studies have shown that genotype at these loci may influence susceptibility to the toxic effects of benzene exposure. 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.[84] Biological oxidation and carcinogenic activity[edit] One way of understanding the carcinogenic effects of benzene is by examining the products of biological oxidation. Pure benzene, for example, oxidizes in the body to produce an epoxide, benzene oxide, which is not excreted readily and can interact with DNA
DNA
to produce harmful mutations. Routes of exposure[edit] Inhalation[edit] Outdoor air may contain low levels of benzene from automobile service stations, wood smoke, tobacco smoke, the transfer of gasoline, exhaust from motor vehicles, and industrial emissions.[85] About 50% of the entire nationwide (United States) exposure to benzene results from smoking tobacco or from exposure to tobacco smoke.[86] After smoking 32 cigarettes per day, the smoker would take in about 1.8 milligrams (mg) of benzene. This amount is about 10 times the average daily intake of benzene by nonsmokers.[87] Inhaled benzene is primarily expelled unchanged through exhalation. In a human study 16.4 to 41.6% of retained benzene was eliminated through the lungs within five to seven hours after a two- to three-hour exposure to 47 to 110 ppm and only 0.07 to 0.2% of the remaining benzene was excreted unchanged in the urine. After exposure to 63 to 405 mg/m3 of benzene for 1 to 5 hours, 51 to 87% was excreted in the urine as phenol over a period of 23 to 50 hours. In another human study, 30% of absorbed dermally applied benzene, which is primarily metabolized in the liver, was excreted as phenol in the urine.[88] Exposure from soft drinks[edit] Main article: Benzene
Benzene
in soft drinks Under specific conditions and in the presence of other chemicals benzoic acid (a preservative) and ascorbic acid (Vitamin C) may interact to produce benzene. In March 2006, the official Food Standards Agency in Britain conducted a survey of 150 brands of soft drinks. It found that four contained benzene levels above World Health Organization limits. The affected batches were removed from sale. Similar problems were reported by the FDA in the United States.[89] Contamination of water supply[edit] In 2005, the water supply to the city of Harbin
Harbin
in China with a population of almost nine million people, was cut off because of a major benzene exposure. Benzene
Benzene
leaked into the Songhua River, which supplies drinking water to the city, after an explosion at a China National Petroleum
Petroleum
Corporation (CNPC) factory in the city of Jilin on 13 November 2005. See also[edit]

6-membered aromatic rings with one carbon replaced by another group: borabenzene, benzene, silabenzene, germabenzene, stannabenzene, pyridine, phosphorine, arsabenzene, pyrylium salt Industrial Union Department v. American Petroleum
Petroleum
Institute BTEX

References[edit]

