Editing Xylene

{{Short description|Organic compounds with the formula (CH3)2C6H4}}
[[File:IUPAC-cyclic.svg|thumb|400px|The three xylene isomers: [[o-Xylene|''o''-xylene]], [[m-Xylene|''m''-xylene]], and [[p-Xylene|''p''-xylene]]]]

In [[organic chemistry]], '''xylene''' or '''xylol''' ({{ety|el|''ξύλον'' (xylon)|wood}};<ref>{{LSJ|cu/lon1|ξύλον|ref}}.</ref><ref>{{OEtymD|xylene}}</ref> [[IUPAC name]]: '''dimethylbenzene''') are any of three [[organic compound]]s with the formula {{chem2|(CH3)2C6H4}}. They are derived from the substitution of two [[hydrogen]] atoms with [[methyl group]]s in a [[benzene]] ring; which hydrogens are substituted determines which of three [[structural isomers]] results. It is a colorless, flammable, slightly greasy liquid of great industrial value.<ref name="Ullmann"/>  

The mixture is referred to as both xylene and, more precisely, xylenes. '''Mixed xylenes''' refers to a mixture of the xylenes plus [[ethylbenzene]]. The four compounds have identical [[molecular formulas]] {{chem2|C8H10}}. Typically the four compounds are produced together by various [[catalytic reforming]] and [[pyrolysis]] methods.<ref>{{cite book |doi=10.1002/0471238961.2425120503011414.a01 |chapter=Xylenes and Ethylbenzene |title=Kirk-Othmer Encyclopedia of Chemical Technology |year=2000 |last1=Cannella |first1=William J. |isbn=0471238961}}</ref>

==Occurrence and production==
Xylenes are an important [[petrochemical]] produced by [[catalytic reforming]] and also by [[carbonization|coal carbonisation]] in the manufacture of [[coke (fuel)|coke fuel]]. They also occur in crude oil in concentrations of about 0.5–1%, depending on the source. Small quantities occur in [[gasoline]] and [[jet fuel|aircraft fuel]]s.

Xylenes are produced mainly as part of the [[BTX (chemistry)|BTX]] aromatics ([[benzene]], [[toluene]], and xylenes) extracted from the product of [[catalytic reforming]] known as [[reformate]].

Several million tons are produced annually.<ref name="Ullmann">{{Cite book | doi=10.1002/14356007.a28_433|chapter = Xylenes|title = Ullmann's Encyclopedia of Industrial Chemistry|year = 2000|last1 = Fabri|first1 = Jörg| last2=Graeser| first2=Ulrich| last3=Simo| first3=Thomas A.| isbn=978-3527306732}}</ref> In 2011, a global consortium began construction of one of the world's largest xylene plants in [[Singapore]].<ref>{{cite journal | doi = 10.1021/cen-v089n038.p018 | title = Making Aromatics in Singapore | journal = Chemical & Engineering News Archive | volume = 89 | issue = 38 | pages = 18–19 | year = 2011 | last1 = Tremblay | first1 = Jean-François }}</ref>

==History==
Xylene was first isolated and named in 1850 by the French chemist [[Auguste André Thomas Cahours|Auguste Cahours]] (1813–1891), having been discovered as a constituent of [[wood tar]].<ref>Cahours, Auguste (1850) [http://gallica.bnf.fr/ark:/12148/bpt6k2987x/f319.image.langEN "Recherches sur les huiles légéres obtenues dans la distillation du bois"] (Investigations of light oils obtained by the distillation of wood), ''Compte rendus'', '''30''' : 319-323; see especially p. 321.  From p. 321:  ''"Je le désignerai sous le nomme ''xylène''."'' (I will designate it by the name of ''xylene''.)  Note:  Cahours' empirical formula for xylene is incorrect because chemists at that time used the wrong atomic mass for carbon (6 instead of 12).</ref>

