From Wikipedia, the free encyclopedia
| Benzene |
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other names
Benzol
cyclohexa-1,3,5-triene
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| Identifiers |
| CAS number |
71-43-2  Y |
| PubChem |
241 |
| ChemSpider |
236 |
| RTECS number |
CY1400000 |
| SMILES |
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| InChI |
1/C6H6/c1-2-4-6-5-3-1/h1-6H
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| InChI key |
UHOVQNZJYSORNB-UHFFFAOYAH |
| Properties |
| Molecular formula |
C6H6 |
| Molar mass |
78.11 g mol−1 |
| Appearance |
Colorless liquid |
| Density |
0.8765(20) g/cm3 [1] |
| Melting point |
5.5 °C, 279 K, 42 °F
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| Boiling point |
80.1 °C, 353 K, 176 °F
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| Solubility in water |
0.8 g/L (15 °C) |
| Viscosity |
0.652 cP at 20 °C |
| Dipole moment |
0 D |
| Hazards |
| MSDS |
External MSDS |
| EU classification |
Flammable (F)
Carc. Cat. 1
Muta. Cat. 2
Toxic (T) |
| R-phrases |
R45, R46, R11, R36/38,R48/23/24/25, R65 |
| S-phrases |
S53, S45 |
| NFPA 704 |
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| Flash point |
−11 °C |
| Related compounds |
| Related compounds |
toluene
borazine |
| Supplementary data page |
Structure and
properties |
n, εr, etc. |
Thermodynamic
data |
Phase behaviour
Solid, liquid, gas |
| Spectral data |
UV, IR, NMR, MS |
 Y (what is this?) (verify)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) |
| Infobox references |
.^ Benzene , or Benzol (see also Benzine ) is an organic chemical compound with the formula C 6 H 6 .- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
^ At present, such uses are minimal; most benzene is consumed in the chemical industry as a raw material for numerous organic chemicals and in plastics manufacture.- Notice of Intended Changes - Benzene 10 February 2010 12:012 UTC tobaccodocuments.org [Source type: Academic]
^ Benzene (CAS Registry Number 71-43-2) is a simple cyclic organic compound with molecular formula C 6 H 6 .- Page 4 - Canadian Environmental Protection Act: Priority Substances List Report: Benzene 10 February 2010 12:012 UTC www.hc-sc.gc.ca [Source type: Academic]
.^ Benzene is highly flammable.- Benzene and Human Health 10 February 2010 12:012 UTC geosalud.com [Source type: FILTERED WITH BAYES]
^ At room temperature, benzene is a clear, colorless-to-light yellow liquid that is highly flammable.- ATSDR - MMG: Benzene 10 February 2010 12:012 UTC www.atsdr.cdc.gov [Source type: Academic]
^ Benzene is also a highly flammable liquid.- Benzene Safety Program - OSHA 29 CFR 1910.1028, 29 CFR 1010.1000, 29 CFR 1910.1200, 29 CFR 1910.132-138 10 February 2010 12:012 UTC www.safetyinstruction.com [Source type: FILTERED WITH BAYES]
.^ It is carcinogenic and its use as an additive in gasoline is now limited, but it is an important industrial solvent and precursor in the production of drugs, plastics , synthetic rubber , and dyes .- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
^ It is an important industrial solvent and precursor in the production of drugs, plastics, gasoline, synthetic rubber, and dyes.
^ Gasoline (benzene is used as an additive) .
.^ Benzene is obtained from crude petroleum.- ATSDR - MMG: Benzene 10 February 2010 12:012 UTC www.atsdr.cdc.gov [Source type: Academic]
^ Benzene is also present in crude oil and gasoline and cigarette smoke.- Benzene and Human Health 10 February 2010 12:012 UTC geosalud.com [Source type: FILTERED WITH BAYES]
^ Benzene also is a natural part of crude oil, gasoline, and cigarette smoke.
.^ After the simplest possible aromatic hydrocarbon, benzene, such a configuration of six carbon atoms is known as a benzene ring.
^ It may also contain the aromatic hydrocarbons benzene, toluene, mixed xylenes and ethylbenzene.
^ Refinery hydrocarbon streams containing benzene often contain additional aromatic compounds having a high octane value, such as toluene, ethylbenzene, and the like.- PROCESS FOR BENZENE REMOVAL FROM GASOLINE - Patent application 10 February 2010 12:012 UTC www.faqs.org [Source type: Reference]
.^ Accordingly, the instant invention relates to a hexa-carboxyphenylbenzene compound of the structural formula ##STR4## wherein R is selected from the group consisting of hydrogen, alkyl moieties, and aryl moieties.- Hexa(meta-,para-carboxyphenyl)benzene compounds - US4339595 10 February 2010 12:012 UTC www.patents.com [Source type: Reference]
^ Its chemical structure consists of a benzene ring substituted with a hydroxy group and a propenyl group.
^ Interest in the fullerenes has led to the discovery of a related group of carbon structures referred to as nanotubes.- Chemical Reactivity 10 February 2010 12:012 UTC www.cem.msu.edu [Source type: Reference]
History
Discovery
.^ The word "benzene" derives historically from "gum benzoin", sometimes called "benjamin" (i.e., benzoin resin), an aromatic resin known to European pharmacists and perfumers since the 15th century as a product of southeast Asia.- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
^ During 1967, there was about 800 million gallons of benzene produced in the U.S., and by 1969, the amount of benzene increased to 1,185 million gallons with approximately 16% of the productions derived from coal.
^ After the simplest possible aromatic hydrocarbon, benzene, such a configuration of six carbon atoms is known as a benzene ring.
"Benzoin" is itself a corruption of the Arabic expression "luban jawi," or "
frankincense of
Java." An acidic material was derived from benzoin by sublimation, and named "flowers of benzoin," or benzoic acid.
.^ If the substrate is a very reactive benzene derivative, such as anisole, carboxylic esters or acids may be the source of the acylating electrophile.- Aromatic Reactivity 10 February 2010 12:012 UTC www.cem.msu.edu [Source type: Academic]
^ In the reforming processing, C 6 cycloparaffins and other higher boiling cyclic hydrocarbons are converted to benzene and benzene derivatives.- Isomerization of Benzene-Containing Feedstocks - Patent application 10 February 2010 12:012 UTC www.faqs.org [Source type: Reference]
^ Encyclopedia - Anthracene In chemistry, anthracene is a solid polycyclic aromatic hydrocarbon consisting of three benzene rings derived from coal-tar.
[2]
.^ Faraday first isolated benzene in 1825 from the oily residue derived from the production of illuminating gas, giving it the name bicarburet of hydrogen .- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
^ Benzene was first discovered and isolated from coal tar in the 1800s.- Benzene and Human Health 10 February 2010 12:012 UTC geosalud.com [Source type: FILTERED WITH BAYES]
^ Benzene can enter the environment from any stage involved in production, storage, use, and transport of isolated benzene, and crude oil and gasoline, including emissions resulting from fuel combustion.- Page 4 - Canadian Environmental Protection Act: Priority Substances List Report: Benzene 10 February 2010 12:012 UTC www.hc-sc.gc.ca [Source type: Academic]
[3][4] .^ In 1833, Eilhard Mitscherlich produced it via the distillation of benzoic acid (from gum benzoin) and lime .- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
^ An acidic material was derived from benzoin by sublimation, and named "flowers of benzoin," or benzoic acid.- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
^ However, an alkylbenzene, toluene for example, undergoes oxidation in the body to produce benzoic acid.- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
.^ Mitscherlich gave the compound the name benzin .- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
[5] .^ In 1836 the French chemist Auguste Laurent named the substance "phène"; this is the root of the word phenol , which is hydroxylated benzene, and phenyl, which is the radical formed by abstraction of a hydrogen atom from benzene.- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
^ In 1865 the German chemist Friedrich August Kekulé published a paper in French (for he was then teaching in Francophone Belgium) suggesting that the structure contained a six-membered ring of carbon atoms with alternating single and double bonds.- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
^ Gradually the sense developed among chemists that substances related to benzene formed a natural chemical family.- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
.^ Benzene was first discovered and isolated from coal tar in the 1800s.- Benzene and Human Health 10 February 2010 12:012 UTC geosalud.com [Source type: FILTERED WITH BAYES]
^ In 1845, Charles Mansfield, working under August Wilhelm von Hofmann , isolated benzene from coal tar .- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
^ Encyclopedia - Anthracene In chemistry, anthracene is a solid polycyclic aromatic hydrocarbon consisting of three benzene rings derived from coal-tar.
.^ Benzene was first discovered and isolated from coal tar in the 1800s.- Benzene and Human Health 10 February 2010 12:012 UTC geosalud.com [Source type: FILTERED WITH BAYES]
^ Four years later, Mansfield began the first industrial-scale production of benzene, based on the coal-tar method.- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
^ During 1967, there was about 800 million gallons of benzene produced in the U.S., and by 1969, the amount of benzene increased to 1,185 million gallons with approximately 16% of the productions derived from coal.
.^ Gradually the sense developed among chemists that substances related to benzene formed a natural chemical family.- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
^ In 1836 the French chemist Auguste Laurent named the substance "phène"; this is the root of the word phenol , which is hydroxylated benzene, and phenyl, which is the radical formed by abstraction of a hydrogen atom from benzene.- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
^ The plaintiffs are stating that employees are still being put at risk and could develop a benzene-related illness similar to what their father did.
.^ In 1855 August Wilhelm Hofmann used the word " aromatic " to designate this family relationship, after a characteristic property of many of its members.- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
^ In 1845, Charles Mansfield, working under August Wilhelm von Hofmann , isolated benzene from coal tar .- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
^ Aromatic hydrocarbon - Models of benzene ring electron configurations Aromatic hydrocarbon - Properties of aromatic hydrocarbons Aromatic hydrocarbon - Members of this group of substances Aromatic hydrocarbon - PAHs .
Ring formula
.^ The empirical formula for benzene was long known, but its highly polyunsaturated structure was challenging to determine.- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
^ What is the empirical formula for benzene?
^ To reflect the delocalised nature of the bonding, benzene is often depicted with a circle inside a hexagonal arrangement of carbon atoms: .- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
.^ Because of the low hydrogen to carbon ratio in this and other aromatic compounds (note that the H:C ratio in an alkane is > 2), chemists expected their structural formulas would contain a large number of double or triple bonds.- Chemical Reactivity 10 February 2010 12:012 UTC www.cem.msu.edu [Source type: Reference]
^ The sp 2 hybridized ring atoms are connected by brown bonds, the π-electron pairs and bonds that constitute the aromatic ring are colored blue.- Chemical Reactivity 10 February 2010 12:012 UTC www.cem.msu.edu [Source type: Reference]
^ After the simplest possible aromatic hydrocarbon, benzene, such a configuration of six carbon atoms is known as a benzene ring.
.^ In 1865 the German chemist Friedrich August Kekulé published a paper in French (for he was then teaching in Francophone Belgium) suggesting that the structure contained a six-membered ring of carbon atoms with alternating single and double bonds.- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
^ Archibald Scott Couper in 1858 and Joseph Loschmidt in 1861 suggested possible structures that contained multiple double bonds or multiple rings, but the study of aromatic compounds was in its very early years, and too little evidence was then available to help chemists decide on any particular structure.- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
^ In 1836 the French chemist Auguste Laurent named the substance "phène"; this is the root of the word phenol , which is hydroxylated benzene, and phenyl, which is the radical formed by abstraction of a hydrogen atom from benzene.- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
.^ The next year he published a much longer paper in German on the same subject.- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
[6][7] .^ 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 diderivative—to argue in support of his proposed structure.- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
^ If we use the nitration of benzene as a reference, we can assign the rate of reaction at one of the carbons to be 1.0.- Aromatic Reactivity 10 February 2010 12:012 UTC www.cem.msu.edu [Source type: Academic]
^ Major Uses and Sources of ®ccupational Exposure At one time, benzene was an important solvent.- Notice of Intended Changes - Benzene 10 February 2010 12:012 UTC tobaccodocuments.org [Source type: Academic]
.^ Kekulé's symmetrical ring could explain these curious facts.- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
^ While it is true that these findings are in agreement with previous studies(29) they still could not explain the 43% of the patients who were not exposed, and still had abnormal chromosomal changes.- Benzene and Diseases of the Blood: Potential Industrial Exposures 10 February 2010 12:012 UTC www.environmentaldiseases.com [Source type: Academic]
^ Under these conditions, aliphatic hydrocarbons form rings and lose hydrogen to become aromatic hydrocarbons.- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
.^ Benzene is the archetypical aromatic compound.- Chemical Reactivity 10 February 2010 12:012 UTC www.cem.msu.edu [Source type: Reference]
^ 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.- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
^ Encyclopedia - Aniline Aniline, phenylamine or aminobenzene (C6H5NH2) is an organic chemical compound which is a primary aromatic amine consisting of a benzene ring and an amino group.