^ Lide, D. R., ed. (2005). CRC Handbook of Chemistry and Physics (86th ed.). Boca Raton (FL): CRC Press. ISBN 0-8493-0486-5.  ^ Arnold, D.; Plank, C.; Erickson, E.; Pike, F. (1958). " Solubility
Solubility
of Benzene
Benzene
in Water". Industrial & Engineering Chemistry Chemical & Engineering Data Series. 3 (2): 253–256. doi:10.1021/i460004a016.  ^ Breslow, R.; Guo, T. (1990). "Surface tension measurements show that chaotropic salting-in denaturants are not just water-structure breakers". Proceedings of the National Academy of Sciences of the United States
United States
of America. 87 (1): 167–9. Bibcode:1990PNAS...87..167B. doi:10.1073/pnas.87.1.167. PMC 53221 . PMID 2153285.  ^ Coker, A. Kayode; Ludwig, Ernest E. (2007). Ludwig's Applied Process Design for Chemical And Petrochemical
Petrochemical
Plants. 1. Elsevier. p. 114. ISBN 0-7506-7766-X. Retrieved 2012-05-31.  ^ a b c d e http://chemister.ru/Database/properties-en.php?dbid=1&id=644 ^ a b Atherton Seidell; William F. Linke (1952). Solubilities of Inorganic and Organic Compounds: A Compilation of Solubility
Solubility
Data from the Periodical Literature. Supplement. Van Nostrand.  ^ a b c Benzene
Benzene
in Linstrom, Peter J.; Mallard, William G. (eds.); NIST Chemistry WebBook, NIST Standard Reference Database Number 69, National Institute of Standards and Technology, Gaithersburg (MD), http://webbook.nist.gov (retrieved 2014-05-29) ^ a b c Sigma-Aldrich
Sigma-Aldrich
Co., Benzene. Retrieved on 2014-05-29. ^ a b c "NIOSH Pocket Guide to Chemical Hazards #0049". National Institute for Occupational Safety and Health (NIOSH).  ^ "Benzene". Immediately Dangerous to Life and Health
Immediately Dangerous to Life and Health
Concentrations (IDLH). National Institute for Occupational Safety and Health (NIOSH).  ^ The word "benzoin" is derived from the Arabic expression "luban jawi", or "frankincense of Java". Morris, Edwin T. (1984). Fragrance: The Story of Perfume from Cleopatra to Chanel. Charles Scribner's Sons. p. 101. ISBN 0684181959.  ^ a b Rocke, A. J. (1985). "Hypothesis and Experiment in the Early Development of Kekule's Benzene
Benzene
Theory". Annals of Science. 42 (4): 355–81. doi:10.1080/00033798500200411.  ^ Faraday, M. (1825). "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. 115: 440–466. doi:10.1098/rstl.1825.0022. JSTOR 107752.  On pages 443–450, Faraday discusses "bicarburet of hydrogen" (benzene). On pages 449–450, he shows that benzene's empirical formula is C6H6, although he doesn't realize it because he (like most chemists at that time) used the wrong atomic mass for carbon (6 instead of 12). ^ Kaiser, R. (1968). "Bicarburet of Hydrogen. Reappraisal of the Discovery of Benzene
Benzene
in 1825 with the Analytical Methods of 1968". Angewandte Chemie International Edition in English. 7 (5): 345–350. doi:10.1002/anie.196803451.  ^ Mitscherlich, E. (1834). "Über das Benzol und die Säuren der Oel- und Talgarten" [On benzol and oily and fatty types of acids]. Annalen der Pharmacie. 9 (1): 39–48. doi:10.1002/jlac.18340090103.  In a footnote on page 43, Liebig, the journal's editor, suggested changing Mitscherlich's original name for benzene (namely, "benzin") to "benzol", because the suffix "-in" suggested that it was an alkaloid (e.g., Chinin (quinine)), which benzene isn't, whereas the suffix "-ol" suggested that it was oily, which benzene is. Thus on page 44, Mitscherlich states: "Da diese Flüssigkeit aus der Benzoësäure gewonnen wird, und wahrscheinlich mit den Benzoylverbindungen im Zusammenhang steht, so gibt man ihr am besten den Namen Benzol, da der Name Benzoïn schon für die mit dem Bittermandelöl isomerische Verbindung von Liebig und Wöhler gewählt worden ist." (Since this liquid [benzene] is obtained from benzoic acid and probably is related to benzoyl compounds, the best name for it is "benzol", since the name "benzoïn" has already been chosen, by Liebig and Wöhler, for the compound that's isomeric with the oil of bitter almonds [benzaldehyde].) ^ Laurent, Auguste (1836) "Sur la chlorophénise et les acides chlorophénisique et chlorophénèsique," Annales de Chemie et de Physique, vol. 63, pp. 27–45, see p. 44: "Je donne le nom de phène au radical fondamental des acides précédens (φαινω, j'éclaire), puisque la benzine se trouve dans le gaz de l'éclairage." (I give the name of "phène" (φαινω, I illuminate) to the fundamental radical of the preceding acids, because benzene is found in illuminating gas.) ^ 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. In 1872, Kekulé suggested that benzene had two complementary structures and that these forms rapidly interconverted, so that if there were a double bond between any pair of carbon atoms at one instant, that double bond would become a single bond at the next instant (and vice versa). 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. 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. Thus, a double bond would exist with one neighbor during the first interval and the other neighbor during the next interval. See pages 86–89 of Auguste Kekulé (1872) "Ueber einige Condensationsprodukte des Aldehyds" (On some condensation products of aldehydes), Liebig's Annalen der Chemie und Pharmacie, 162(1): 77–124, 309–320. ^ Hofmann, A. W. (1845) "Ueber eine sichere Reaction auf Benzol" (On a reliable test for benzene), Annalen der Chemie und Pharmacie, vol. 55, pp. 200–205; on pp. 204–205, Hofmann found benzene in coal tar oil. ^ Mansfield Charles Blachford (1849). "Untersuchung des Steinkohlentheers". Annalen der Chemie und Pharmacie. 69: 162–180. doi:10.1002/jlac.18490690203.  ^ Charles Mansfield filed for (November 11, 1847) and received (May 1848) a patent (no. 11,960) for the fractional distillation of coal tar. ^ Hoffman, Augustus W. (1856). "On insolinic acid". Proceedings of the Royal Society. 8: 1–3. doi:10.1098/rspl.1856.0002. The existence and mode of formation of insolinic acid prove that to the series of monobasic aromatic acids, Cn2Hn2-8O4, the lowest known term of which is benzoic acid, … .  [Note: The empirical formulas of organic compounds that appear in Hofmann's article (p. 3) are based upon an atomic mass of carbon of 6 (instead of 12) and an atomic mass of oxygen of 8 (instead of 16).] ^ Cernicharo, José; et al. (1997), "Infrared Space Observatory's Discovery of C4H2, C6H2, and Benzene
Benzene
in CRL 618", Astrophysical Journal Letters, 546 (2): L123–L126, Bibcode:2001ApJ...546L.123C, doi:10.1086/318871  ^ Claus, Adolph K.L. (1867) "Theoretische Betrachtungen und deren Anwendungen zur Systematik der organischen Chemie" (Theoretical considerations and their applications to the classification scheme of organic chemistry), Berichte über die Verhandlungen der Naturforschenden Gesellschaft zu Freiburg im Breisgau (Reports of the Proceedings of the Scientific Society of Freiburg in Breisgau), 4 : 116-381. In the section Aromatischen Verbindungen (aromatic compounds), pp. 315-347, Claus presents Kekulé's hypothetical structure for benzene (p. 317), presents objections to it, presents an alternative geometry (p. 320), and concludes that his alternative is correct (p.326). See also figures on p. 354 or p. 379. ^ Dewar, James (1867) "On the oxidation of phenyl alcohol, and a mechanical arrangement adapted to illustrate structure in the non-saturated hydrocarbons," Proceedings of the Royal Society of Edinburgh 6: 82–86. ^ Ladenburg, Albert (1869) "Bemerkungen zur aromatischen Theorie" (Observations on the aromatic theory), Berichte der Deutschen Chemischen Gesellschaft 2: 140–142. ^ Armstrong, Henry E. (1887) "An explanation of the laws which govern substitution in the case of benzenoid compounds," Journal of the Chemical Society, 51, 258–268; see p. 264. ^ Thiele, Johannes (1899) "Zur Kenntnis der ungesättigten Verbindungen" (On our knowledge of unsaturated compounds), Justus Liebig’s Annalen der Chemie,306: 87–142; see: "VIII. Die aromatischen Verbindungen. Das Benzol." (VIII. The aromatic compounds. Benzene.), pp. 125–129. See further: Thiele (1901) "Zur Kenntnis der ungesättigen Verbindungen," Justus Liebig’s Annalen der Chemie, 319: 129–143. ^ 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". Centric affinities (i.e., bonds) acted within a designated cycle of carbon atoms. From p. 102: " … benzene, according to this view, may be represented by a double ring, in fact." See:

Armstrong, H.E. (1890). "The structure of cycloid hydrocarbons". Proceedings of the Chemical Society. 6: 101–105. 