==Industrial production==
Xylenes are produced by the [[methylation]] of [[toluene]] and [[benzene]].<ref name="Ullmann" /><ref>Martindale, David C. and Kuchar, Paul J., [https://web.archive.org/web/20180717100321/http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&p=1&u=/netahtml/PTO/search-bool.html&r=1&f=G&l=50&co1=AND&d=PTXT&s1=5043502.PN.&OS=PN/5043502&RS=PN/5043502 Production of xylenes from light aliphatic hydrocarbons via dehydrocyclodimerization and methylation], United States Patent No. 5,043,502, 1991-8-27. Accessed 2012-4-28.</ref> Commercial or [[chemical purity|laboratory-grade]] xylene produced usually contains about 40–65% of [[m-Xylene|''m''-xylene]] and up to 20% each of [[o-Xylene|''o''-xylene]], [[p-Xylene|''p''-xylene]] and [[ethylbenzene]].<ref>{{cite web |title=Xylene (Mixed Isomers), Air Toxic Hazard Summary |url=http://www.epa.gov/airtoxics/hlthef/xylenes.html |publisher=United States Environmental Protection Agency |access-date=8 February 2015}}</ref><ref name="Kandyala">{{cite journal | last1 = Kandyala | first1 = Reena | last2 = Raghavendra | first2 = Sumanth Phani C. | last3 = Rajasekharan | first3 = Saraswathi T. | year = 2010 | title = Xylene: An overview of its health hazards and preventive measures | journal = J Oral Maxillofac Pathol | volume = 14 | issue = 1| pages = 1–5 | doi = 10.4103/0973-029X.64299 | pmid = 21180450 | pmc=2996004 | doi-access = free }}</ref><ref name="Sweden">[http://apps.kemi.se/flodessok/floden/kemamne_eng/xylen_eng.htm Xylene] ({{webarchive |url=https://web.archive.org/web/20110811152832/http://apps.kemi.se/flodessok/floden/kemamne_eng/xylen_eng.htm |date=August 11, 2011 }}), Swedish Chemicals Agency, apps.kemi.se, 2010. Accessed 2012-4-28.</ref> The ratio of isomers can be shifted to favor the highly valued ''p''-xylene via the patented UOP-''Isomar'' process<ref>{{cite web |title=Capturing Opportunities for ''Para''-xylene Production |url=http://www.uop.com/?document=uop-capturing-opportunities-for-para-xylene-production-tech-paper&download=1 |publisher=UOP, A Honeywell Company |access-date=8 February 2015}}</ref> or by [[transalkylation]] of xylene with itself or trimethylbenzene. These conversions are catalyzed by [[zeolite]]s.<ref name="Ullmann" />

[[ZSM-5]] is used to facilitate some isomerization reactions leading to mass production of modern plastics.

==Properties==
The physical properties of the isomers of xylene differ slightly. The melting point ranges from {{convert|−47.87|°C|°F|2}} (''m''-xylene) to {{convert|13.26|°C|°F|2}} (''p''-xylene)—as usual, the para isomer's melting point is much higher because it packs more readily in the crystal structure. The boiling point for each isomer is around {{convert|140|°C|°F|0}}. The density of each isomer is around {{convert|0.87|g/mL|lb/gal lb/impgal|abbr=on}} and thus is less dense than [[properties of water|water]]. The odor of xylene is detectable at concentrations as low as 0.08 to 3.7&nbsp;ppm (parts of xylene per million parts of air) and can be tasted in water at 0.53 to 1.8&nbsp;ppm.<ref name="Kandyala" />

<!-- Here is a table of data; skip past it to edit the text. -->
{| align="center" class="wikitable" style="background:white; border-color:#C0C090; text-align:center;"