.^ Here Kekulé spoke of the creation of the theory.- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
.^ 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).- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
^ How Sleep Improves Memory And Cultivates Genius - Huffington Post (blog) How Sleep Improves Memory And Cultivates GeniusHuffington Post (blog)Kekule and his 19th century chemists wrestled with the structure of benzene until Kekule fell asleep to dream of a snake eating its own tail.- Benzene Exposure Benzene Lawyer Lawsuit Benzene Cancer Attorney Leukemia Law Firm 10 February 2010 12:012 UTC www.thepicenter.com [Source type: General]
^ (PCBs) are a class of organic compounds with 1 to 10 chlorine atoms attached to biphenyl, which is a molecule composed of two benzene rings.- Benzene Exposure Benzene Lawyer Lawsuit Benzene Cancer Attorney Leukemia Law Firm 10 February 2010 12:012 UTC www.thepicenter.com [Source type: General]
.^ This vision, he said, came to him after years of studying the nature of carbon-carbon bonds.- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
^ To reflect the delocalised nature of the bonding, benzene is often depicted with a circle inside a hexagonal arrangement of carbon atoms: .- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
^ This was 20 years after he had solved the problem of how carbon atoms could bond to up to four other atoms at the same time.- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
.^ This was 20 years after he had solved the problem of how carbon atoms could bond to up to four other atoms at the same time.- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
^ To reflect the delocalised nature of the bonding, benzene is often depicted with a circle inside a hexagonal arrangement of carbon atoms: .- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
^ Using X-ray diffraction, researchers discovered that all of the carbon-carbon bonds in benzene are of the same length of 140 picometres (pm).- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
.^ Berichte der Deutschen Chemischen Gesellschaft 23 : 1302–11.- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
^ It is curious that a similar humorous depiction of benzene had appeared in 1886 in the Berichte der Durstigen Chemischen Gesellschaft (Journal of the Thirsty Chemical Society), a parody of the Berichte der Deutschen Chemischen Gesellschaft , only the parody had monkeys seizing each other in a circle, rather than snakes as in Kekulé's anecdote.- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
^ 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.- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
[8] .^ 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.- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
[2] .^ Others have speculated that Kekulé's story in 1890 was a re-parody of the monkey spoof, and was a mere invention rather than a recollection of an event in his life.- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
^ It is curious that a similar humorous depiction of benzene had appeared in 1886 in the Berichte der Durstigen Chemischen Gesellschaft (Journal of the Thirsty Chemical Society), a parody of the Berichte der Deutschen Chemischen Gesellschaft , only the parody had monkeys seizing each other in a circle, rather than snakes as in Kekulé's anecdote.- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
.^ Kekulé's 1890 speech [8] in which these anecdotes appeared has been translated into English.- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
^ Translated into English by D. Wilcox and F. Greenbaum, Journal of Chemical Education , 42 (1965), 266–67.- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
[10] If one takes the anecdote as the memory of a real event, circumstances mentioned in the story suggest that it must have happened early in 1862.
[11]
Structure
Main article:
AromaticityBenzene represents a special problem in that, to account for all the bonds, there must be alternating
double carbon bonds:
[14]
The Various representaions of benzene
.^ Using X-ray diffraction, researchers discovered that all of the carbon-carbon bonds in benzene are of the same length of 140 picometres (pm).- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
^ To reflect the delocalised nature of the bonding, benzene is often depicted with a circle inside a hexagonal arrangement of carbon atoms: .- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
^ In laboratory research, toluene is now often used as a substitute for benzene.- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
.^ The C–C bond lengths are greater than a double bond (135pm) but shorter than a single bond (147pm).- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
.^ This intermediate distance is explained by electron delocalization : the electrons for C–C bonding are distributed equally between each of the six carbon atoms.- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
^ In 1865 the German chemist Friedrich August Kekulé published a paper in French (for he was then teaching in Francophone Belgium) suggesting that the structure contained a six-membered ring of carbon atoms with alternating single and double bonds.- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
^ To reflect the delocalised nature of the bonding, benzene is often depicted with a circle inside a hexagonal arrangement of carbon atoms: .- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
.^ One representation is that the structure exists as a superposition of so-called resonance structures , rather than either form individually.- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
^ Where multiple streams are combined to form a feedstock, the benzene in one of the feeds may be much higher than 25 wt.- Isomerization of Benzene-Containing Feedstocks - Patent application 10 February 2010 12:012 UTC www.faqs.org [Source type: Reference]
^ Most of the reactions thus far reported for C 60 involve addition to, rather than substitution of, the core structure.- Chemical Reactivity 10 February 2010 12:012 UTC www.cem.msu.edu [Source type: Reference]
.^ This delocalisation of electrons is known as aromaticity , and gives benzene great stability.- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
^ As expected, the resulting 10 π-electron annulene derivatives exhibit aromatic stability and reactivity as well as characteristic ring current anisotropy in the nmr.- Chemical Reactivity 10 February 2010 12:012 UTC www.cem.msu.edu [Source type: Reference]
^ The enhanced stability, often referred to as aromatic stabilization , ranges (in the above cases) from a low of 16 kcal/mol for furan to 36 kcal/mol for benzene.- Chemical Reactivity 10 February 2010 12:012 UTC www.cem.msu.edu [Source type: Reference]
.^ This enhanced stability is the fundamental property of aromatic molecules that differentiates them from molecules that are non-aromatic.- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
^ The enhanced stability, often referred to as aromatic stabilization , ranges (in the above cases) from a low of 16 kcal/mol for furan to 36 kcal/mol for benzene.- Chemical Reactivity 10 February 2010 12:012 UTC www.cem.msu.edu [Source type: Reference]
^ In cases such as these, the electron delocalization described by resonance enhances the stability of the molecules, and compounds composed of such molecules often show exceptional stability and related properties.- Chemical Reactivity 10 February 2010 12:012 UTC www.cem.msu.edu [Source type: Reference]
To reflect the delocalised nature of the bonding, benzene is often depicted with a circle inside a hexagonal arrangement of carbon atoms:
.^ As is common in organic chemistry, the carbon atoms in the diagram above have been left unlabeled.- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
.^ To reflect the delocalised nature of the bonding, benzene is often depicted with a circle inside a hexagonal arrangement of carbon atoms: .- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
^ The second tactic requires that the benzene ring be activated (made more nucleophilic) by substitution with an electron donating group such as OH or NH 2 .- Chemical Reactivity 10 February 2010 12:012 UTC www.cem.msu.edu [Source type: Reference]
^ If we extend the structure of corannulene by adding similar cycles of five benzene rings, the curvature of the resulting molecule should increase, and eventually close into a sphere of carbon atoms.- Chemical Reactivity 10 February 2010 12:012 UTC www.cem.msu.edu [Source type: Reference]
It is the side-on overlap of p-orbitals that produces the pi clouds.
.^ Benzene occurs sufficiently often as a component of organic molecules that there is a Unicode symbol with the code 232C to represent it: .- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
^ To reflect the delocalised nature of the bonding, benzene is often depicted with a circle inside a hexagonal arrangement of carbon atoms: .- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
^ (PCBs) are a class of organic compounds with 1 to 10 chlorine atoms attached to biphenyl, which is a molecule composed of two benzene rings.- Benzene Exposure Benzene Lawyer Lawsuit Benzene Cancer Attorney Leukemia Law Firm 10 February 2010 12:012 UTC www.thepicenter.com [Source type: General]
[16]
Substituted benzene derivatives
.^ Main article: Aromatic hydrocarbons Many important chemicals are derived from benzene, wherein with one or more of the hydrogen atoms is replaced with another functional group .- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
^ Hydrogenation (Reduction): Benzene and derivatives convert to cyclohexane and derivatives when treated with hydrogen at 450 K and 10 atm of pressure with a finely divided nickel catalyst .- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
^ The chemical releases contained benzene , aluminum silica, and many more harmful chemicals.
.^ Examples of simple benzene derivatives are phenol , toluene , and aniline , abbreviated PhOH, PhMe, and PhNH 2 , respectively.- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
^ Hudak A & Ungvary G (1978) Embryotoxic effects of benzene and its methyl derivatives: toluene, xylene.- Benzene (PIM 063) 10 February 2010 12:012 UTC www.inchem.org [Source type: Academic]
^ Benzene and 1,3,5,7-cyclooctatetraene are examples of annulenes; they are named [6]annulene and [8]annulene respectively, according to a general nomenclature system in which the number of pi-electrons in an annulene is designated by a number in brackets.- Chemical Reactivity 10 February 2010 12:012 UTC www.cem.msu.edu [Source type: Reference]
.^ (PCBs) are a class of organic compounds with 1 to 10 chlorine atoms attached to biphenyl, which is a molecule composed of two benzene rings.- Benzene Exposure Benzene Lawyer Lawsuit Benzene Cancer Attorney Leukemia Law Firm 10 February 2010 12:012 UTC www.thepicenter.com [Source type: General]
^ Linking benzene rings gives biphenyl , C 6 H 5 –C 6 H 5 .- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
^ Benzene rings may be joined together (fused) to give larger polycyclic aromatic compounds.- Chemical Reactivity 10 February 2010 12:012 UTC www.cem.msu.edu [Source type: Reference]
.^ Further loss of hydrogen gives "fused" aromatic hydrocarbons, such as naphthalene and anthracene .- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
^ 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.- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
^ The first example is azulene, a blue-colored 10 π-electron aromatic hydrocarbon isomeric with naphthalene.- Chemical Reactivity 10 February 2010 12:012 UTC www.cem.msu.edu [Source type: Reference]
.^ The limit of the fusion process is the hydrogen-free material graphite .- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
.^ In heterocycles , carbon atoms in the benzene ring are replaced with other elements.- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
^ To reflect the delocalised nature of the bonding, benzene is often depicted with a circle inside a hexagonal arrangement of carbon atoms: .- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
^ Main article: Aromatic hydrocarbons Many important chemicals are derived from benzene, wherein with one or more of the hydrogen atoms is replaced with another functional group .- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
.^ The most important derivatives are the rings containing nitrogen .- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
.^ Replacing one CH with N gives the compound pyridine , C 5 H 5 N. Although benzene and pyridine are structurally related, benzene cannot be converted into pyridine.- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
^ The suit alleges that the defendants released benzene into the air, although they were fully aware of the dangers.
^ Therefore in the analysis of risk or causation one must take into account the knowledge that industrial solvents cannot be produced without contamination with benzene, and therefore they contain benzene.
.^ Replacement of a second CH bond with N gives, depending on the location of the second N, pyridazine , pyrimidine , and pyrazine.- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
^ Replacing one CH with N gives the compound pyridine , C 5 H 5 N. Although benzene and pyridine are structurally related, benzene cannot be converted into pyridine.- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
Production
.^ The resulting low benzene content streams may be used as gasoline or gasoline blend stocks to result in gasolines meeting the increasingly stringent requirements for benzene imposed by various governments.- PROCESS FOR BENZENE REMOVAL FROM GASOLINE - Patent application 10 February 2010 12:012 UTC www.faqs.org [Source type: Reference]
^ Reducing the amount of material passing through the sulfur guard bed may result in a smaller guard bed being required thus reducing costs.- Isomerization of Benzene-Containing Feedstocks - Patent application 10 February 2010 12:012 UTC www.faqs.org [Source type: Reference]
- Isomerization of Benzene-Containing Feedstocks - Patent application 10 February 2010 12:012 UTC www.faqs.org [Source type: Reference]
^ This is a result of the first alkylation producing a benzene alkylate and an alcohol, where the alcohol may additionally react with benzene to form a second benzene alkylate and water.- PROCESS FOR BENZENE REMOVAL FROM GASOLINE - Patent application 10 February 2010 12:012 UTC www.faqs.org [Source type: Reference]
.^ It is produced in volcanoes and forest fires, and is also a component of cigarette smoke.- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
^ Natural sources of benzene include volcanoes and forest fires.
.^ Benzene is an aromatic hydrocarbon that is produced by the burning of natural products.
^ Up until World War II, most benzene was produced as a byproduct of coke production (or "coke-oven light oil") in the steel industry.- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
^ The product separator operates as a simple flash separator that produces a vapor stream rich in hydrogen with the remainder of its volume principally comprising C 1 and C 2 hydrocarbons.- Isomerization of Benzene-Containing Feedstocks - Patent application 10 February 2010 12:012 UTC www.faqs.org [Source type: Reference]
- Isomerization of Benzene-Containing Feedstocks - Patent application 10 February 2010 12:012 UTC www.faqs.org [Source type: Reference]
.^ During 1967, there was about 800 million gallons of benzene produced in the U.S., and by 1969, the amount of benzene increased to 1,185 million gallons with approximately 16% of the productions derived from coal.
^ At present, such uses are minimal; most benzene is consumed in the chemical industry as a raw material for numerous organic chemicals and in plastics manufacture.- Notice of Intended Changes - Benzene 10 February 2010 12:012 UTC tobaccodocuments.org [Source type: Academic]
^ Workers in the following industries may be at risk for chronic benzene poisoning: railroad, automobile, coke oven factories, print shops, and any industrial operations that involve the production of household products, gas, plastic, rubber, dyes, detergents, glue, pesticides, and some drugs.