The use of a circle to denote a benzene nucleus first appeared in:

Armit, James Wilson; Robinson, Robert (1925). "Polynuclear heterocyclic aromatic types. Part II. Some anhydronium bases". Journal of the Chemical Society, Transactions. 127: 1604–1618. doi:10.1039/ct9252701604. 

A history of the determination of benzene's structure is recounted in:

Balaban, Alexandru T.; Schleyer, Paul v. R.; Rzepa, Henry S. (2005). "Crocker, Not Armit and Robinson, Begat the Six Aromatic
Aromatic
Electrons". Chemical Reviews. 105 (10): 3436–3447. doi:10.1021/cr0300946. 

^ J. Loschmidt, Chemische Studien (Vienna, Austria-Hungary: Carl Gerold's Sohn, 1861), pp. 30, 65. ^ Kekulé, F. A. (1865). "Sur la constitution des substances aromatiques". Bulletin de la Societe Chimique de Paris. 3: 98–110.  On p. 100, Kekulé suggests that the carbon atoms of benzene could form a "chaîne fermée" (a closed chain, a loop). ^ Kekulé, F. A. (1866). "Untersuchungen über aromatische Verbindungen (Investigations of aromatic compounds)". Liebigs Annalen der Chemie und Pharmacie. 137 (2): 129–36. doi:10.1002/jlac.18661370202.  ^ Rocke, A. J. (2010) Image and Reality: Kekule, Kopp, and the Scientific Imagination, University of Chicago Press, pp. 186–227, ISBN 0226723356. ^ Read, John (1995). From alchemy to chemistry. New York: Dover Publications. pp. 179–180. ISBN 9780486286907.  ^ English translation Wilcox, David H.; Greenbaum, Frederick R. (1965). "Kekule's benzene ring theory: A subject for lighthearted banter". Journal of Chemical Education. 42 (5): 266–67. Bibcode:1965JChEd..42..266W. doi:10.1021/ed042p266.  ^ Kekulé, F. A. (1890). "Benzolfest: Rede". Berichte der Deutschen Chemischen Gesellschaft. 23: 1302–11. doi:10.1002/cber.189002301204.  ^ Benfey O. T. (1958). " August Kekulé
August Kekulé
and the Birth of the Structural Theory of Organic Chemistry in 1858". Journal of Chemical Education. 35: 21–23. Bibcode:1958JChEd..35...21B. doi:10.1021/ed035p21.  ^ Gillis Jean (1966). "Auguste Kekulé et son oeuvre, réalisée à Gand de 1858 à 1867". Mémoires de la classe des sciences - Académie royale des sciences, des lettres et des beaux-arts de Belgique. 37 (1): 1–40.  ^ Lonsdale, K. (1929). "The Structure of the Benzene
Benzene
Ring in Hexamethylbenzene". Proceedings of the Royal Society. 123A: 494.  ^ Lonsdale, K. (1931). "An X-Ray Analysis of the Structure of Hexachlorobenzene, Using the Fourier Method". Proceedings of the Royal Society. 133A (822): 536–553. Bibcode:1931RSPSA.133..536L. doi:10.1098/rspa.1931.0166.  ^ See:

Wilhelm Körner
Wilhelm Körner
(1867) "Faits pour servir à la détermination du lieu chimique dans la série aromatique" (Facts to be used in determining chemical location in the aromatic series), Bulletins de l'Académie royale des sciences, des lettres et des beaux-arts de Belgique, 2nd series, 24 : 166–185 ; see especially p. 169. From p. 169: "On distingue facilement ces trois séries, dans lesquelles les dérivés bihydroxyliques ont leurs terms correspondants, par les préfixes ortho-, para- et mêta-." (One easily distinguishes these three series – in which the dihydroxy derivatives have their corresponding terms – by the prefixes ortho-, para- and meta-.) Hermann von Fehling, ed., Neues Handwörterbuch der Chemie [New concise dictionary of chemistry] (Braunschweig, Germany: Friedrich Vieweg und Sohn, 1874), vol. 1, p. 1142.