! {{Chemical datatable header}} colspan="5" | Xylene isomers
|-
<!--| align="center" colspan="5" | [[Image:Xylene Isomers.PNG|400px|{{PAGENAME}}]] replace if not identical with the pagename -->
|-
! {{Chemical datatable header}} colspan="5" | General
|- style="font-weight:bold;"
| Common name
| Xylenes<br>(mixture)
| [[o-Xylene|''o''-Xylene]]
| [[m-Xylene|''m''-Xylene]]
| [[p-Xylene|''p''-Xylene]]
|-
| [[IUPAC nomenclature|Systematic name]]
| Dimethylbenzene
| 1,2-Dimethylbenzene
| 1,3-Dimethylbenzene
| 1,4-Dimethylbenzene
|-
| Other names
| Xylol
| ''o''-Xylol;<br>Orthoxylene
| ''m''-Xylol;<br>Metaxylene
| ''p''-Xylol;<br>Paraxylene
|-
| [[Chemical formula|Molecular formula]]
| colspan="4" | C<sub>8</sub>H<sub>10</sub>
|-
| [[Simplified molecular input line entry specification|SMILES]]
|
| Cc1c(C)cccc1
| Cc1cc(C)ccc1
| Cc1ccc(C)cc1
|-
| [[Molar mass]]
| colspan="4" | 106.16&nbsp;g/mol
|-
| Appearance
| colspan="4" | Clear, colorless liquid
|-
| [[CAS registry number|CAS number]]
| [1330-20-7]
| [95-47-6]
| [108-38-3]
| [106-42-3]
|-
! {{Chemical datatable header}} colspan="5" | Properties
|-
| [[Density]] and [[phase (matter)|phase]]
| 0.864&nbsp;g/mL, liquid
| 0.88&nbsp;g/mL, liquid
| 0.86&nbsp;g/mL, liquid
| 0.86&nbsp;g/mL, liquid
|-
| [[Soluble|Solubility]] in water
| colspan="4" | Practically insoluble
|-
| colspan="5" | Soluble in non-polar solvents such as [[aromatic hydrocarbon]]s
|-
| [[Melting point]]
| −47.4&nbsp;°C (−53.3&nbsp;°F; 226 K)
| −25&nbsp;°C (−13&nbsp;°F; 248 K)
| −48&nbsp;°C (−54&nbsp;°F; 225 K)
| 13&nbsp;°C (55&nbsp;°F; 286 K)
|-
| [[Boiling point]]
| 138.5&nbsp;°C (281.3&nbsp;°F; 412 K)
| 144&nbsp;°C (291&nbsp;°F; 417 K)
| 139&nbsp;°C (282&nbsp;°F; 412 K)
| 138&nbsp;°C (280&nbsp;°F; 411 K)
|-
| [[Viscosity]]
|
| 0.812 c[[Poise (unit)|P]] at {{convert|20|°C|°F|0}}
| 0.62 c[[Poise (unit)|P]] at {{convert|20|°C|°F|0}}
| 0.34 c[[Poise (unit)|P]] at {{convert|30|°C|°F|0}}
|-
! {{Chemical datatable header}} colspan="5" | Hazards <!-- Summary only- MSDS entry provides more complete information -->
|-
| [[Safety data sheet|SDS]]
| [https://www.fishersci.com/store/msds?partNumber=X5FB50&productDescription=XYLENES+ACS+FB+50L&vendorId=VN00033897&countryCode=US&language=en Xylenes]
| [https://fscimage.fishersci.com/msds/17180.htm ''o''-Xylene]
| [https://fscimage.fishersci.com/msds/95260.htm ''m''-Xylene]
| [https://fscimage.fishersci.com/msds/95257.htm ''p''-Xylene]
|-
| [[GHS hazard pictograms|EU pictograms]]
| colspan="4" | {{GHS02}}{{GHS07}}{{GHS08}}