.^ However, in the 1950s, increased demand for benzene, especially from the growing plastics industry, necessitated the production of benzene from petroleum.- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
^ At present, such uses are minimal; most benzene is consumed in the chemical industry as a raw material for numerous organic chemicals and in plastics manufacture.- Notice of Intended Changes - Benzene 10 February 2010 12:012 UTC tobaccodocuments.org [Source type: Academic]
^ Up until World War II, most benzene was produced as a byproduct of coke production (or "coke-oven light oil") in the steel industry.- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
.^ Today, most benzene comes from the petrochemical industry, with only a small fraction being produced from coal.- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
^ At present, such uses are minimal; most benzene is consumed in the chemical industry as a raw material for numerous organic chemicals and in plastics manufacture.- Notice of Intended Changes - Benzene 10 February 2010 12:012 UTC tobaccodocuments.org [Source type: Academic]
^ Up until World War II, most benzene was produced as a byproduct of coke production (or "coke-oven light oil") in the steel industry.- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
.^ At present, such uses are minimal; most benzene is consumed in the chemical industry as a raw material for numerous organic chemicals and in plastics manufacture.- Notice of Intended Changes - Benzene 10 February 2010 12:012 UTC tobaccodocuments.org [Source type: Academic]
^ Here, the liquid and vapor enthalpies can be approximated by two parallel lines (i.e., the molar latent heats of chemically similar compounds, benzene and toluene, are almost the same).- Enthalpy-Concentration Plot for a Benzene-Toluene Binary Mixture - Wolfram Demonstrations Project 10 February 2010 12:012 UTC demonstrations.wolfram.com [Source type: FILTERED WITH BAYES]
^ Populations highly exposed to benzene are as follows: 1) workers engaged in its production, 2) workers engaged in chemical industries utilizing benzene, 3) workers in industries producing materials containing benzene, 4) workers utilizing or handling compounds containing benzene, 5) people living near factories producing or utilizing benzene, and 6) exposure to engine emissions and cigarette smoking.
.^ Benzene is produced commercially through catalytic reforming of light naphtha, dealkylation of toluene, and as a coking by-product in steel mills (Weaver et al., 1983).- Benzene (PIM 063) 10 February 2010 12:012 UTC www.inchem.org [Source type: Academic]
.^ Depending on the feedstock used to produce the olefins, steam cracking can produce a benzene-rich liquid byproduct called pyrolysis gasoline .- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
^ Benzene is produced commercially through catalytic reforming of light naphtha, dealkylation of toluene, and as a coking by-product in steel mills (Weaver et al., 1983).- Benzene (PIM 063) 10 February 2010 12:012 UTC www.inchem.org [Source type: Academic]
^ Three chemical processes contribute equally to industrial benzene production: catalytic reforming , toluene hydrodealkylation, and steam cracking.- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
Catalytic reforming
.^ For example, when the feed mixture is primarily C 5 and C 6 alkanes, temperatures in the range of 60° to 160° C. are desired from a normal-isoalkane equilibrium standpoint but, in order to achieve significant opening of C 5 and C 6 cyclic hydrocarbon ring, the preferred temperature range for this invention lies between 100° to 200° C. When it is desired to also isomerize significant amounts of C 4 hydrocarbons, higher reaction temperatures are required to maintain catalyst activity.- Isomerization of Benzene-Containing Feedstocks - Patent application 10 February 2010 12:012 UTC www.faqs.org [Source type: Reference]
^ For example, when the feed mixture is primarily C 5 and C 6 alkanes, temperatures in the range of 600 to 160° C. are desired from a normal-isoalkane equilibrium standpoint but, in order to achieve significant opening of C 5 and C 6 cyclic hydrocarbon ring, the preferred temperature range for this invention lies between 1000 to 200° C. When it is desired to also isomerize significant amounts of C 4 hydrocarbons, higher reaction temperatures are required to maintain catalyst activity.- Isomerization of Benzene-Containing Feedstocks - Patent application 10 February 2010 12:012 UTC www.faqs.org [Source type: Reference]
^ Such catalysts have been found to provide satisfactory benzene saturation at conditions including temperatures as low as 38° C. (100° F.), pressures from 1400 to 4800 kPa(g) (200 to 700 psig), an inlet hydrogen to hydrocarbon ratio in the range of 0.1 to 2, and a 1 to 40 liquid hourly space velocity (LHSV).- Isomerization of Benzene-Containing Feedstocks - Patent application 10 February 2010 12:012 UTC www.faqs.org [Source type: Reference]
- Isomerization of Benzene-Containing Feedstocks - Patent application 10 February 2010 12:012 UTC www.faqs.org [Source type: Reference]
.^ Under these conditions, aliphatic hydrocarbons form rings and lose hydrogen to become aromatic hydrocarbons.- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
^ Further loss of hydrogen gives "fused" aromatic hydrocarbons, such as naphthalene and anthracene .- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
^ Von Oetingen WF (1940) II. Toxicity and potential dangers of aliphatic and aromatic hydrocarbons.- Benzene (PIM 063) 10 February 2010 12:012 UTC www.inchem.org [Source type: Academic]
.^ 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.- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
^ The reaction involves the acylation of benzene (or many other aromatic rings) with an acyl chloride using a strong Lewis acid catalyst such as aluminium chloride or iron chloride which act as a halogen carrier.- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
^ The process of claim 1, further comprising feeding hydrogen to the catalytic distillation column below the at least one reaction zone.- PROCESS FOR BENZENE REMOVAL FROM GASOLINE - Patent application 10 February 2010 12:012 UTC www.faqs.org [Source type: Reference]
The extraction step of aromatics from the reformate is designed to produce aromatics with lowest non-aromatic components.
.^ This is often called "on-purpose" methodology to produce benzene, compared to conventional BTX (benzene-toluene-xylene) processes.- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
^ So-called "BTX (Benzene-Toluene-Xylenes)" process consists of such extraction and distillation steps.- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
^ UV Fourier transform absorption cross sections of benzene, toluene, meta-, ortho, and para-xylene; m-xylene .- science-softCon UV/Vis Spectra Data Base 10 February 2010 12:012 UTC www.science-softcon.de [Source type: Academic]
.^ Its most widely-produced derivatives include styrene , which is used to make polymers and plastics, phenol for resins and adhesives (via cumene ), and cyclohexane , which is used in the manufacture of Nylon.- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
^ This is often called "on-purpose" methodology to produce benzene, compared to conventional BTX (benzene-toluene-xylene) processes.- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
^ Catalytic reforming and catalytic isomerization are two widely used processes for this upgrading.- Isomerization of Benzene-Containing Feedstocks - Patent application 10 February 2010 12:012 UTC www.faqs.org [Source type: Reference]
- Isomerization of Benzene-Containing Feedstocks - Patent application 10 February 2010 12:012 UTC www.faqs.org [Source type: Reference]
.^ Benzene is produced commercially through catalytic reforming of light naphtha, dealkylation of toluene, and as a coking by-product in steel mills (Weaver et al., 1983).- Benzene (PIM 063) 10 February 2010 12:012 UTC www.inchem.org [Source type: Academic]
^ Octane improvement can also be obtained by catalytically isomerizing the paraffinic hydrocarbons to rearrange the structure of the paraffinic hydrocarbons into branch-chained paraffins or reforming to convert the C 6 and heavier hydrocarbons to aromatic compounds.- Isomerization of Benzene-Containing Feedstocks - Patent application 10 February 2010 12:012 UTC www.faqs.org [Source type: Reference]
- Isomerization of Benzene-Containing Feedstocks - Patent application 10 February 2010 12:012 UTC www.faqs.org [Source type: Reference]
Toluene hydrodealkylation
.^ Toluene hydrodealkylation converts toluene to benzene.- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
^ Three chemical processes contribute equally to industrial benzene production: catalytic reforming , toluene hydrodealkylation, and steam cracking.- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
^ 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.- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
.^ 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.- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
^ 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.- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
^ Hydrogenation (Reduction): Benzene and derivatives convert to cyclohexane and derivatives when treated with hydrogen at 450 K and 10 atm of pressure with a finely divided nickel catalyst .- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
.^ For example, pressures, temperatures, and other operating conditions may be adjusted to achieve the desired C.sub.6/C.sub.7 split to avoid contact of the C.sub.7 compounds with the alkylation catalyst.- PROCESS FOR BENZENE REMOVAL FROM GASOLINE - Patent application 10 February 2010 12:012 UTC www.faqs.org [Source type: Reference]
^ In April 1996, Westinghouse Savannah River Company duplicated the decomposition reaction in the laboratory using simulated waste and accelerated conditions (higher temperature and greater concentrations of metals that appear to catalyze the reaction).- DNFSB/TECH-14 10 February 2010 12:012 UTC www.dnfsb.gov [Source type: Academic]
^ For example, hydrogen may be advantageously used to prolong the service life of the alkylation catalyst contained in reaction zone 12.- PROCESS FOR BENZENE REMOVAL FROM GASOLINE - Patent application 10 February 2010 12:012 UTC www.faqs.org [Source type: Reference]
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 C6H6
H2 + C6H5–C6H5
.^ 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.- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
^ At present, such uses are minimal; most benzene is consumed in the chemical industry as a raw material for numerous organic chemicals and in plastics manufacture.- Notice of Intended Changes - Benzene 10 February 2010 12:012 UTC tobaccodocuments.org [Source type: Academic]
^ Further loss of hydrogen gives "fused" aromatic hydrocarbons, such as naphthalene and anthracene .- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
.^ A typical reaction yield exceeds 95%.- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
.^ The C.sub.7 and heavier components, including toluene, may be distilled downward, avoiding or minimizing contact of C.sub.7+ aromatic compounds with the alkylation catalyst.- PROCESS FOR BENZENE REMOVAL FROM GASOLINE - Patent application 10 February 2010 12:012 UTC www.faqs.org [Source type: Reference]
^ The aromatic heterocycle pyridine is similar to benzene, and is often used as a weak base for scavanging protons.- Chemical Reactivity 10 February 2010 12:012 UTC www.cem.msu.edu [Source type: Reference]
^ Benzene in high concentrations has narcotic effects similar to toluene and other aromatics.- Sampling and Analytical Methods: Benzene, 1005 10 February 2010 12:012 UTC www.osha.gov [Source type: Academic]
.^ This is often called "on-purpose" methodology to produce benzene, compared to conventional BTX (benzene-toluene-xylene) processes.- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
^ So-called "BTX (Benzene-Toluene-Xylenes)" process consists of such extraction and distillation steps.- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
^ In laboratory research, toluene is now often used as a substitute for benzene.- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
Toluene disproportionation
.^ 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.- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
^ Toluene hydrodealkylation converts toluene to benzene.- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
^ UV Fourier transform absorption cross sections of benzene, toluene, meta-, ortho, and para-xylene; m-xylene .- science-softCon UV/Vis Spectra Data Base 10 February 2010 12:012 UTC www.science-softcon.de [Source type: Academic]
.^ Broadly speaking 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.- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
^ As its toxicity became obvious, benzene was supplanted by other solvents, especially toluene (methyl benzene), which has similar physical properties but is not as carcinogenic.- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
^ Lange A, Smolik R, Zatonski W, Szymanska (1973) Serum immunoglobulin levels in workers exposed to benzene, toluene, and xylene.- Benzene (PIM 063) 10 February 2010 12:012 UTC www.inchem.org [Source type: Academic]
.^ Combination processes using isomerization and reforming to convert naphtha range feedstocks are well known.- Isomerization of Benzene-Containing Feedstocks - Patent application 10 February 2010 12:012 UTC www.faqs.org [Source type: Reference]
- Isomerization of Benzene-Containing Feedstocks - Patent application 10 February 2010 12:012 UTC www.faqs.org [Source type: Reference]
^ The aforementioned separations may be further complicated by azeotropes that may form between water, ethers, and alcohols used in the alkylation process, as well as those that may form between hydrocarbons and water, alcohols, and ethers.- PROCESS FOR BENZENE REMOVAL FROM GASOLINE - Patent application 10 February 2010 12:012 UTC www.faqs.org [Source type: Reference]
^ Other catalysts useful in embodiments disclosed herein may include phosphorous-modified zeolites, aluminas, and silicas.- PROCESS FOR BENZENE REMOVAL FROM GASOLINE - Patent application 10 February 2010 12:012 UTC www.faqs.org [Source type: Reference]
In this process, the xylene stream exiting the TDP unit is approximately 90% paraxylene.