^ Graebe (1869) "Ueber die Constitution des Naphthalins" (On the structure of naphthalene), Annalen der Chemie und Pharmacie, 149 : 20–28 ; see especially p. 26. ^ Victor Meyer (1870) "Untersuchungen über die Constitution der zweifach-substituirten Benzole" (Investigations into the structure of di-substituted benzenes), Annalen der Chemie und Pharmacie, 156 : 265–301 ; see especially pp. 299–300. ^ a b Hillis O. Folkins (2005). "Benzene". Ullmann’s Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a03_475.  ^ Moran D, Simmonett AC, Leach FE, Allen WD, Schleyer PV, Schaefer HF (2006). "Popular Theoretical Methods Predict Benzene
Benzene
and Arenes To Be Nonplanar". Journal of the American Chemical Society. 128 (29): 9342–3. doi:10.1021/ja0630285. PMID 16848464.  ^ Cooper, David L.; Gerratt, Joseph; Raimondi, Mario (1986). "The electronic structure of the benzene molecule". Nature. 323 (6090): 699–701. Bibcode:1986Natur.323..699C. doi:10.1038/323699a0.  ^ Pauling, Linus (1987). "Electronic structure of the benzene molecule". Nature. 325 (6103): 396. Bibcode:1987Natur.325..396P. doi:10.1038/325396d0.  ^ Messmer, Richard P.; Schultz, Peter A. (1987). "The electronic structure of the benzene molecule". Nature. 329 (6139): 492. Bibcode:1987Natur.329..492M. doi:10.1038/329492a0.  ^ Harcourt, Richard D. (1987). "The electronic structure of the benzene molecule". Nature. 329 (6139): 491–492. Bibcode:1987Natur.329..491H. doi:10.1038/329491b0.  ^ " Unicode
Unicode
Character 'BENZENE RING' (U+232C)". fileformat.info. Retrieved 2009-01-16.  ^ " Unicode
Unicode
Character 'BENZENE RING WITH CIRCLE' (U+23E3)". fileformat.info. Retrieved 2009-01-16.  ^ "Heterocyclic Chemistry: Heterocyclic Compounds". Michigan State University, Department of Chemistry.  ^ "Market Study: Benzene
Benzene
(2nd edition), Ceresana, August 2014". ceresana.com. Retrieved 2015-02-10.  ^ "Market Study: Toluene, Ceresana, January 2015". ceresana.com. Retrieved 2015-02-10.  ^ Kolmetz, Gentry, Guidelines for BTX Revamps, AIChE 2007 Spring Conference ^ "Control of Hazardous Air Pollutants From Mobile Sources". U.S. Environmental Protection Agency. 2006-03-29. p. 15853. Archived from the original on 2008-12-05. Retrieved 2008-06-27.  ^ Stranks, D. R.; M. L. Heffernan; K. C. Lee Dow; P. T. McTigue; G. R. A. Withers (1970). Chemistry: A structural view. Carlton, Victoria: Melbourne University Press. p. 347. ISBN 0-522-83988-6.  ^ Welch, Vincent A.; Fallon, Kevin J. and Gelbke, Heinz-Peter (2005) "Ethylbenzene" in Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim, doi:10.1002/14356007.a10_035.pub2 ^ Kasper, Dennis L.et al. (2004) Harrison's Principles of Internal Medicine, 16th ed., McGraw-Hill Professional, p. 618, ISBN 0071402357. ^ Merck Manual, Home Edition, "Overview of Leukemia". ^ Bard, D (2014). "Traffic-related air pollution and the onset of myocardial infarction: disclosing benzene as a trigger? A small-area case-crossover study". PLOS ONE. 9: 6. Bibcode:2014PLoSO...9j0307B. doi:10.1371/journal.pone.0100307. PMC 4059738 . PMID 24932584.  ^ a b Smith, Martyn T. (2010). "Advances in understanding benzene health effects and susceptibility". Annu Rev Public Health. 31: 133–48. doi:10.1146/annurev.publhealth.012809.103646. PMC 4360999 . PMID 20070208.  ^ American Petroleum
Petroleum
Institute, API Toxicological Review, Benzene, September 1948, Agency for Toxic Substances and Disease Registry, Department of Health and Human Services ^ Smith, Martyn T. (2010-01-01). "Advances in Understanding Benzene Health Effects and Susceptibility". Annual Review of Public Health. 31 (1): 133–148. doi:10.1146/annurev.publhealth.012809.103646. PMC 4360999 . PMID 20070208.  ^ WHO. 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 Archived 2008-03-06 at the Wayback Machine., Volumes 1 to 42, Supplement 7 ^ Huff J (2007). "Benzene-induced cancers: abridged history and occupational health impact". Int J Occup Environ Health. 13 (2): 213–21. doi:10.1179/oeh.2007.13.2.213. PMC 3363002 . PMID 17718179.  ^ Rana SV; Verma Y (2005). "Biochemical toxicity of benzene". J Environ Biol. 26 (2): 157–68. PMID 16161967.  ^ Agency for Toxic Substances and Disease Registry. (2007). Benzene: Patient information sheet. ^ Occupational Safety and Health Standards, Toxic and Hazardous Substances, 1910.1028. Osha.gov. Retrieved on 2011-11-23. ^ Public Health Statement for Benzene, Agency for Toxic Substances and Disease Registry. (August 2007). Benzene: Patient information sheet. Atsdr.cdc.gov (2011-03-03). Retrieved on 2011-11-23. ^ Drinking Water
Water
ContaminantsOrganic ChemicalsBenzene. Water.epa.gov. Retrieved on 2014-04-17. ^ Chemical Sampling Information Benzene. Osha.gov. Retrieved on 2011-11-23. ^ Benzene
Benzene
Toxicity: Standards and Regulations ATSDR
ATSDR
– Environmental Medicine & Environmental Health Education – CSEM. Atsdr.cdc.gov (2000-06-30). Retrieved on 2010-10-09. ^ NIOSH respirator selection logic (October 2004). Cincinnati, OH: U.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control, National Institute for Occupational Safety and Health, DHHS (NIOSH). Publication No. 2005-100. ^ Documentation for Immediately Dangerous to Life or Health Concentrations (IDLH): Introduction. Cdc.gov. Retrieved on 2011-11-23. ^ "Public Health Statement for Benzene" U.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control, National Institute for Occupational Safety and Health. Atsdr.cdc.gov (2011-03-03). Retrieved on 2011-11-23. ^ Ashley, DL; Bonin, MA; Cardinali, FL; McCraw, JM; Wooten, JV (1994). "Blood concentrations of volatile organic compounds in a nonoccupationally exposed US population and in groups with suspected exposure" (PDF). Clinical Chemistry. 40 (7 Pt 2): 1401–4. PMID 8013127.  ^ Fustinoni S, Buratti M, Campo L, Colombi A, Consonni D, Pesatori AC, Bonzini M, Farmer P, Garte S, Valerio F, Merlo DF, Bertazzi PA (2005). "Urinary t,t-muconic acid, S-phenylmercapturic acid and benzene as biomarkers of low benzene exposure". Chemico-biological interactions. 153–154: 253–6. doi:10.1016/j.cbi.2005.03.031. PMID 15935823.  ^ ACGIH (2009). 2009 TLVs and BEIs. American Conference of Governmental Industrial Hygienists, Cincinnati, Ohio. ^ Baselt, R. (2008) Disposition of Toxic Drugs and Chemicals in Man, 8th edition, Biomedical Publications, Foster City, CA, pp. 144–148, ISBN 0962652377. ^ Snyder, R; Hedli, C.C. (1996). "An overview of benzene metabolism". Environ Health Perspect. 104 (Suppl 6): 1165–1171. doi:10.1289/ehp.96104s61165. PMC 1469747 . PMID 9118888.  ^ Dougherty, D; Garte, S; Barchowsky, A; Zmuda, J; Taioli, E (2008). "NQO1, MPO, CYP2E1, GSTT1 and STM1 polymorphisms and biological effects of benzene exposure—a literature review". Toxicology Letters. 182 (1–3): 7–17. doi:10.1016/j.toxlet.2008.09.008. PMID 18848868.  ^ Fracasso ME, Doria D, Bartolucci GB, Carrieri M, Lovreglio P, Ballini A, Soleo L, Tranfo G, Manno M (2010). "Low air levels of benzene: Correlation between biomarkers of exposure and genotoxic effects". Toxicol Lett. 192 (1): 22–8. doi:10.1016/j.toxlet.2009.04.028. PMID 19427373.  ^ Eastmond, D.A.; Rupa, DS; Hasegawa, LS (2000). "Detection of hyperdiploidy and chromosome breakage in interphase human lymphocytes following exposure to the benzene metabolite hydroquinone using multicolor fluorescence in situ hybridization with DNA
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Benzene
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at The Periodic Table of Videos
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v t e