 
|-
| [[NFPA 704]]
| colspan="4" | {{NFPA 704 diamond| H=2 | F=3 | R=0 }}
|-
| [[Flash point]]
| {{convert|30|°C|°F|0}}
| {{convert|17|°C|°F|0}}
| {{convert|25|°C|°F|0}}
| {{convert|25|°C|°F|0}}
|-
| [[GHS hazard statements|H]] & [[GHS precautionary statements|P phrases]]
| colspan="4" | {{H-phrases|225|226|304|312|315|319|332|335|412}}<br/>
{{P-phrases|210|233|240|241|242|243|261|264|271|273|280
|301+310|302+352|303+361+353|304+312|304+340|305+351+338|312|321|322|331|332+313|337+313|362|363|370+378
|403+233|403+235|405|501}}
|-
| [[RTECS]] number
|
| ZE2450000
| ZE2275000
| ZE2625000
|-
! {{Chemical datatable header}} colspan="5" | Related compounds
|-
| Related aromatic<br>hydrocarbons
| colspan="4" | [[Toluene]], [[mesitylene]], [[benzene]], [[ethylbenzene]]
|-
| Related compounds
| colspan="4" | Xylenols – types of [[phenols]]
|-
| {{Chemical datatable header}} colspan="5" | <small>Except where noted otherwise, data are given for materials in their [[standard state|standard state (at 25{{nbsp}}°C, 100{{nbsp}}kPa)]]<br/>[[wikipedia:Chemical infobox|Infobox disclaimer and references]]</small>
|}

Xylenes form [[azeotrope]]s with water and a variety of alcohols. The azeotrope with water consists of 60% xylenes and boils at 94.5&nbsp;°C.<ref name="Ullmann" /> As with many [[alkylbenzene]] compounds, xylenes form complexes with various [[halocarbon]]s.<ref>{{cite journal |title= Separation of Xylenes |journal= Ind. Eng. Chem. |year= 1955 |volume= 47 |issue= 2 |pages= 250–253 |doi= 10.1021/ie50542a028 |author1=Clark J. E. |author2=Luthy, R. V. }}</ref> The complexes of different isomers often have dramatically different properties from each other.<ref>{{cite journal |doi = 10.1021/ac980221b |title = Separation of Closely Boiling Isomers and Identically Boiling Isotopomers via Electron-Transfer-Assisted Extraction |journal = Analytical Chemistry |volume = 70 |issue = 18 |pages = 3880 |year = 1998 |last1 = Stevenson |first1 = Cheryl D. |last2 = McElheny |first2 = Daniel J. |last3 = Kage |first3 = David E. |last4 = Ciszewski |first4 = James T. |last5 = Reiter |first5 = Richard C.}}</ref>

==Applications==

===Terephthalic acid and related derivatives===
''p''-Xylene is the principal precursor to [[terephthalic acid]] and [[dimethyl terephthalate]], both [[monomer]]s used in the production of [[polyethylene terephthalate]] (PET) [[plastic bottle]]s and [[polyester]] clothing. 98% of ''p''-xylene production, and half of all xylenes produced is consumed in this manner.<ref name="Sweden" /><ref>ICIS, [http://www.icis.com/chemicals/paraxylene-orthoxylene/ Paraxylene-Orthoxylene {{pipe}} Prices, News & Market Analysis], icis.com, 2012. Accessed 2012-04-28.</ref> ''o''-Xylene is an important precursor to [[phthalic anhydride]]. The demand for [[isophthalic acid]] is relatively modest, so ''m''-xylene is rarely sought (and hence the utility of its conversion to the ''o''- and ''p''-isomers).

===Solvent applications and industrial purposes ===
Xylenes are used as a solvent in [[printing]], [[rubber]], and [[leather]] industries. It is a common component of ink, [[rubber]], and [[adhesive]]s.<ref>Bostik, [http://www.bostik-amer.com/upload/download/MSDS%20Blu%20Tack.pdf Safety Data Sheet Blu-Tack] ({{webarchive |url=https://web.archive.org/web/20110911020151/http://www.bostik-amer.com/upload/download/MSDS%20Blu%20Tack.pdf |date=September 11, 2011 }}), No. 13135, Bostik Corp., June 2007. Accessed 2012-04-28.</ref> In thinning [[paint]]s and [[varnish]]es, it can be substituted for [[toluene]] where slower drying is desired, and thus is used by [[conservator-restorer|conservators]] of art objects in solubility testing.<ref>Samet, Wendy, (comp.), [http://www.conservation-wiki.com/index.php?title=Appendix_I Appendix I, Painting Conservation Catalog], American Institute for Conservation of Historic and Artistic Works, conservation-wiki.com, September 1997. Accessed 2012-04-28.</ref> Similarly it is a [[cleaning agent]], e.g., for [[steel]], [[silicon wafer]]s, and [[integrated circuit]]s. In dentistry, xylene can be used to dissolve [[gutta percha]], a material used for endodontics (root-canal treatments). In the petroleum industry, xylene is also a frequent component of paraffin solvents, used when the tubing becomes clogged with paraffin wax.