.^ In a study of 35 painters exposed to 3 to 49 ppm of benzene and higher concentrations of toluene and xylene, increased serum IgM, and decreased serum IgG and IgA were found (Lange et al., 1973).- Benzene (PIM 063) 10 February 2010 12:012 UTC www.inchem.org [Source type: Academic]
^ Additionally, toluene, xylenes, and ethylbenzene each have a higher octane rating than benzene.- PROCESS FOR BENZENE REMOVAL FROM GASOLINE - Patent application 10 February 2010 12:012 UTC www.faqs.org [Source type: Reference]
^ Locally, benzene can produce erythema, a burning sensation, and in more severe cases, edema and even blistering.- ATSDR - MMG: Benzene 10 February 2010 12:012 UTC www.atsdr.cdc.gov [Source type: Academic]
Steam cracking
.^ The process of claim 1 wherein the hydrogen-rich gas stream is mixed with said feedstock to produce a hydrogen to hydrocarbon ratio in the range of 0.- Isomerization of Benzene-Containing Feedstocks - Patent application 10 February 2010 12:012 UTC www.faqs.org [Source type: Reference]
^ Benzene may be present in gasoline and other petroleum products up to 1%, as a natural part of the cracking process.- Sampling and Analytical Methods: Benzene, 1005 10 February 2010 12:012 UTC www.osha.gov [Source type: Academic]
^ In the reforming processing, C 6 cycloparaffins and other higher boiling cyclic hydrocarbons are converted to benzene and benzene derivatives.- Isomerization of Benzene-Containing Feedstocks - Patent application 10 February 2010 12:012 UTC www.faqs.org [Source type: Reference]
.^ Depending on the feedstock used to produce the olefins, steam cracking can produce a benzene-rich liquid byproduct called pyrolysis gasoline .- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
^ Up until World War II, most benzene was produced as a byproduct of coke production (or "coke-oven light oil") in the steel industry.- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
^ The feedstocks that are used in this invention will typically include hydrocarbon fractions rich in C 4 -C 6 normal paraffins.- Isomerization of Benzene-Containing Feedstocks - Patent application 10 February 2010 12:012 UTC www.faqs.org [Source type: Reference]
- Isomerization of Benzene-Containing Feedstocks - Patent application 10 February 2010 12:012 UTC www.faqs.org [Source type: Reference]
.^ Pyrolysis gasoline can be blended with other hydrocarbons as a gasoline additive, or distilled (in BTX process) to separate it into its components, including benzene.- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
^ The separator may contain packing or other liquid vapor separation devices to limit the carryover of hydrocarbons.- Isomerization of Benzene-Containing Feedstocks - Patent application 10 February 2010 12:012 UTC www.faqs.org [Source type: Reference]
- Isomerization of Benzene-Containing Feedstocks - Patent application 10 February 2010 12:012 UTC www.faqs.org [Source type: Reference]
^ Depending on the feedstock used to produce the olefins, steam cracking can produce a benzene-rich liquid byproduct called pyrolysis gasoline .- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
Uses
Early uses
.^ In the 19th and early-20th centuries, benzene was used as an after-shave lotion because of its pleasant smell.- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
.^ Prior to the 1920s, benzene was frequently used as an industrial solvent, especially for degreasing metal.- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
^ At present, such uses are minimal; most benzene is consumed in the chemical industry as a raw material for numerous organic chemicals and in plastics manufacture.- Notice of Intended Changes - Benzene 10 February 2010 12:012 UTC tobaccodocuments.org [Source type: Academic]
^ An increased frequency of chromatid and isochromatid breaks was found in children of women exposed during pregnancy to a mix of benzene and other solvents in the printing industry and chemical laboratories (Funes-Cravioto et al., 1977).- Benzene (PIM 063) 10 February 2010 12:012 UTC www.inchem.org [Source type: Academic]
.^ Physical properties of: Benzene .- Benzene | Marketizer.com 10 February 2010 12:012 UTC pr76.marketizer.com [Source type: General]
^ Technical Information Physical properties of: Benzene Safety and handling information for: Benzene .- Benzene | Marketizer.com 10 February 2010 12:012 UTC pr76.marketizer.com [Source type: General]
^ Ikeda M & Ohtsuji H (1971) Phenobarbital-induced protection against toxicity of toluene and benzene in the rat.- Benzene (PIM 063) 10 February 2010 12:012 UTC www.inchem.org [Source type: Academic]
.^ In 1903, Ludwig Roselius popularized the use of benzene to decaffeinate coffee.- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
.^ This discovery led to the production of Sanka (the letters "ka" in the brand name stand for kaffein ).- Benzene: Encyclopedia of chemistry, analytics & pharmaceutics with 64,557 entries. 10 February 2010 12:012 UTC www.chemie.de [Source type: Academic]
This process was later discontinued.
.^ At present, such uses are minimal; most benzene is consumed in the chemical industry as a raw material for numerous organic chemicals and in plastics manufacture.- Notice of Intended Changes - Benzene 10 February 2010 12:012 UTC tobaccodocuments.org [Source type: Academic]
^ While incidental exposure to Benzene from surrounding air is not usually harmful, prolonged exposure around gas stations or other areas where products made with Benzene are used can cause many symptoms such as dizziness, headaches, confusion, tremors, rapid heart rate, and unconsciousness.- Benzene Exposure Benzene Lawyer Lawsuit Benzene Cancer Attorney Leukemia Law Firm 10 February 2010 12:012 UTC www.thepicenter.com [Source type: General]
^ While it is found naturally in the environment and in airborne compounds such as cigarette smoke and gasoline, the biggest threat is from the production of manmade products created with it.- Benzene Exposure Benzene Lawyer Lawsuit Benzene Cancer Attorney Leukemia Law Firm 10 February 2010 12:012 UTC www.thepicenter.com [Source type: General]
.^ In some countries, benzene continues to be used as a household cleaner.- Benzene (PIM 063) 10 February 2010 12:012 UTC www.inchem.org [Source type: Academic]
^ Where can more information about benzene be found?- ATSDR - MMG: Benzene 10 February 2010 12:012 UTC www.atsdr.cdc.gov [Source type: Academic]
^ At present, such uses are minimal; most benzene is consumed in the chemical industry as a raw material for numerous organic chemicals and in plastics manufacture.- Notice of Intended Changes - Benzene 10 February 2010 12:012 UTC tobaccodocuments.org [Source type: Academic]
.^ At present, such uses are minimal; most benzene is consumed in the chemical industry as a raw material for numerous organic chemicals and in plastics manufacture.- Notice of Intended Changes - Benzene 10 February 2010 12:012 UTC tobaccodocuments.org [Source type: Academic]
^ While incidental exposure to Benzene from surrounding air is not usually harmful, prolonged exposure around gas stations or other areas where products made with Benzene are used can cause many symptoms such as dizziness, headaches, confusion, tremors, rapid heart rate, and unconsciousness.- Benzene Exposure Benzene Lawyer Lawsuit Benzene Cancer Attorney Leukemia Law Firm 10 February 2010 12:012 UTC www.thepicenter.com [Source type: General]
^ Benzene is used mainly as a raw material for synthesizing chemicals such as styrene, phenol, and cyclohexane and for manufacturing dyes, detergents, explosives, rubber, plastics, and pharmaceuticals.- ATSDR - MMG: Benzene 10 February 2010 12:012 UTC www.atsdr.cdc.gov [Source type: Academic]
.^ There is no specific antidote for benzene, but its effects can be treated, and most exposed persons recover fully.- ATSDR - MMG: Benzene 10 February 2010 12:012 UTC www.atsdr.cdc.gov [Source type: Academic]
^ The OSHA benzene standard mandates that urinary phenol-testing be performed on all workers exposed to benzene in an emergency situation (see Follow-up below).- ATSDR - MMG: Benzene 10 February 2010 12:012 UTC www.atsdr.cdc.gov [Source type: Academic]
^ Victims exposed only to benzene vapor who have no skin or eye irritation do not need decontamination.- ATSDR - MMG: Benzene 10 February 2010 12:012 UTC www.atsdr.cdc.gov [Source type: Academic]
This very dangerous practice has been almost totally eliminated.
.^ Therefore, processes are needed for reducing the benzene content of the gasoline pool while maintaining sufficient conversion to satisfy the octane requirements of modern engines.- Isomerization of Benzene-Containing Feedstocks - Patent application 10 February 2010 12:012 UTC www.faqs.org [Source type: Reference]
- Isomerization of Benzene-Containing Feedstocks - Patent application 10 February 2010 12:012 UTC www.faqs.org [Source type: Reference]
^ Those tests showed the benzene release rate was a function of slurry pump operation (i.e., pump operation increased the benzene release rate).- DNFSB/TECH-14 10 February 2010 12:012 UTC www.dnfsb.gov [Source type: Academic]
^ Benzene has a high octane number value and has been previously blended into gasoline.- Isomerization of Benzene-Containing Feedstocks - Patent application 10 February 2010 12:012 UTC www.faqs.org [Source type: Reference]
- Isomerization of Benzene-Containing Feedstocks - Patent application 10 February 2010 12:012 UTC www.faqs.org [Source type: Reference]
.^ At present, such uses are minimal; most benzene is consumed in the chemical industry as a raw material for numerous organic chemicals and in plastics manufacture.- Notice of Intended Changes - Benzene 10 February 2010 12:012 UTC tobaccodocuments.org [Source type: Academic]
^ In the United States benzene averages less than 2% by volume in gasoline, and in Europe the concentration is often 4 to 5% by volume and may exceed these concentrations with certain blends.- Benzene (PIM 063) 10 February 2010 12:012 UTC www.inchem.org [Source type: Academic]
^ The feed stream is heated by heat exchange with the effluent of the benzene saturation reactor using a heat exchanger before being passed to the sulfur guard bed.- Isomerization of Benzene-Containing Feedstocks - Patent application 10 February 2010 12:012 UTC www.faqs.org [Source type: Reference]
- Isomerization of Benzene-Containing Feedstocks - Patent application 10 February 2010 12:012 UTC www.faqs.org [Source type: Reference]
.^ In some instances, it is probable that both the exposure to benzene on an industrial basis and exposure to other toxic chemical (such as cigarette smoking) on a nonindustrial basis are additive to causation.
.^ Try to avoid administering epinephrine due to the possible myocardial sensitizing effect of benzene.- ATSDR - MMG: Benzene 10 February 2010 12:012 UTC www.atsdr.cdc.gov [Source type: Academic]
^ In the United States, smoking accounts for approximately half of the total population exposure to benzene (Wallace, 1989).- Benzene (PIM 063) 10 February 2010 12:012 UTC www.inchem.org [Source type: Academic]
^ Industrial Production and Usage Benzene is produced in large quantities in the United States.
[17] .^ This invention relates more specifically to the processing of benzene-containing hydrocarbon feeds and the isomerization of light paraffins.- Isomerization of Benzene-Containing Feedstocks - Patent application 10 February 2010 12:012 UTC www.faqs.org [Source type: Reference]
^ The benzene content in a gasoline pool is reduced by a process that hydrogenates a benzene-containing isomerization zone feedstream.- Isomerization of Benzene-Containing Feedstocks - Patent application 10 February 2010 12:012 UTC www.faqs.org [Source type: Reference]
The
United States Environmental Protection Agency has new regulations that will lower the benzene content in gasoline to 0.62% in 2011.
[18]
Current uses
.^ At present, such uses are minimal; most benzene is consumed in the chemical industry as a raw material for numerous organic chemicals and in plastics manufacture.- Notice of Intended Changes - Benzene 10 February 2010 12:012 UTC tobaccodocuments.org [Source type: Academic]
^ USES 4.1 Uses 4.1.1 Uses 4.1.2 Description Benzene is used as an intermediate in the manufacture of a number of chemicals, including ethylbenzene (used in the synthesis of styrene), cumene (used in the synthesis of phenol and for the manufacture of phenolic resins and nylon intermediates), cyclohexane (used to make nylon resins), and nitrobenzene (used in the synthesis of aniline).- Benzene (PIM 063) 10 February 2010 12:012 UTC www.inchem.org [Source type: Academic]
^ Benzene is used mainly as a raw material for synthesizing chemicals such as styrene, phenol, and cyclohexane and for manufacturing dyes, detergents, explosives, rubber, plastics, and pharmaceuticals.- ATSDR - MMG: Benzene 10 February 2010 12:012 UTC www.atsdr.cdc.gov [Source type: Academic]
.^ USES 4.1 Uses 4.1.1 Uses 4.1.2 Description Benzene is used as an intermediate in the manufacture of a number of chemicals, including ethylbenzene (used in the synthesis of styrene), cumene (used in the synthesis of phenol and for the manufacture of phenolic resins and nylon intermediates), cyclohexane (used to make nylon resins), and nitrobenzene (used in the synthesis of aniline).- Benzene (PIM 063) 10 February 2010 12:012 UTC www.inchem.org [Source type: Academic]
^ At present, such uses are minimal; most benzene is consumed in the chemical industry as a raw material for numerous organic chemicals and in plastics manufacture.- Notice of Intended Changes - Benzene 10 February 2010 12:012 UTC tobaccodocuments.org [Source type: Academic]
^ Benzene is used mainly as a raw material for synthesizing chemicals such as styrene, phenol, and cyclohexane and for manufacturing dyes, detergents, explosives, rubber, plastics, and pharmaceuticals.- ATSDR - MMG: Benzene 10 February 2010 12:012 UTC www.atsdr.cdc.gov [Source type: Academic]
.^ Plastics, synthetic rubber, dyes, paints, varnishes, resins, detergent raw materials and pesticides are all produced on the basis of benzene.- Benzene 10 February 2010 12:012 UTC www2.gtz.de [Source type: Academic]
^ Stockton RecordExtraction uses a method called hydraulic fracturing in which huge amounts of water laced with benzene and proprietary chemicals are forced into the shale ...- Benzene Exposure Benzene Lawyer Lawsuit Benzene Cancer Attorney Leukemia Law Firm 10 February 2010 12:012 UTC www.thepicenter.com [Source type: General]
^ In some countries, benzene continues to be used as a household cleaner.- Benzene (PIM 063) 10 February 2010 12:012 UTC www.inchem.org [Source type: Academic]
.^ During 1967, there was about 800 million gallons of benzene produced in the U.S., and by 1969, the amount of benzene increased to 1,185 million gallons with approximately 16% of the productions derived from coal.