Annulenes

Even–numbered

Cyclobutadiene Benzene Cyclooctatetraene Cyclodecapentaene Cyclododecahexaene Cyclotetradecaheptaene Cyclohexadecaoctaene Cyclooctadecanonaene

Odd–numbered

Cyclopropene Cyclopentadiene Cycloheptatriene Cyclononatetraene

Compounds in italics are aromatic

v t e

Cycloalkenes

Alkenes

Cyclopropene Cyclobutene Cyclopentene Cyclohexene Cycloheptene Cyclooctene Cyclononene

Dienes

Cyclobutadiene Cyclopentadiene Cyclohexadiene

1,3-Cyclohexadiene 1,4-Cyclohexadiene

Cycloheptadiene

1,3-Cycloheptadiene 1,4-Cycloheptadiene

Cyclooctadiene

1,5-Cyclooctadiene

Trienes

Benzene Cycloheptatriene

Tetraenes

Cyclooctatetraene Cyclononatetraene

v t e

Hydrocarbons

Saturated aliphatic hydrocarbons

Alkanes CnH2n + 2

Linear alkanes

Methane Ethane Propane Butane Pentane Hexane Heptane Octane Nonane Decane

Branched alkanes

Isobutane Isopentane 3-Methylpentane Neopentane Isohexane Isoheptane Isooctane Isononane Isodecane

Cycloalkanes

Cyclopropane Cyclobutane Cyclopentane Cyclohexane Cycloheptane Cyclooctane Cyclononane Cyclodecane

Alkylcycloalkanes

Methylcyclopropane Methylcyclobutane Methylcyclopentane Methylcyclohexane Isopropylcyclohexane

Bicycloalkanes

Housane
Housane
(bicyclo[2.1.0]pentane) Norbornane
Norbornane
(bicyclo[2.2.1]heptane) Decalin
Decalin
(bicyclo[4.4.0]decane)

Polycycloalkanes

Adamantane Diamondoid Perhydrophenanthrene Sterane Cubane Prismane Dodecahedrane Basketane Churchane Pagodane Twistane

Other

Spiroalkanes

Unsaturated aliphatic hydrocarbons

Alkenes CnH2n

Linear alkenes

Ethene Propene Butene Pentene Hexene Heptene Octene Nonene Decene

Branched alkenes

Isobutene Isopentene Neopentene Isohexene Isoheptene Isooctene Isononene Isodecene

Alkynes CnH2n − 2

Linear alkynes

Ethyne Propyne Butyne Pentyne Hexyne Heptyne Octyne Nonyne Decyne

Branched alkynes

Isobutyne Isopentyne Neopentyne Isohexyne Isoheptyne Isooctyne Isononyne Isodecyne

Cycloalkenes

Cyclopropene Cyclobutene Cyclopentene Cyclohexene Cycloheptene Cyclooctene Cyclononene Cyclodecene

Alkyilcycloalkenes

Methylcyclopropene Methylcyclobutene Methylcyclopentene Methylcyclohexene Isopropylcyclohexene

Bicycloalkenes

Norbornene

Cycloalkynes

Cyclopropyne Cyclobutyne Cyclopentyne Cyclohexyne Cycloheptyne Cycloctyne Cyclononyne Cyclodecyne