===Laboratory use===
Xylene is used in the laboratory to make baths with dry ice to cool reaction vessels,<ref>{{cite web |title=Cooling baths |url=http://chemwiki.ucdavis.edu/Reference/Lab_Techniques/Cooling_baths |publisher=UC Davis Chem Wiki |access-date=8 February 2015 |date=2013-10-02 |archive-date=2015-02-08 |archive-url=https://web.archive.org/web/20150208042031/http://chemwiki.ucdavis.edu/Reference/Lab_Techniques/Cooling_baths |url-status=dead }}</ref> and as a [[solvent]] to remove synthetic [[immersion oil]] from the microscope [[objective (optics)|objective]] in [[optical microscope|light microscopy]].<ref>{{Citation |last = Cargille |first = John |title = Immersion Oil and the Microscope |journal = New York Microscopical Society Yearbook |orig-year = 1964 |year = 1985 |url = http://www.cargille.com/immersionoilmicroscope.shtml |access-date = 2011-03-10 |archive-url = https://web.archive.org/web/20110911190610/http://www.cargille.com/immersionoilmicroscope.shtml |archive-date = 2011-09-11 |url-status = dead }}</ref> In [[histology]], xylene is the most widely used clearing agent.<ref>{{cite book |title=Histotechnology: A Self-Instructional Text |last1=Carson |first1=Freida |last2=Hladik |first2=Christa |edition=3 |year=2009 |publisher=[[American Society for Clinical Pathology]] Press |isbn=9780891895817 |page=35 }}</ref> Xylene is used to remove paraffin from dried microscope slides prior to staining. After staining, microscope slides are put in xylene prior to mounting with a coverslip.

===Precursor to other compounds===
In one large-scale application, para-xylene is converted to [[terephthalic acid]]. The major application of ortho-xylene is as a precursor to [[phthalate ester]]s, used as [[plasticizer]]. Meta-xylene is converted to [[isophthalic acid]] derivatives, which are components of [[alkyd resin]]s.<ref name="Ullmann"/>

==Chemical properties==
Generally, two kinds of reactions occur with xylenes: those involving the methyl groups and those involving the ring C–H bonds.  Being benzylic and hence weakened, the C–H bonds of the methyl groups are susceptible to free-radical reactions, including halogenation to the corresponding [[xylene dichloride]]s (bis(chloromethyl)benzenes), while [[Free-radical halogenation|mono-bromination]] yields [[xylyl bromide]], a [[tear gas]] agent. Oxidation and [[ammoxidation]] also target the methyl groups, affording dicarboxylic acids and the dinitriles. Electrophiles attack the aromatic ring, leading to chloro- and nitroxylenes.<ref name="Ullmann"/>

==Health and safety==
Xylene is flammable but of modest acute toxicity, with {{LD50}} ranges from 200 to 5000&nbsp;mg/kg for animals. Oral {{LD50}} for rats is 4300&nbsp;mg/kg. The principal mechanism of detoxification is oxidation to [[toluic acid|methylbenzoic acid]] and hydroxylation to hydroxylene.<ref name="Ullmann" />