^ USES 4.1 Uses 4.1.1 Uses 4.1.2 Description Benzene is used as an intermediate in the manufacture of a number of chemicals, including ethylbenzene (used in the synthesis of styrene), cumene (used in the synthesis of phenol and for the manufacture of phenolic resins and nylon intermediates), cyclohexane (used to make nylon resins), and nitrobenzene (used in the synthesis of aniline).- Benzene (PIM 063) 10 February 2010 12:012 UTC www.inchem.org [Source type: Academic]
^ Benzene is used mainly as a raw material for synthesizing chemicals such as styrene, phenol, and cyclohexane and for manufacturing dyes, detergents, explosives, rubber, plastics, and pharmaceuticals.- ATSDR - MMG: Benzene 10 February 2010 12:012 UTC www.atsdr.cdc.gov [Source type: Academic]
In laboratory research,
toluene is now often used as a substitute for benzene. The solvent-properties of the two are similar but toluene is less toxic and has a wider liquid range.
.^ This modification is essentially an adaptation of sampling probes and gas chromatograph analysis capability used in the depletion of the benzene inventory in Tank 48.- DNFSB/TECH-14 10 February 2010 12:012 UTC www.dnfsb.gov [Source type: Academic]
^ Information Required in the Analysis of Benzene Exposure and Hematological Malignancies Detailed history of exposure, including, frequency, duration and symptoms during exposure (medical records, depositions, and MSDS).
^ The use of chromosomal abnormalities as a biological marker of exposure in humans have become an important tool in the research.
Major commodity chemicals and polymers derived from benzene
Reactions
.^ Benzene's sweet aromatic odor generally provides adequate warning of hazardous concentrations for acute exposure.- ATSDR - MMG: Benzene 10 February 2010 12:012 UTC www.atsdr.cdc.gov [Source type: Academic]
Benzene is sufficiently
nucleophilic that it undergoes substitution by
acylium ions or alkyl
carbocations to give substituted derivatives.
Electrophilic aromatic substitution of benzene
-
Friedel-Crafts acylation of benzene by acetyl chloride
-
Friedel-Crafts alkylation of benzene with methyl chloride
-
- Sulfonation. The most common method involves mixing sulfuric acid with sulfate, a mixture called fuming sulfuric acid. The sulfuric acid protonates the sulfate, giving the sulfur atom a permanent, rather than resonance stabilized positive formal charge. This molecule is very electrophillic and Electrophillic Aromatic Substitution then occurs.
- Nitration: Benzene undergoes nitration with nitronium ions (NO2+) as the electrophile. Thus, warming benzene at 50-55 degrees Celsius, with a combination of concentrated sulfuric and nitric acid to produce the electrophile, gives nitrobenzene.
- Hydrogenation(Reduction): Benzene and derivatives convert to cyclohexane and derivatives when treated with hydrogen at 450 K and 10 atm of pressure with a finely divided nickel catalyst.
- 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.
Environmental transformation
.^ Sammett D, Lee EW, Kocsis JJ, Snyder R (1979) Partial hepatectomy reduces both metabolism and toxicity of benzene.- Benzene (PIM 063) 10 February 2010 12:012 UTC www.inchem.org [Source type: Academic]
^ Metabolism Benzene is both exhaled unchanged in the lungs and excreted as metabolites in the urine.- Benzene (PIM 063) 10 February 2010 12:012 UTC www.inchem.org [Source type: Academic]
^ High risk circumstances of poisoning The most common form of exposure to benzene is occupational, and both occupational and environmental exposures to benzene are overwhelmingly through inhalation.- Benzene (PIM 063) 10 February 2010 12:012 UTC www.inchem.org [Source type: Academic]
In bacteria,
dioxygenase enzyme can add an
oxygen molecule 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 to
catechol.
Health effects
A bottle of benzene. The warnings show benzene is a toxic and flammable liquid.
.^ What immediate health effects can result from benzene exposure?- ATSDR - MMG: Benzene 10 February 2010 12:012 UTC www.atsdr.cdc.gov [Source type: Academic]
^ Did you know that the toxic effects of benzene exposure can show up as late as 29 years after the first exposure?- Benzene - Attorney, Lawsuit, Law Suit, Case, Claim, Settlement, Lawyer, Litigation 10 February 2010 12:012 UTC benzene.legalview.info [Source type: General]
^ Repeated exposure to high levels of benzene (≤200 ppm) can result in persistent CNS effects.- ATSDR - MMG: Benzene 10 February 2010 12:012 UTC www.atsdr.cdc.gov [Source type: Academic]
.^ It is found in trace amounts in cigarette smoke and drinking water, as a contaminant in some industrial solvents, and as a constituent of motor fuels, unleaded gasoline in particular.- ATSDR - MMG: Benzene 10 February 2010 12:012 UTC www.atsdr.cdc.gov [Source type: Academic]
^ Environmental exposure is greatest in areas of heavy automobile use due to the presence of benzene in tailpipe emissions, near service stations, and from tobacco smoke (ATSDR, 1993).- Benzene (PIM 063) 10 February 2010 12:012 UTC www.inchem.org [Source type: Academic]
^ Populations highly exposed to benzene are as follows: 1) workers engaged in its production, 2) workers engaged in chemical industries utilizing benzene, 3) workers in industries producing materials containing benzene, 4) workers utilizing or handling compounds containing benzene, 5) people living near factories producing or utilizing benzene, and 6) exposure to engine emissions and cigarette smoking.
[19] .^ Plastics, synthetic rubber, dyes, paints, varnishes, resins, detergent raw materials and pesticides are all produced on the basis of benzene.- Benzene 10 February 2010 12:012 UTC www2.gtz.de [Source type: Academic]
^ Benzene is a chemical solvent derived from petroleum used to manufacture a wide variety of products, including inks, dyes, plastics, detergents, pesticides and gasoline.- Benzene - Attorney, Lawsuit, Law Suit, Case, Claim, Settlement, Lawyer, Litigation 10 February 2010 12:012 UTC benzene.legalview.info [Source type: General]
^ Benzene reacts explosively with strong oxidizers, such as perchlorates and nitric acid, and many fluorides.- ATSDR - MMG: Benzene 10 February 2010 12:012 UTC www.atsdr.cdc.gov [Source type: Academic]
.^ The low-level decontaminated salt solution will be fed to the Z-Area Saltstone Facility, where it will be converted to a cemented waste form for on-site disposal in permanent vaults.- DNFSB/TECH-14 10 February 2010 12:012 UTC www.dnfsb.gov [Source type: Academic]
^ Because the benzene has a higher molecular weight compared to air (78 versus 29) or water vapor (18), .- DNFSB/TECH-14 10 February 2010 12:012 UTC www.dnfsb.gov [Source type: Academic]
^ However, these concentrations may be decreased markedly in light of the intended changes in acceptable workplace benzene levels for 1993 to 1994 (ACGIH, 1993).- Benzene (PIM 063) 10 February 2010 12:012 UTC www.inchem.org [Source type: Academic]
.^ Even short-term exposure can cause headaches, dizziness, confusion and sometimes death when benzene is breathed or ingested.- Benzene - Attorney, Lawsuit, Law Suit, Case, Claim, Settlement, Lawyer, Litigation 10 February 2010 12:012 UTC benzene.legalview.info [Source type: General]
^ Breathing benzene vapor in small amounts can cause headache, dizziness, drowsiness, or nausea.- ATSDR - MMG: Benzene 10 February 2010 12:012 UTC www.atsdr.cdc.gov [Source type: Academic]
^ VERDICT Exposure to high concentration of the chemical Benzene in the workplace - temporary breathing and equilibrium problems and severe migraine headaches continuing intermittently -inability to continue work.- Benzene - Attorney, Lawsuit, Law Suit, Case, Claim, Settlement, Lawyer, Litigation 10 February 2010 12:012 UTC benzene.legalview.info [Source type: General]
.^ If swallowed, benzene can irritate the stomach, causing nausea, vomiting, and diarrhea.- ATSDR - MMG: Benzene 10 February 2010 12:012 UTC www.atsdr.cdc.gov [Source type: Academic]
^ Even short-term exposure can cause headaches, dizziness, confusion and sometimes death when benzene is breathed or ingested.- Benzene - Attorney, Lawsuit, Law Suit, Case, Claim, Settlement, Lawyer, Litigation 10 February 2010 12:012 UTC benzene.legalview.info [Source type: General]
^ Repeated exposure to high levels of benzene (≤200 ppm) can result in persistent CNS effects.- ATSDR - MMG: Benzene 10 February 2010 12:012 UTC www.atsdr.cdc.gov [Source type: Academic]
.^ Even short-term exposure can cause headaches, dizziness, confusion and sometimes death when benzene is breathed or ingested.- Benzene - Attorney, Lawsuit, Law Suit, Case, Claim, Settlement, Lawyer, Litigation 10 February 2010 12:012 UTC benzene.legalview.info [Source type: General]
^ Did you know that the toxic effects of benzene exposure can show up as late as 29 years after the first exposure?- Benzene - Attorney, Lawsuit, Law Suit, Case, Claim, Settlement, Lawyer, Litigation 10 February 2010 12:012 UTC benzene.legalview.info [Source type: General]
^ Despite its sweet smell and colorless appearance, benzene is known to cause leukemia (bone marrow cancer) with chronic exposure, as well as anemia and immune deficiency.- Benzene - Attorney, Lawsuit, Law Suit, Case, Claim, Settlement, Lawyer, Litigation 10 February 2010 12:012 UTC benzene.legalview.info [Source type: General]
.^ Benzene is a myclotoxicant known to suppress bone marrow cell proliferation and to induce hematologic disorders in humans and animals.- Sampling and Analytical Methods: Benzene, 1005 10 February 2010 12:012 UTC www.osha.gov [Source type: Academic]
^ Despite its sweet smell and colorless appearance, benzene is known to cause leukemia (bone marrow cancer) with chronic exposure, as well as anemia and immune deficiency.- Benzene - Attorney, Lawsuit, Law Suit, Case, Claim, Settlement, Lawyer, Litigation 10 February 2010 12:012 UTC benzene.legalview.info [Source type: General]
^ Baarson KA, Snyder CA, Green JD, Sellakumar A, Goldstein BD & Albert RE (1982) The hematotoxic effects of inhaled benzene on peripheral blood, bone marrow, and spleen cells are increased by ingested ethanol.- Benzene (PIM 063) 10 February 2010 12:012 UTC www.inchem.org [Source type: Academic]
.^ Benzene may cause central nervous system depression, cardiac arrhythmias, cutaneous burns and respiratory irritation.- ATSDR - MMG: Benzene 10 February 2010 12:012 UTC www.atsdr.cdc.gov [Source type: Academic]
^ Benzene may cause central nervous system depression, cardiac dysrhythmias, cutaneous burns, and respiratory irritation.- ATSDR - MMG: Benzene 10 February 2010 12:012 UTC www.atsdr.cdc.gov [Source type: Academic]
^ Benzene may cause central nervous system depression and arrhythmias to persons acutely exposed.- ATSDR - MMG: Benzene 10 February 2010 12:012 UTC www.atsdr.cdc.gov [Source type: Academic]
.^ Despite its sweet smell and colorless appearance, benzene is known to cause leukemia (bone marrow cancer) with chronic exposure, as well as anemia and immune deficiency.- Benzene - Attorney, Lawsuit, Law Suit, Case, Claim, Settlement, Lawyer, Litigation 10 February 2010 12:012 UTC benzene.legalview.info [Source type: General]
^ Haematological abnormalities, especially anemia, leukopenia, thrombocytopenia, pancytopenia, or acute myelogenous leukemia, associated with chronic use of benzene suggest benzene poisoning.- Benzene (PIM 063) 10 February 2010 12:012 UTC www.inchem.org [Source type: Academic]
^ Chronic benzene exposure is associated with an increased risk of leukemia.- Benzene (PIM 063) 10 February 2010 12:012 UTC www.inchem.org [Source type: Academic]
.^ VERDICT Exposure to high concentration of the chemical Benzene in the workplace - temporary breathing and equilibrium problems and severe migraine headaches continuing intermittently -inability to continue work.- Benzene - Attorney, Lawsuit, Law Suit, Case, Claim, Settlement, Lawyer, Litigation 10 February 2010 12:012 UTC benzene.legalview.info [Source type: General]
^ Occupational Safety and Health Administration: 29 CFR Pan 1910, Occupational Exposure to Benzene; Final Rule.- Notice of Intended Changes - Benzene 10 February 2010 12:012 UTC tobaccodocuments.org [Source type: Academic]
^ Sherwood RJ (1988) Pharmacokinetics of benzene in a human after exposure at about the occupational limit.- Benzene (PIM 063) 10 February 2010 12:012 UTC www.inchem.org [Source type: Academic]