Alkadienes

Propadiene Butadiene Pentadiene Hexadiene Heptadiene Octadiene Nonadiene Decadiene

Other

Alkatriene Alkadiyne Cumulene Cyclooctatetraene Cyclododecatriene Enyne

Aromatic hydrocarbons

PAHs

Acenes

Naphthalene Anthracene Naphthacene Pentacene Hexacene Heptacene

Other

Azulene Fluorene Helicenes Circulenes

Alkylbenzenes

Toluene Xylene Ethylbenzene Cumene Styrene Mesitylene Pseudocumene Hexamethylbenzene

Other

Benzene Phenanthrene Chrysene Pyrene Corannulene Kekulene

Other

Annulenes Annulynes Alicyclic compounds

v t e

Functional groups

Only carbon, hydrogen and oxygen

Hydrocarbons

Allene Alkene
Alkene
(Allyl, Vinyl) Alkyl
Alkyl
(Methyl, Ethyl, Propyl, Butyl, Pentyl) Alkyne Benzyl Carbene Cumulene Methylene bridge Methylene group Methine Phenyl

Other

Acetoxy Acetyl Acryloyl Acyl Aldehyde Alkoxy (Methoxy) Benzoyl Carbonyl Carboxyl Dioxirane Epoxide Ester Ether Ethylenedioxy Hydroxy Ketone Methylenedioxy Peroxide
Peroxide
(Organic) Ynone

Only one element apart from C, H, O

Nitrogen

Amine Azo compound Cyanate Hydrazone Imide Imine Isocyanate Isonitrile Nitrene Nitrile Nitro compound Nitroso
Nitroso
compound Organic amide Oxime

Phosphorus

Phosphonate Phosphonous

Sulfur

Disulfide Sulfone Sulfonic acid Sulfoxide Thial Thioester Thioether Thioketone Thiol

Selenium

Selenol Selenonic acid Seleninic acid Selenenic acid

Tellurium

Tellurol

Other

Isothiocyanate Phosphoramide Sulfenyl chloride Sulfonamide Thiocyanate

See also chemical classification, chemical nomenclature (inorganic, organic)

v t e

GABAA receptor positive modulators

Alcohols

Brometone Butanol Chloralodol Chlorobutanol
Chlorobutanol
(cloretone) Ethanol
Ethanol
(alcohol) (alcoholic drink) Ethchlorvynol Isobutanol Isopropanol Menthol Methanol Methylpentynol Pentanol Petrichloral Propanol tert-Butanol (2M2P) tert-Pentanol (2M2B) Tribromoethanol Trichloroethanol Triclofos Trifluoroethanol

Barbiturates

(-)-DMBB Allobarbital Alphenal Amobarbital Aprobarbital Barbexaclone Barbital Benzobarbital Benzylbutylbarbiturate Brallobarbital Brophebarbital Butabarbital/Secbutabarbital Butalbital Buthalital Butobarbital Butallylonal Carbubarb Crotylbarbital Cyclobarbital Cyclopentobarbital Difebarbamate Enallylpropymal Ethallobarbital Eterobarb Febarbamate Heptabarb Heptobarbital Hexethal Hexobarbital Metharbital Methitural Methohexital Methylphenobarbital Narcobarbital Nealbarbital Pentobarbital Phenallymal Phenobarbital Phetharbital Primidone Probarbital Propallylonal Propylbarbital Proxibarbital Reposal Secobarbital Sigmodal Spirobarbital Talbutal Tetrabamate Tetrabarbital Thialbarbital Thiamylal Thiobarbital Thiobutabarbital Thiopental Thiotetrabarbital Valofane Vinbarbital Vinylbital

Benzodiazepines

2-Oxoquazepam 3-Hydroxyphenazepam Adinazolam Alprazolam Arfendazam Avizafone Bentazepam Bretazenil Bromazepam Brotizolam Camazepam Carburazepam Chlordiazepoxide Ciclotizolam Cinazepam Cinolazepam Clazolam Climazolam Clobazam Clonazepam Clonazolam Cloniprazepam Clorazepate Clotiazepam Cloxazolam CP-1414S Cyprazepam Delorazepam Demoxepam Diazepam Diclazepam Doxefazepam Elfazepam Estazolam Ethyl carfluzepate Ethyl dirazepate Ethyl loflazepate Etizolam EVT-201 FG-8205 Fletazepam Flubromazepam Flubromazolam Fludiazepam Flunitrazepam Flunitrazolam Flurazepam Flutazolam Flutemazepam Flutoprazepam Fosazepam Gidazepam Halazepam Haloxazolam Iclazepam Imidazenil Irazepine Ketazolam Lofendazam Lopirazepam Loprazolam Lorazepam Lormetazepam Meclonazepam Medazepam Menitrazepam Metaclazepam Mexazolam Midazolam Motrazepam N-Desalkylflurazepam Nifoxipam Nimetazepam Nitrazepam Nitrazepate Nitrazolam Nordazepam Nortetrazepam Oxazepam Oxazolam Phenazepam Pinazepam Pivoxazepam Prazepam Premazepam Proflazepam Pyrazolam QH-II-66 Quazepam Reclazepam Remimazolam Rilmazafone Ripazepam Ro48-6791 Ro48-8684 SH-053-R-CH3-2′F Sulazepam Temazepam Tetrazepam Tolufazepam Triazolam Triflubazam Triflunordazepam
Triflunordazepam
(Ro5-2904) Tuclazepam Uldazepam Zapizolam Zolazepam Zomebazam