The main effect of inhaling xylene vapor is [[CNS depression|depression of the central nervous system]] (CNS), with symptoms such as headache, dizziness, nausea and vomiting. At an exposure of 100&nbsp;ppm, one may experience nausea or a headache. At an exposure between 200 and 500&nbsp;ppm, symptoms can include feeling "high", dizziness, weakness, irritability, vomiting, and slowed reaction time.<ref name=":0">{{Cite journal |title = Xylene: An overview of its health hazards and preventive measures |journal = Journal of Oral and Maxillofacial Pathology |date = 2010-01-01 |issn = 0973-029X |pmc = 2996004 |pmid = 21180450 |pages = 1–5 |volume = 14 |issue = 1 |doi = 10.4103/0973-029X.64299 |first1 = Reena |last1 = Kandyala |first2 = Sumanth Phani C. |last2 = Raghavendra |first3 = Saraswathi T. |last3 = Rajasekharan |doi-access = free }}</ref><ref>{{Cite web |url=http://oehha.ca.gov/air/acute_rels/pdf/XylenesA.pdf |title=ACUTE TOXICITY SUMMARY: XYLENES |url-status=dead |archive-url=https://web.archive.org/web/20151022131350/http://www.oehha.ca.gov/air/acute_rels/pdf/xylenesA.pdf |archive-date=October 22, 2015 }}</ref>

The side effects of exposure to low concentrations of xylene ({{nowrap|< 200 ppm}}) are reversible and do not cause permanent damage. Long-term exposure may lead to headaches, irritability, depression, insomnia, agitation, extreme tiredness, tremors, hearing loss, impaired concentration and short-term memory loss.<ref>{{Cite web | url=http://www.inchem.org/documents/ehc/ehc/ehc190.htm | title=Xylenes (EHC 190, 1997)}}</ref>{{clarify |reason=short-term memory loss? |date=June 2016}} A condition called [[chronic solvent-induced encephalopathy]], commonly known as "organic-solvent syndrome" has been associated with xylene exposure. There is very little information available that isolates xylene from other solvent exposures in the examination of these effects.<ref name=":0" />

Hearing disorders have been also linked to xylene exposure, both from studies with experimental animals,<ref>{{Cite journal |last1=Gagnaire |first1=F. |last2=Marignac |first2=B. |last3=Langlais |first3=C. |last4=Bonnet |first4=P. |date=July 2001 |title=Ototoxicity in rats exposed to ortho-, meta- and para-xylene vapours for 13 weeks |journal=Pharmacology & Toxicology |volume=89 |issue=1 |pages=6–14 |doi=10.1034/j.1600-0773.2001.d01-129.x |doi-broken-date=15 February 2025 |issn=0901-9928 |pmid=11484912}}</ref><ref>{{Cite journal |last1=Gagnaire |first1=F. |last2=Marignac |first2=B. |last3=Blachère |first3=V. |last4=Grossmann |first4=S. |last5=Langlais |first5=C. |date=2007-03-07 |title=The role of toxicokinetics in xylene-induced ototoxicity in the rat and guinea pig |journal=Toxicology |volume=231 |issue=2–3 |pages=147–158 |doi=10.1016/j.tox.2006.11.075 |issn=0300-483X |pmid=17210216|bibcode=2007Toxgy.231..147G }}</ref> as well as clinical studies.<ref>{{Cite journal |last1=Fuente |first1=Adrian |last2=McPherson |first2=Bradley |last3=Cardemil |first3=Felipe |date=September 2013 |title=Xylene-induced auditory dysfunction in humans |journal=Ear and Hearing |volume=34 |issue=5 |pages=651–660 |doi=10.1097/AUD.0b013e31828d27d7 |issn=1538-4667 |pmid=23598724|s2cid=45206975 |hdl=10533/134303 |hdl-access=free }}</ref><ref>{{Cite journal |last1=Draper |first1=T. H. J. |last2=Bamiou |first2=D.-E. |date=April 2009 |title=Auditory neuropathy in a patient exposed to xylene: case report |journal=The Journal of Laryngology & Otology |volume=123 |issue=4 |pages=462–465 |doi=10.1017/S0022215108002399 |pmid=18439334 |issn=1748-5460|url=http://discovery.ucl.ac.uk/70543/1/S0022215108002399.pdf |archive-url=https://web.archive.org/web/20170809163223/http://discovery.ucl.ac.uk/70543/1/S0022215108002399.pdf |archive-date=2017-08-09 |url-status=live }}</ref><ref>{{Cite journal |last1=Fuente |first1=Adrian |last2=McPherson |first2=Bradley |last3=Hood |first3=Linda J. |date=November 2012 |title=Hearing loss associated with xylene exposure in a laboratory worker |journal=Journal of the American Academy of Audiology |volume=23 |issue=10 |pages=824–830 |doi=10.3766/jaaa.23.10.7 |issn=1050-0545 |pmid=23169198|hdl=10533/137495 |hdl-access=free }}</ref>