.^ Autopsy was unremarkable except for elevated benzene levels: blood 0.38 mg%, brain 1.38 mg%, and liver 0.28 mg%.- Benzene (PIM 063) 10 February 2010 12:012 UTC www.inchem.org [Source type: Academic]
^ Pulmonary aspiration of toxic vomitus or ingested liquid benzene may cause severe hemorrhagic inflammation of the lungs.- ATSDR - MMG: Benzene 10 February 2010 12:012 UTC www.atsdr.cdc.gov [Source type: Academic]
^ In human autopsies on individuals dying shortly after exposure, high levels of benzene were found in the brain, with lower levels in the fat, blood, kidneys, and liver (Tauber, 1970; Winek & Collom, 1971).- Benzene (PIM 063) 10 February 2010 12:012 UTC www.inchem.org [Source type: Academic]
.^ Benzene exposure can cause chromosomal aberrations in animals and humans.- Sampling and Analytical Methods: Benzene, 1005 10 February 2010 12:012 UTC www.osha.gov [Source type: Academic]
^ Benzene is a myclotoxicant known to suppress bone marrow cell proliferation and to induce hematologic disorders in humans and animals.- Sampling and Analytical Methods: Benzene, 1005 10 February 2010 12:012 UTC www.osha.gov [Source type: Academic]
^ Despite its sweet smell and colorless appearance, benzene is known to cause leukemia (bone marrow cancer) with chronic exposure, as well as anemia and immune deficiency.- Benzene - Attorney, Lawsuit, Law Suit, Case, Claim, Settlement, Lawyer, Litigation 10 February 2010 12:012 UTC benzene.legalview.info [Source type: General]
.^ Benzene is a myclotoxicant known to suppress bone marrow cell proliferation and to induce hematologic disorders in humans and animals.- Sampling and Analytical Methods: Benzene, 1005 10 February 2010 12:012 UTC www.osha.gov [Source type: Academic]
^ The Erexson data(57> are the lowest concentrations of inhaled benzene that have been reported to induce genotoxicity.- Notice of Intended Changes - Benzene 10 February 2010 12:012 UTC tobaccodocuments.org [Source type: Academic]
^ Benzene is classified as a human carcinogen by American Conference of Governmental Industrial Hygienists (ACGIH) and International Agency for Research on Cancer (IARC).- Sampling and Analytical Methods: Benzene, 1005 10 February 2010 12:012 UTC www.osha.gov [Source type: Academic]
.^ In view of the fact that benzene readily ingresses into the atmosphere on account of its physical properties, it can be transported over long distances despite relatively short transformation reactions.- Benzene 10 February 2010 12:012 UTC www2.gtz.de [Source type: Academic]
.^ Benzene exposure can cause chromosomal aberrations in animals and humans.- Sampling and Analytical Methods: Benzene, 1005 10 February 2010 12:012 UTC www.osha.gov [Source type: Academic]
^ Benzene is a myclotoxicant known to suppress bone marrow cell proliferation and to induce hematologic disorders in humans and animals.- Sampling and Analytical Methods: Benzene, 1005 10 February 2010 12:012 UTC www.osha.gov [Source type: Academic]
^ Despite its sweet smell and colorless appearance, benzene is known to cause leukemia (bone marrow cancer) with chronic exposure, as well as anemia and immune deficiency.- Benzene - Attorney, Lawsuit, Law Suit, Case, Claim, Settlement, Lawyer, Litigation 10 February 2010 12:012 UTC benzene.legalview.info [Source type: General]
.^ Despite its sweet smell and colorless appearance, benzene is known to cause leukemia (bone marrow cancer) with chronic exposure, as well as anemia and immune deficiency.- Benzene - Attorney, Lawsuit, Law Suit, Case, Claim, Settlement, Lawyer, Litigation 10 February 2010 12:012 UTC benzene.legalview.info [Source type: General]
^ Animal experiments exposing pregnant mice and rats to inhaled benzene in general demonstrated increased fetal skeletal variants and reduced fetal weight, but failed to demonstrate consistent convincing evidence of teratogenecity.- Benzene (PIM 063) 10 February 2010 12:012 UTC www.inchem.org [Source type: Academic]
^ Benzene exposure can cause chromosomal aberrations in animals and humans.- Sampling and Analytical Methods: Benzene, 1005 10 February 2010 12:012 UTC www.osha.gov [Source type: Academic]
[20][21]
.^ VERDICT Exposure to high concentration of the chemical Benzene in the workplace - temporary breathing and equilibrium problems and severe migraine headaches continuing intermittently -inability to continue work.- Benzene - Attorney, Lawsuit, Law Suit, Case, Claim, Settlement, Lawyer, Litigation 10 February 2010 12:012 UTC benzene.legalview.info [Source type: General]
^ Repeated exposure to high levels of benzene (≤200 ppm) can result in persistent CNS effects.- ATSDR - MMG: Benzene 10 February 2010 12:012 UTC www.atsdr.cdc.gov [Source type: Academic]
^ OSHA mandates that acutely exposed workers who have urinary phenol levels above 75 mg/L receive periodic CBCs (at least monthly for 3 months) to monitor potential bone marrow effects.- ATSDR - MMG: Benzene 10 February 2010 12:012 UTC www.atsdr.cdc.gov [Source type: Academic]
.^ However, effects of benzene exposure in pregnant women is not well understood.- Benzene (PIM 063) 10 February 2010 12:012 UTC www.inchem.org [Source type: Academic]
^ Despite its sweet smell and colorless appearance, benzene is known to cause leukemia (bone marrow cancer) with chronic exposure, as well as anemia and immune deficiency.- Benzene - Attorney, Lawsuit, Law Suit, Case, Claim, Settlement, Lawyer, Litigation 10 February 2010 12:012 UTC benzene.legalview.info [Source type: General]
^ Chronic exposure of 1 to 25 years at benzene concentrations of 75 ppm has been associated with the development of anemia and leukopenia (Kipen et al., 1989).- Benzene (PIM 063) 10 February 2010 12:012 UTC www.inchem.org [Source type: Academic]
.^ Benzene is a myclotoxicant known to suppress bone marrow cell proliferation and to induce hematologic disorders in humans and animals.- Sampling and Analytical Methods: Benzene, 1005 10 February 2010 12:012 UTC www.osha.gov [Source type: Academic]
^ Despite its sweet smell and colorless appearance, benzene is known to cause leukemia (bone marrow cancer) with chronic exposure, as well as anemia and immune deficiency.- Benzene - Attorney, Lawsuit, Law Suit, Case, Claim, Settlement, Lawyer, Litigation 10 February 2010 12:012 UTC benzene.legalview.info [Source type: General]
^ Animal experiments exposing pregnant mice and rats to inhaled benzene in general demonstrated increased fetal skeletal variants and reduced fetal weight, but failed to demonstrate consistent convincing evidence of teratogenecity.- Benzene (PIM 063) 10 February 2010 12:012 UTC www.inchem.org [Source type: Academic]
.^ Usage: In the chemical industry pure benzene forms the most important basis for aromatic intermediate products as well as for the group of cycloaliphatic compounds.- Benzene 10 February 2010 12:012 UTC www2.gtz.de [Source type: Academic]
^ Wong O (1987) An industry wide mortality study of chemical workers occupationally exposed to benzene.- Benzene (PIM 063) 10 February 2010 12:012 UTC www.inchem.org [Source type: Academic]
^ Chronic benzene exposure has also been associated with lung cancer in epidemiological studies.- Sampling and Analytical Methods: Benzene, 1005 10 February 2010 12:012 UTC www.osha.gov [Source type: Academic]
.^ Benzene is a human and rodent clastogen and carcinogen.- Notice of Intended Changes - Benzene 10 February 2010 12:012 UTC tobaccodocuments.org [Source type: Academic]
^ The Department of Health and Human Services has determined that benzene is a known human carcinogen.- ATSDR - MMG: Benzene 10 February 2010 12:012 UTC www.atsdr.cdc.gov [Source type: Academic]
^ The rodent carcinogenicity data support the designation of benzene as a known human carcinogen.- Notice of Intended Changes - Benzene 10 February 2010 12:012 UTC tobaccodocuments.org [Source type: Academic]
.^ Repeated exposure to benzene may cause a blood disorder (i.e., aplastic anemia and pancytopenia) and cancer of blood-forming cells (i.e., leukemia).- ATSDR - MMG: Benzene 10 February 2010 12:012 UTC www.atsdr.cdc.gov [Source type: Academic]
^ Even short-term exposure can cause headaches, dizziness, confusion and sometimes death when benzene is breathed or ingested.- Benzene - Attorney, Lawsuit, Law Suit, Case, Claim, Settlement, Lawyer, Litigation 10 February 2010 12:012 UTC benzene.legalview.info [Source type: General]
^ Despite its sweet smell and colorless appearance, benzene is known to cause leukemia (bone marrow cancer) with chronic exposure, as well as anemia and immune deficiency.- Benzene - Attorney, Lawsuit, Law Suit, Case, Claim, Settlement, Lawyer, Litigation 10 February 2010 12:012 UTC benzene.legalview.info [Source type: General]
.^ Despite its sweet smell and colorless appearance, benzene is known to cause leukemia (bone marrow cancer) with chronic exposure, as well as anemia and immune deficiency.- Benzene - Attorney, Lawsuit, Law Suit, Case, Claim, Settlement, Lawyer, Litigation 10 February 2010 12:012 UTC benzene.legalview.info [Source type: General]
^ Haematological abnormalities, especially anemia, leukopenia, thrombocytopenia, pancytopenia, or acute myelogenous leukemia, associated with chronic use of benzene suggest benzene poisoning.- Benzene (PIM 063) 10 February 2010 12:012 UTC www.inchem.org [Source type: Academic]
^ Chronic benzene exposure in the workplace has been associated with hematologic disorders (i.e., thrombocytopenia, aplastic anemia, pancytopenia, and acute myelgenous leukemia).- ATSDR - MMG: Benzene 10 February 2010 12:012 UTC www.atsdr.cdc.gov [Source type: Academic]
.^ VERDICT Exposure to high concentration of the chemical Benzene in the workplace - temporary breathing and equilibrium problems and severe migraine headaches continuing intermittently -inability to continue work.- Benzene - Attorney, Lawsuit, Law Suit, Case, Claim, Settlement, Lawyer, Litigation 10 February 2010 12:012 UTC benzene.legalview.info [Source type: General]
^ Additional tests for patients who have substantial benzene exposure include ECG monitoring, urinalysis, determinations of BUN, creatinine, and liver function test.- ATSDR - MMG: Benzene 10 February 2010 12:012 UTC www.atsdr.cdc.gov [Source type: Academic]
^ However, benzene exposure ha5 failed consistently to induce point mutations, in genotoxicity test systems.- Notice of Intended Changes - Benzene 10 February 2010 12:012 UTC tobaccodocuments.org [Source type: Academic]
.^ The benzene concentration in the tank vapor space increased to a measured peak of 60 parts per million (ppm) during the first pump run test.- DNFSB/TECH-14 10 February 2010 12:012 UTC www.dnfsb.gov [Source type: Academic]
^ For oral exposures, gastric aspiration may be helpful for ingestion of large quantities of benzene, although there is a risk of pulmonary aspiration.- Benzene (PIM 063) 10 February 2010 12:012 UTC www.inchem.org [Source type: Academic]
^ There are reports of retrobulbar neuritis or optic neuritis occurring after inhalation exposure to benzene (Grant & Schuman, 1993).- Benzene (PIM 063) 10 February 2010 12:012 UTC www.inchem.org [Source type: Academic]
.^ Phenol, muconic acid or S-phenyl-N-acetyl cysteine (PhAC), breakdown products of benzene, can be measured in urine to prove benzene exposure.- ATSDR - MMG: Benzene 10 February 2010 12:012 UTC www.atsdr.cdc.gov [Source type: Academic]
^ Sherwood RJ & Carter FWG (1970) The measurement of occupational exposure to benzene vapour.- Benzene (PIM 063) 10 February 2010 12:012 UTC www.inchem.org [Source type: Academic]
^ In order to detect the haematological effects of chronic benzene exposure, it is recommended to follow blood counts at regular intervals.- Benzene (PIM 063) 10 February 2010 12:012 UTC www.inchem.org [Source type: Academic]
.^ Patients who have histories or evidence of substantial exposure and all persons who have ingested benzene should be transported to a medical facility for evaluation.- ATSDR - MMG: Benzene 10 February 2010 12:012 UTC www.atsdr.cdc.gov [Source type: Academic]
^ Otherwise appropriate respiratory protection should be worn at benzene concentrations above occupational exposure limits.- Benzene (PIM 063) 10 February 2010 12:012 UTC www.inchem.org [Source type: Academic]
In the body, benzene is
metabolized.