Carbamates

Carisbamate Carisoprodol Clocental Cyclarbamate Difebarbamate Emylcamate Ethinamate Febarbamate Felbamate Hexapropymate Lorbamate Mebutamate Meprobamate Nisobamate Pentabamate Phenprobamate Procymate Styramate Tetrabamate Tybamate

Flavonoids

6-Methylapigenin Ampelopsin
Ampelopsin
(dihydromyricetin) Apigenin Baicalein Baicalin Catechin EGC EGCG Hispidulin Linarin Luteolin Rc-OMe Skullcap constituents (e.g., baicalin) Wogonin

Imidazoles

Etomidate Metomidate Propoxate

Kava
Kava
constituents

10-Methoxyyangonin 11-Methoxyyangonin 11-Hydroxyyangonin Desmethoxyyangonin 11-Methoxy-12-hydroxydehydrokavain 7,8-Dihydroyangonin Kavain 5-Hydroxykavain 5,6-Dihydroyangonin 7,8-Dihydrokavain 5,6,7,8-Tetrahydroyangonin 5,6-Dehydromethysticin Methysticin 7,8-Dihydromethysticin Yangonin

Monoureides

Acecarbromal Apronal
Apronal
(apronalide) Bromisoval Carbromal Capuride Ectylurea

Neuroactive steroids

Acebrochol Allopregnanolone
Allopregnanolone
(brexanolone) Alfadolone Alfaxalone 3α-Androstanediol Androstenol Androsterone Certain anabolic-androgenic steroids Cholesterol DHDOC 3α-DHP 5α-DHP 5β-DHP DHT Etiocholanolone Ganaxolone Hydroxydione Minaxolone ORG-20599 ORG-21465 P1-185 Pregnanolone
Pregnanolone
(eltanolone) Progesterone Renanolone SAGE-105 SAGE-217 SAGE-324 SAGE-516 SAGE-689 SAGE-872 Testosterone THDOC

Nonbenzodiazepines

β-Carbolines: Abecarnil Gedocarnil Harmane SL-651,498 ZK-93423

Cyclopyrrolones: Eszopiclone Pagoclone Pazinaclone Suproclone Suriclone Zopiclone

Imidazopyridines: Alpidem DS-1 Necopidem Saripidem Zolpidem

Pyrazolopyrimidines: Divaplon Fasiplon Indiplon Lorediplon Ocinaplon Panadiplon Taniplon Zaleplon

Others: Adipiplon CGS-8216 CGS-9896 CGS-13767 CGS-20625 CL-218,872 CP-615,003 CTP-354 ELB-139 GBLD-345 Imepitoin JM-1232 L-838,417 Lirequinil
Lirequinil
(Ro41-3696) NS-2664 NS-2710 NS-11394 Pipequaline ROD-188 RWJ-51204 SB-205,384 SX-3228 TGSC01AA TP-003 TPA-023 TP-13 U-89843A U-90042 Viqualine Y-23684

Phenols

Fospropofol Propofol Thymol

Piperidinediones

Glutethimide Methyprylon Piperidione Pyrithyldione

Pyrazolopyridines

Cartazolate Etazolate ICI-190,622 Tracazolate

Quinazolinones

Afloqualone Cloroqualone Diproqualone Etaqualone Mebroqualone Mecloqualone Methaqualone Methylmethaqualone Nitromethaqualone SL-164

Volatiles/gases

Acetone Acetophenone Acetylglycinamide chloral hydrate Aliflurane Benzene Butane Butylene Centalun Chloral Chloral
Chloral
betaine Chloral
Chloral
hydrate Chloroform Cryofluorane Desflurane Dichloralphenazone Dichloromethane Diethyl ether Enflurane Ethyl chloride Ethylene Fluroxene Gasoline Halopropane Halothane Isoflurane Kerosine Methoxyflurane Methoxypropane Nitric oxide Nitrogen Nitrous oxide Norflurane Paraldehyde Propane Propylene Roflurane Sevoflurane Synthane Teflurane Toluene Trichloroethane (methyl chloroform) Trichloroethylene Vinyl ether

Others/unsorted

3-Hydroxybutanal α-EMTBL AA-29504 Avermectins (e.g., ivermectin) Bromide compounds (e.g., lithium bromide, potassium bromide, sodium bromide) Carbamazepine Chloralose Chlormezanone Clomethiazole DEABL Dihydroergolines (e.g., dihydroergocryptine, dihydroergosine, dihydroergotamine, ergoloid (dihydroergotoxine)) DS2 Efavirenz Etazepine Etifoxine Fenamates (e.g., flufenamic acid, mefenamic acid, niflumic acid, tolfenamic acid) Fluoxetine Flupirtine Hopantenic acid Lanthanum Lavender oil Lignans (e.g., 4-O-methylhonokiol, honokiol, magnolol, obovatol) Loreclezole Menthyl isovalerate
Menthyl isovalerate
(validolum) Monastrol Niacin Nicotinamide
Nicotinamide
(niacinamide) Org 25,435 Phenytoin Propanidid Retigabine
Retigabine
(ezogabine) Safranal Seproxetine Stiripentol Sulfonylalkanes (e.g., sulfonmethane (sulfonal), tetronal, trional) Terpenoids (e.g., borneol) Topiramate Valerian constituents (e.g., isovaleric acid, isovaleramide, valerenic acid, valerenol)

Unsorted benzodiazepine site positive modulators: α-Pinene MRK-409 (MK-0343) TCS-1105 TCS-1205