Xylene is also a skin irritant and strips the skin of its oils, making it more permeable to other chemicals. The use of impervious gloves and masks, along with respirators where appropriate, is recommended to avoid occupational health issues from xylene exposure.<ref name=":0" />

Xylenes are metabolized to [[methylhippuric acid]]s.<ref name=NIOSH>{{cite web | url = https://www.cdc.gov/niosh/docs/2003-154/pdfs/8301.pdf | work = NIOSH Manual of Analytical Methods (NMAM) | edition = Fourth | title = HIPPURIC and METHYL HIPPURIC ACIDS in urine }}<!-- also found at https://en.wikisource.org/wiki/Hippuric_and_Methyl_Hippuric_Acids_in_Urine_(8301) --></ref><ref name=Inoue>{{Cite journal |pmid = 8482596 |year = 1993 |last1 = Inoue |first1 = O. |title = Excretion of methylhippuric acids in urine of workers exposed to a xylene mixture: Comparison among three xylene isomers and toluene |journal = International Archives of Occupational and Environmental Health |volume = 64 |issue = 7 |pages = 533–539 |last2 = Seiji |first2 = K. |last3 = Kawai |first3 = T. |last4 = Watanabe |first4 = T. |last5 = Jin |first5 = C. |last6 = Cai |first6 = S. X. |last7 = Chen |first7 = Z. |last8 = Qu |first8 = Q. S. |last9 = Zhang |first9 = T. |last10 = Ikeda |first10 = M. |doi=10.1007/bf00381104|bibcode = 1993IAOEH..64..533I |s2cid = 21534640 }}</ref> The presence of methylhippuric acid can be used as a [[biomarker]] to determine exposure to xylene.<ref name=Inoue/><ref>{{Cite journal | author = Kira S. | title = Measurement by gas chromatography of urinary hippuric acid and methylhippuric acid as indices of toluene and xylene exposure | journal = Occupational and Environmental Medicine | date = 1977 | volume = 34 | issue = 305–309 | pages = 305–309 | doi = 10.1136/oem.34.4.305 | pmid = 588486 | pmc = 1008281 }}</ref>

==See also==
* [[Alkylbenzene]]
* [[C2-Benzenes]]
* [[Hydrodealkylation]]
* [[Transalkylation]]
* [[Xylene cyanol]]

==References==
{{Reflist|30em}}

==External links==
{{commons category|Xylenes}}
*{{Cite EB1911|wstitle=Xylene}}
*[https://www.cdc.gov/niosh/npg/npgd0668.html NIOSH Pocket Guide to Chemical Hazards] (''o''-Xylene)
*[https://www.cdc.gov/niosh/npg/npgd0669.html NIOSH Pocket Guide to Chemical Hazards] (''m''-Xylene)
*[https://www.cdc.gov/niosh/npg/npgd0670.html NIOSH Pocket Guide to Chemical Hazards] (''p''-Xylene)
*[https://www.epa.gov/haps/health-effects-notebook-hazardous-air-pollutants Xylene, Hazard Summary (EPA)] (Mixed Isomers)
*[https://synergist.aiha.org/201811-the-ear-poisons The Ear Poisons], ''The Synergist'', [[American Industrial Hygiene Association]], November, 2018

{{Hydrocarbons}}
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