.^ Phenol, muconic acid or S-phenyl-N-acetyl cysteine (PhAC), breakdown products of benzene, can be measured in urine to prove benzene exposure.- ATSDR - MMG: Benzene 10 February 2010 12:012 UTC www.atsdr.cdc.gov [Source type: Academic]
.^ Other urinary metabolites of benzene can also be used to document exposure.- ATSDR - MMG: Benzene 10 February 2010 12:012 UTC www.atsdr.cdc.gov [Source type: Academic]
^ Management discussion Since the treatment of acute exposure to benzene is limited to decontamination and supportive care, there are few controversies over treatment other than the usual discussion about the risks and benefits of lavage and/or activated charcoal.- Benzene (PIM 063) 10 February 2010 12:012 UTC www.inchem.org [Source type: Academic]
^ Benzene may also be detected in blood for a short period of time after exposure, and it may be measured in exhaled breath.- Benzene (PIM 063) 10 February 2010 12:012 UTC www.inchem.org [Source type: Academic]
.^ Low humidity The ability of a SKC 575-002 Passive Sampler to collect benzene from a relatively dry atmosphere was tested by sampling an atmosphere containing 73.4 mg/m of benzene at an absolute humidity of 1.9 milligrams of water per liter of air (about 10% relative humidity at 22.2C).- Sampling and Analytical Methods: Benzene, 1005 10 February 2010 12:012 UTC www.osha.gov [Source type: Academic]
^ Low concentration The ability of 3M 3520 OVMs to collect benzene at low concentrations was determined by sampling a test atmosphere containing 0.1 times the target concentration of benzene and having an absolute humidity of 15.7 milligrams of water per liter of air (about 80% relative humidity at 22.2C).- Sampling and Analytical Methods: Benzene, 1005 10 February 2010 12:012 UTC www.osha.gov [Source type: Academic]
^ Section 4.9.2 ) Low humidity The ability of a SKC 575-002 Passive Sampler to collect benzene from a relatively dry atmosphere was determined by sampling an atmosphere of two times the target concentration of benzene and having an absolute humidity of 1.9 milligrams of water per liter of air (about 10% relative humidity at 22.2C).- Sampling and Analytical Methods: Benzene, 1005 10 February 2010 12:012 UTC www.osha.gov [Source type: Academic]
The EPA requires that spills or accidental releases into the environment of 10 pounds (4.5 kg) or more of benzene be reported to the EPA.
.^ Occupational Safety and Health Administration: 29 CFR Pan 1910, Occupational Exposure to Benzene; Final Rule.- Notice of Intended Changes - Benzene 10 February 2010 12:012 UTC tobaccodocuments.org [Source type: Academic]
^ OSHA PEL (permissible exposure limit) = 1 ppm (averaged over an 8-hour workshift).- ATSDR - MMG: Benzene 10 February 2010 12:012 UTC www.atsdr.cdc.gov [Source type: Academic]
^ The National Institute for Occupational Safety and Health (NIOSH) recommended exposure limit (REL) is 0.1 ppm (NIOSH, 1990).- Benzene (PIM 063) 10 February 2010 12:012 UTC www.inchem.org [Source type: Academic]
.^ Wash-out effects merely result in short-term extraction from the atmosphere since benzene readily evaporates again from the surface of water or soil.- Benzene 10 February 2010 12:012 UTC www2.gtz.de [Source type: Academic]
^ Chronic exposure of 1 to 25 years at benzene concentrations of 75 ppm has been associated with the development of anemia and leukopenia (Kipen et al., 1989).- Benzene (PIM 063) 10 February 2010 12:012 UTC www.inchem.org [Source type: Academic]
^ Sherwood RJ (1988) Pharmacokinetics of benzene in a human after exposure at about the occupational limit.- Benzene (PIM 063) 10 February 2010 12:012 UTC www.inchem.org [Source type: Academic]
.^ Hudak A & Ungvary G (1978) Embryotoxic effects of benzene and its methyl derivatives: toluene, xylene.- Benzene (PIM 063) 10 February 2010 12:012 UTC www.inchem.org [Source type: Academic]
^ Benzene was previously used widely as a solvent, but this use has decreased in many countries due to the concern over carcinogenic effects.- Benzene (PIM 063) 10 February 2010 12:012 UTC www.inchem.org [Source type: Academic]
^ Haley TJ (1977) Evaluation of the health effects of benzene inhalation.- Benzene (PIM 063) 10 February 2010 12:012 UTC www.inchem.org [Source type: Academic]
Toxic Oil Syndrome caused localised immune-suppression in
Madrid in 1981 from people ingesting
anilide-contaminated
rapeseed oil.
.^ Although in the United States benzene has been removed from commercial solvents, the use of industrial solvents may still be a source of exposure.- Benzene (PIM 063) 10 February 2010 12:012 UTC www.inchem.org [Source type: Academic]
[citation needed]
.^ USES 4.1 Uses 4.1.1 Uses 4.1.2 Description Benzene is used as an intermediate in the manufacture of a number of chemicals, including ethylbenzene (used in the synthesis of styrene), cumene (used in the synthesis of phenol and for the manufacture of phenolic resins and nylon intermediates), cyclohexane (used to make nylon resins), and nitrobenzene (used in the synthesis of aniline).- Benzene (PIM 063) 10 February 2010 12:012 UTC www.inchem.org [Source type: Academic]
^ At present, such uses are minimal; most benzene is consumed in the chemical industry as a raw material for numerous organic chemicals and in plastics manufacture.- Notice of Intended Changes - Benzene 10 February 2010 12:012 UTC tobaccodocuments.org [Source type: Academic]
^ An increased frequency of chromatid and isochromatid breaks was found in children of women exposed during pregnancy to a mix of benzene and other solvents in the printing industry and chemical laboratories (Funes-Cravioto et al., 1977).- Benzene (PIM 063) 10 February 2010 12:012 UTC www.inchem.org [Source type: Academic]
.^ USES 4.1 Uses 4.1.1 Uses 4.1.2 Description Benzene is used as an intermediate in the manufacture of a number of chemicals, including ethylbenzene (used in the synthesis of styrene), cumene (used in the synthesis of phenol and for the manufacture of phenolic resins and nylon intermediates), cyclohexane (used to make nylon resins), and nitrobenzene (used in the synthesis of aniline).- Benzene (PIM 063) 10 February 2010 12:012 UTC www.inchem.org [Source type: Academic]
^ Occupationally exposed populations Individuals working in industries involved with benzene production (petrochemical industry, coke manufacturing), rubber tire or cast rubber film manufacturing, transport or storage of benzene or benzene-containing products, and gas station employees all are at risk for excess benzene exposure (ATSDR, 1993).- Benzene (PIM 063) 10 February 2010 12:012 UTC www.inchem.org [Source type: Academic]
^ Wong O (1987) An industry wide mortality study of chemical workers occupationally exposed to benzene.- Benzene (PIM 063) 10 February 2010 12:012 UTC www.inchem.org [Source type: Academic]
.^ The Occupational Safety and Health Administration (OSHA) recommends monthly blood counts and removal from areas with high benzene exposure for white blood cell counts below 4,000/mm 3 or erythrocyte counts below 4,000,000/mm 3 (OSHA, 1987).- Benzene (PIM 063) 10 February 2010 12:012 UTC www.inchem.org [Source type: Academic]
^ Ott MG, Townsend JC, Fishbeck WA, Langner RA (1978) Mortality among workers occupationally exposed to benzene.- Benzene (PIM 063) 10 February 2010 12:012 UTC www.inchem.org [Source type: Academic]
^ Aksoy M, Erdem S & Dincol G (1974) Leukemia in shoe-workers exposed chronically to benzene.- Benzene (PIM 063) 10 February 2010 12:012 UTC www.inchem.org [Source type: Academic]
.^ Benzene may also be a contaminant in drinking water (ATSDR, 1993).- Benzene (PIM 063) 10 February 2010 12:012 UTC www.inchem.org [Source type: Academic]
.^ Approximately 9,600 kilograms of excess sodium tetraphenylborate in 170,000 gallons of solution decomposed at an unexpectedly rapid rate, generating benzene.- DNFSB/TECH-14 10 February 2010 12:012 UTC www.dnfsb.gov [Source type: Academic]
^ There are different values given, depending on whether both, either, or neither temperature ( T ) or atmospheric pressure ( P ) are known at the sampling site.- Sampling and Analytical Methods: Benzene, 1005 10 February 2010 12:012 UTC www.osha.gov [Source type: Academic]
^ An incubation period of approximately 100 hours was observed before the decomposition reaction proceeded; a maximum rate of 2,000,000 µg/liter-hr was observed.- DNFSB/TECH-14 10 February 2010 12:012 UTC www.dnfsb.gov [Source type: Academic]
.^ Major Uses and Sources of ®ccupational Exposure At one time, benzene was an important solvent.- Notice of Intended Changes - Benzene 10 February 2010 12:012 UTC tobaccodocuments.org [Source type: Academic]
^ Because the benzene has a higher molecular weight compared to air (78 versus 29) or water vapor (18), .- DNFSB/TECH-14 10 February 2010 12:012 UTC www.dnfsb.gov [Source type: Academic]
^ In the United States, smoking accounts for approximately half of the total population exposure to benzene (Wallace, 1989).- Benzene (PIM 063) 10 February 2010 12:012 UTC www.inchem.org [Source type: Academic]
.^ Benzene may also be a contaminant in drinking water (ATSDR, 1993).- Benzene (PIM 063) 10 February 2010 12:012 UTC www.inchem.org [Source type: Academic]
In March 2006, the official
Food Standards Agency in
Britain conducted a survey of 150 brands of soft drinks.
.^ M 3520 OVMs Extraction efficiency The extraction efficiencies of benzene were determined by liquid-spiking four 3M 3520 OVMs, at each concentration level, with the analyte at the RQL to 2 times the target concentration.- Sampling and Analytical Methods: Benzene, 1005 10 February 2010 12:012 UTC www.osha.gov [Source type: Academic]
^ Charcoal tubes Extraction efficiency The extraction efficiencies of benzene were determined by liquid-spiking four charcoal tubes, at each concentration level, with the analyte from the RQL to 2 times the target concentration.- Sampling and Analytical Methods: Benzene, 1005 10 February 2010 12:012 UTC www.osha.gov [Source type: Academic]
^ At an exposure level of 25 ppm of benzene in a sedentary individual, exhaled breath was found to contain 2 ppm of benzene at the end of a 4.5 hour exposure and 0.2 ppm 16 hours later (Sherwood & Carter, 1970).- Benzene (PIM 063) 10 February 2010 12:012 UTC www.inchem.org [Source type: Academic]
The affected batches were removed from sale.
[22] (See also
benzene in soft drinks).