See also: Receptor/signaling modulators • GABA receptor modulators • GABA metabolism/transport modulators

v t e

Molecules detected in outer space

Molecules

Diatomic

Aluminium monochloride Aluminium monofluoride Aluminium monoxide Argonium Carbon
Carbon
monophosphide Carbon
Carbon
monosulfide Carbon
Carbon
monoxide Carborundum Cyanogen
Cyanogen
radical Diatomic carbon Fluoromethylidynium Hydrogen
Hydrogen
chloride Hydrogen
Hydrogen
fluoride Hydrogen
Hydrogen
(molecular) Hydroxyl radical Iron(II) oxide Magnesium monohydride cation Methylidyne radical Nitric oxide Nitrogen
Nitrogen
(molecular) Nitrogen
Nitrogen
monohydride Nitrogen
Nitrogen
sulfide Oxygen
Oxygen
(molecular) Phosphorus monoxide Phosphorus mononitride Potassium chloride Silicon carbide Silicon mononitride Silicon monoxide Silicon monosulfide Sodium chloride Sodium iodide Sulfur monohydride Sulfur monoxide Titanium oxide

Triatomic

Aluminium hydroxide Aluminium isocyanide Amino radical Carbon
Carbon
dioxide Carbonyl sulfide CCP radical Chloronium Diazenylium Dicarbon monoxide Disilicon carbide Ethynyl radical Formyl radical Hydrogen
Hydrogen
cyanide (HCN) Hydrogen
Hydrogen
isocyanide (HNC) Hydrogen
Hydrogen
sulfide Hydroperoxyl Iron cyanide Isoformyl Magnesium cyanide Magnesium isocyanide Methylene radical N2H+ Nitrous oxide Nitroxyl Ozone Phosphaethyne Potassium cyanide Protonated molecular hydrogen Sodium cyanide Sodium hydroxide Silicon carbonitride c-Silicon dicarbide Silicon naphthalocyanine Sulfur dioxide Thioformyl Thioxoethenylidene Titanium dioxide Tricarbon Water

Four atoms

Acetylene Ammonia Cyanic acid Cyanoethynyl Cyclopropynylidyne Formaldehyde Fulminic acid HCCN Hydrogen
Hydrogen
peroxide Hydromagnesium isocyanide Isocyanic acid Isothiocyanic acid Ketenyl Methylene amidogen Methyl radical Propynylidyne Protonated carbon dioxide Protonated hydrogen cyanide Silicon tricarbide Thioformaldehyde Tricarbon
Tricarbon
monoxide Tricarbon
Tricarbon
sulfide Thiocyanic acid

Five atoms

Ammonium
Ammonium
ion Butadiynyl Carbodiimide Cyanamide Cyanoacetylene Cyanoformaldehyde Cyanomethyl Cyclopropenylidene Formic acid Isocyanoacetylene Ketene Methane Methoxy
Methoxy
radical Methylenimine Propadienylidene Protonated formaldehyde Protonated formaldehyde Silane Silicon-carbide cluster

Six atoms

Acetonitrile Cyanobutadiynyl radical E-Cyanomethanimine Cyclopropenone Diacetylene Ethylene Formamide HC4N Ketenimine Methanethiol Methanol Methyl isocyanide Pentynylidyne Propynal Protonated cyanoacetylene

Seven atoms

Acetaldehyde Acrylonitrile

Vinyl cyanide

Cyanodiacetylene Ethylene
Ethylene
oxide Hexatriynyl radical Methylacetylene Methylamine Methyl isocyanate Vinyl alcohol

Eight atoms

Acetic acid Aminoacetonitrile Cyanoallene Ethanimine Glycolaldehyde Heptatrienyl radical Hexapentaenylidene Methylcyanoacetylene Methyl formate Propenal

Nine atoms

Acetamide Cyanohexatriyne Cyanotriacetylene Dimethyl ether Ethanol Methyldiacetylene Octatetraynyl radical Propene Propionitrile

Ten atoms or more

Acetone Benzene Benzonitrile Buckminsterfullerene
Buckminsterfullerene
(C60 fullerene, buckyball) C70 fullerene Cyanodecapentayne Cyanopentaacetylene Cyanotetra-acetylene Ethylene
Ethylene
glycol Ethyl formate Methyl acetate Methyl-cyano-diacetylene Methyltriacetylene Propanal n-Propyl cyanide Pyrimidine

Deuterated molecules

Ammonia Ammonium
Ammonium
ion Formaldehyde Formyl radical Heavy water Hydrogen
Hydrogen
cyanide Hydrogen
Hydrogen
deuteride Hydrogen
Hydrogen
isocyanide Methylacetylene N2D+ Trihydrogen cation

Unconfirmed

Anthracene Dihydroxyacetone Ethyl methyl ether Glycine Graphene H2NCO+ Linear C5 Naphthalene
Naphthalene
cation Phosphine Pyrene Silylidine

Related

Abiogenesis Astrobiology Astrochemistry Atomic and molecular astrophysics Chemical formula Circumstellar envelope Cosmic dust Cosmic ray Cosmochemistry Diffuse interstellar band Earliest known life forms Extraterrestrial life Extraterrestrial liquid water Forbidden mechanism Helium hydride ion Homochirality Intergalactic dust Interplanetary medium Interstellar medium Photodissociation region Iron–sulfur world theory Kerogen Molecules in stars Nexus for Exoplanet System Science Organic compound Outer space PAH world hypothesis Panspermia Polycyclic aromatic hydrocarbon
Polycyclic aromatic hydrocarbon
(PAH) RNA world hypothesis Spectroscopy Tholin

Book:Chemistry Category:Astrochemistry Category:Molecules Portal:Astrobiology Portal:Astronomy Portal:Chemistry

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LCCN: sh85013229 GND: 41445

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