Molecular toxicology
.^ Effort is currently being made toward understanding the mechanisms and kinetics of benzene retention and release.- DNFSB/TECH-14 10 February 2010 12:012 UTC www.dnfsb.gov [Source type: Academic]
^ The goal of the various experimental programs was to characterize the mechanism of benzene generation by understanding its phenomenology, stoichiometry, reaction mechanisms, and kinetics.- DNFSB/TECH-14 10 February 2010 12:012 UTC www.dnfsb.gov [Source type: Academic]
^ This section reviews the potential mechanisms for benzene retention and release, and considers the safety implications of a limited understanding of those mechanisms.- DNFSB/TECH-14 10 February 2010 12:012 UTC www.dnfsb.gov [Source type: Academic]
.^ Summary of clinical effects Acute neurological toxicity from benzene exposure may cause headache, dizziness, drowsiness, confusion, tremors, and loss of consciousness.- Benzene (PIM 063) 10 February 2010 12:012 UTC www.inchem.org [Source type: Academic]
^ After exposure to 63 to 405 mg/m 3 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 (Hunter & Blair, 1972).- Benzene (PIM 063) 10 February 2010 12:012 UTC www.inchem.org [Source type: Academic]
^ Ikeda M & Ohtsuji H (1971) Phenobarbital-induced protection against toxicity of toluene and benzene in the rat.- Benzene (PIM 063) 10 February 2010 12:012 UTC www.inchem.org [Source type: Academic]
.^ Benzene exposure can cause chromosomal aberrations in animals and humans.- Sampling and Analytical Methods: Benzene, 1005 10 February 2010 12:012 UTC www.osha.gov [Source type: Academic]
^ Chronic benzene exposure is associated with an increased risk of leukemia.- Benzene (PIM 063) 10 February 2010 12:012 UTC www.inchem.org [Source type: Academic]
^ Benzene is a myclotoxicant known to suppress bone marrow cell proliferation and to induce hematologic disorders in humans and animals.- Sampling and Analytical Methods: Benzene, 1005 10 February 2010 12:012 UTC www.osha.gov [Source type: Academic]
.^ This modification is essentially an adaptation of sampling probes and gas chromatograph analysis capability used in the depletion of the benzene inventory in Tank 48.- DNFSB/TECH-14 10 February 2010 12:012 UTC www.dnfsb.gov [Source type: Academic]
^ M 3520 OVMs Storage samples for benzene were prepared by collecting samples from a controlled test atmosphere using the recommended sampling conditions.- Sampling and Analytical Methods: Benzene, 1005 10 February 2010 12:012 UTC www.osha.gov [Source type: Academic]
^ Measurement of exhaled benzene has been used to monitor exposure, but is affected by smoking (Brugnone et al., 1989).- Benzene (PIM 063) 10 February 2010 12:012 UTC www.inchem.org [Source type: Academic]
.^ Nakajima T, Okino T, Sato A (1987) Kinetic studies on benzene metabolism in rat liver-possible presence of three forms of benzene metabolizing enzymes in the liver.- Benzene (PIM 063) 10 February 2010 12:012 UTC www.inchem.org [Source type: Academic]
^ Pawar SS & Mungikar AM (1975) Changes in the activities of hepatic drug metabolizing enzymes and lipid peroxidation caused by benzene and toluene.- Benzene (PIM 063) 10 February 2010 12:012 UTC www.inchem.org [Source type: Academic]
.^ For oral exposures, gastric aspiration may be helpful for ingestion of large quantities of benzene, although there is a risk of pulmonary aspiration.- Benzene (PIM 063) 10 February 2010 12:012 UTC www.inchem.org [Source type: Academic]
^ However, there are a multitude of studies on the haematological effects of intermediate and chronic exposure, which include aplastic anaemia, pancytopenia, and varying degrees of thrombocytopenia and leukopenia mediated through bone marrow toxicity.- Benzene (PIM 063) 10 February 2010 12:012 UTC www.inchem.org [Source type: Academic]
^ Additional information on hematological effects of benzene exposure is included under sections 7.3 and 7.5.- Benzene (PIM 063) 10 February 2010 12:012 UTC www.inchem.org [Source type: Academic]
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.
[25]
Summary
.^ PHYSICO-CHEMICAL PROPERTIES 3.1 Origin of the substance Benzene occurs naturally but is primarily produced from petroleum products (ATSDR, 1993).- Benzene (PIM 063) 10 February 2010 12:012 UTC www.inchem.org [Source type: Academic]
^ At present, such uses are minimal; most benzene is consumed in the chemical industry as a raw material for numerous organic chemicals and in plastics manufacture.- Notice of Intended Changes - Benzene 10 February 2010 12:012 UTC tobaccodocuments.org [Source type: Academic]
^ USES 4.1 Uses 4.1.1 Uses 4.1.2 Description Benzene is used as an intermediate in the manufacture of a number of chemicals, including ethylbenzene (used in the synthesis of styrene), cumene (used in the synthesis of phenol and for the manufacture of phenolic resins and nylon intermediates), cyclohexane (used to make nylon resins), and nitrobenzene (used in the synthesis of aniline).- Benzene (PIM 063) 10 February 2010 12:012 UTC www.inchem.org [Source type: Academic]
.^ Absorption by route of exposure .- Benzene (PIM 063) 10 February 2010 12:012 UTC www.inchem.org [Source type: Academic]
^ High risk circumstances of poisoning The most common form of exposure to benzene is occupational, and both occupational and environmental exposures to benzene are overwhelmingly through inhalation.- Benzene (PIM 063) 10 February 2010 12:012 UTC www.inchem.org [Source type: Academic]
^ For a worker exposed to 10 ppm of ambient benzene with his entire skin exposed, and 100 cm2 of skin exposed directly to 5% benzene (gasoline), the expected hourly absorption of benzene will be 7.5 L from inhalation, 1.5 L from ambient skin absorption, and 7.0 L from direct skin contact with the liquid (Blank & McAuliffe, 1985).- Benzene (PIM 063) 10 February 2010 12:012 UTC www.inchem.org [Source type: Academic]
.^ Metabolism Benzene is both exhaled unchanged in the lungs and excreted as metabolites in the urine.- Benzene (PIM 063) 10 February 2010 12:012 UTC www.inchem.org [Source type: Academic]
^ After exposure to 63 to 405 mg/m 3 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 (Hunter & Blair, 1972).- Benzene (PIM 063) 10 February 2010 12:012 UTC www.inchem.org [Source type: Academic]
^ Pawar SS & Mungikar AM (1975) Changes in the activities of hepatic drug metabolizing enzymes and lipid peroxidation caused by benzene and toluene.- Benzene (PIM 063) 10 February 2010 12:012 UTC www.inchem.org [Source type: Academic]
.^ This modification is essentially an adaptation of sampling probes and gas chromatograph analysis capability used in the depletion of the benzene inventory in Tank 48.- DNFSB/TECH-14 10 February 2010 12:012 UTC www.dnfsb.gov [Source type: Academic]
^ Breath samples for benzene are collected in standard breath sampling tubes on a solid sorbent such as activated charcoal, silica gel, or Tenax GC (ATSDR, 1993).- Benzene (PIM 063) 10 February 2010 12:012 UTC www.inchem.org [Source type: Academic]
^ Catechol is produced via this pathway through the intermediate benzene glycol, and is excreted as a glucuronide or sulfate conjugate (Henderson et al., 1989).- Benzene (PIM 063) 10 February 2010 12:012 UTC www.inchem.org [Source type: Academic]
.^ Morimoto K, Wolff S, Koizumi A (1983) Induction of sister-chromatid exchanges in human lymphocytes by microsomal activation of benzene metabolites.- Benzene (PIM 063) 10 February 2010 12:012 UTC www.inchem.org [Source type: Academic]
^ The benzene concentration in the tank vapor space increased to a measured peak of 60 parts per million (ppm) during the first pump run test.- DNFSB/TECH-14 10 February 2010 12:012 UTC www.dnfsb.gov [Source type: Academic]
^ Sherwood RJ (1988) Pharmacokinetics of benzene in a human after exposure at about the occupational limit.- Benzene (PIM 063) 10 February 2010 12:012 UTC www.inchem.org [Source type: Academic]
[26]
Biological oxidation and carcinogenic activity
.^ This laboratory test of different batch compositions could be implemented in the short term until a fuller understanding of the effect of slurry composition on benzene generation rate is achieved.- DNFSB/TECH-14 10 February 2010 12:012 UTC www.dnfsb.gov [Source type: Academic]
^ Benzene was previously used widely as a solvent, but this use has decreased in many countries due to the concern over carcinogenic effects.- Benzene (PIM 063) 10 February 2010 12:012 UTC www.inchem.org [Source type: Academic]
.^ Catechol is produced via this pathway through the intermediate benzene glycol, and is excreted as a glucuronide or sulfate conjugate (Henderson et al., 1989).- Benzene (PIM 063) 10 February 2010 12:012 UTC www.inchem.org [Source type: Academic]
^ The first step in benzene metabolism is the formation of benzene oxide, an epoxide, by cytochrome P-450 dependent mixed function oxidases.- Benzene (PIM 063) 10 February 2010 12:012 UTC www.inchem.org [Source type: Academic]
See also
References
- ^ David R. Lide, ed.. ""Physical Constants of Organic Compounds", in CRC Handbook of Chemistry and Physics, Internet Version 2005, <http://www.hbcpnetbase.com>". CRC Press.
- ^ a b A. J. Rocke (1985). "Hypothesis and Experiment in the Early Development of Kekule's Benzene Theory". Annals of Science 42: 355–81. doi:10.1080/00033798500200411.
- ^ M. Faraday (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 of London 115: 440–466. doi:10.1098/rstl.1825.0022. http://links.jstor.org/sici?sici=0261-0523%281825%29115%3C440%3AONCOCA%3E2.0.CO%3B2-B.
- ^ R. Kaiser (1968). "Bicarburet of Hydrogen. Reappraisal of the Discovery of Benzene in 1825 with the Analytical Methods of 1968". Angewandte Chemie International Edition in English 7 (5): 345–350. doi:10.1002/anie.196803451.
- ^ E. Mitscherlich (1834). "Ueber das Benzol und die Säuren der Oel- und Talgarten". Annalen der Pharmacie 9 (1): 39–48. doi:10.1002/jlac.18340090103.
- ^ F. A. Kekulé (1865). "Sur la constitution des substances aromatiques". Bulletin de la Societe Chimique de Paris 3: 98–110.
- ^ F. A. Kekulé (1866). "Untersuchungen uber aromatische Verbindungen". Liebigs Annalen der Chemie 137: 129–36. doi:10.1002/jlac.18661370202.
- ^ Translated into English by D. Wilcox and F. Greenbaum, Journal of Chemical Education, 42 (1965), 266–67.
- ^ F. A. Kekulé (1890). "Benzolfest: Rede". Berichte der Deutschen Chemischen Gesellschaft 23: 1302–11. doi:10.1002/cber.189002301204. http://gallica.bnf.fr/ark:/12148/bpt6k90720c/f1304.chemindefer.
- ^ O. T. Benfey, "August Kekulé and the Birth of the Structural Theory of Organic Chemistry in 1858," Journal of Chemical Education, 35 (1958), 21–23
- ^ Jean Gillis, "Auguste Kekulé et son oeuvre, realisee a Gand de 1858 a 1867," Memoires de l'Academie Royale de Belgique, 37:1 (1866), 1–40.
- ^ K. Lonsdale (1929). "The Structure of the Benzene Ring in Hexamethylbenzene". Proceedings of the Royal Society 123A: 494.
- ^ K. Lonsdale (1931). "An X-Ray Analysis of the Structure of Hexachlorobenzene, Using the Fourier Method". Proceedings of the Royal Society 133A: 536–553. http://gallica.bnf.fr/ark:/12148/bpt6k56226p/f558.table.
- ^ bonding in benzene - the Kekulé structure
- ^ "Unicode Character 'BENZENE RING' (U+232C)". http://www.fileformat.info/info/unicode/char/232c/index.htm. Retrieved 2009-01-16.
- ^ "Unicode Character 'BENZENE RING WITH CIRCLE' (U+23E3)". http://www.fileformat.info/info/unicode/char/23e3/index.htm. Retrieved 2009-01-16.
- ^ Kolmetz, Gentry, Guidelines for BTX Revamps, AIChE 2007 Spring Conference
- ^ [http://www.epa.gov/EPA-AIR/2006/March/Day-29/a2315b.htm "Control of Hazardous Air Pollutants From Mobile Sources"]. U.S. Environmental Protection Agency. 2006-03-29. pp. 15853. http://www.epa.gov/EPA-AIR/2006/March/Day-29/a2315b.htm. Retrieved 2008-06-27.
- ^ ToxFAQs for Benzene, Agency for Toxic Substances and Disease Registry, Department of Health and Human Services
- ^ Huff J (Apr-Jun 2007). "Benzene-induced cancers: abridged history and occupational health impact". Int J Occup Environ Health 13 (2): 213–21. PMID 17718179.
- ^ Rana SV; Verma Y (April 2005). "Biochemical toxicity of benzene". J Environ Biol 26 (2): 157–68. PMID 16161967.
- ^ "FDA: Too Much Benzene In Some Drinks", CBS News, May 19, 2006, retrieved July 11, 2006
- ^ Fracasso, M.E. (2009). "Low air levels of benzene: Correlation between biomarkers of exposure and genotoxic effects". Toxicol Lett [Epub ahead of print] (May 7). }
- ^ *Eastmond, D.A. (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 probes". Mutat Res 322 (1): pp. 9–20. }
- ^ *Garte, S (2000). "Genetic susceptibility to benzene toxicity in humans". J Toxicol Environ Health A 71 (22): pp. 1482–1489. }
- ^ Agency for Toxic Substances and Disease Registry. (2007). Benzene: Patient information sheet.
External links
.^ NIOSH (1990) NIOSH Pocket Guide to Chemical Hazards, DHHS (NIOSH) Publication No, 90-117.- Benzene (PIM 063) 10 February 2010 12:012 UTC www.inchem.org [Source type: Academic]
^ At present, such uses are minimal; most benzene is consumed in the chemical industry as a raw material for numerous organic chemicals and in plastics manufacture.- Notice of Intended Changes - Benzene 10 February 2010 12:012 UTC tobaccodocuments.org [Source type: Academic]
^ BENZENE International Programme on Chemical Safety Poisons Information Monogaph 63 Chemical 1.- Benzene (PIM 063) 10 February 2010 12:012 UTC www.inchem.org [Source type: Academic]
of Health and Human Services: TR-289: Toxicology and Carcinogenesis Studies of Benzene
Video Podcast of Sir John Cadogan giving a lecture on Benzene since Faraday, in 1991
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