Xylene
In
The mixture is referred to as both xylene and, more precisely, xylenes. Mixed xylenes refers to a mixture of the xylenes plus
Occurrence and production
Xylenes are an important petrochemical produced by catalytic reforming and also by coal carbonisation in the manufacture of 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 aircraft fuels.
Xylenes are produced mainly as part of the
Several million tons are produced annually.[3] In 2011, a global consortium began construction of one of the world's largest xylene plants in Singapore.[5]
History
Xylene was first isolated and named in 1850 by the French chemist
Industrial production
Xylenes are produced by the methylation of toluene and benzene.[3][7] Commercial or laboratory-grade xylene produced usually contains about 40–65% of m-xylene and up to 20% each of o-xylene, p-xylene and ethylbenzene.[8][9][10] The ratio of isomers can be shifted to favor the highly valued p-xylene via the patented UOP-Isomar process[11] or by transalkylation of xylene with itself or trimethylbenzene. These conversions are catalyzed by zeolites.[3]
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 −47.87 °C (−54.17 °F) (m-xylene) to 13.26 °C (55.87 °F) (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 140 °C (284 °F). The density of each isomer is around 0.87 g/mL (7.3 lb/US gal; 8.7 lb/imp gal) and thus is less dense than water. The odor of xylene is detectable at concentrations as low as 0.08 to 3.7 ppm (parts of xylene per million parts of air) and can be tasted in water at 0.53 to 1.8 ppm.[9]
Xylene isomers | ||||
---|---|---|---|---|
General | ||||
Common name | Xylenes (mixture) |
o-Xylene | m-Xylene | p-Xylene |
Systematic name
|
Dimethylbenzene | 1,2-Dimethylbenzene | 1,3-Dimethylbenzene | 1,4-Dimethylbenzene |
Other names | Xylol | o-Xylol; Orthoxylene |
m-Xylol; Metaxylene |
p-Xylol; Paraxylene |
Molecular formula | C8H10 | |||
SMILES
|
Cc1c(C)cccc1 | Cc1cc(C)ccc1 | Cc1ccc(C)cc1 | |
Molar mass | 106.16 g/mol | |||
Appearance | Clear, colorless liquid | |||
CAS number
|
[1330-20-7] | [95-47-6] | [108-38-3] | [106-42-3] |
Properties | ||||
Density and phase | 0.864 g/mL, liquid | 0.88 g/mL, liquid | 0.86 g/mL, liquid | 0.86 g/mL, liquid |
Solubility in water
|
Practically insoluble | |||
Soluble in non-polar solvents such as aromatic hydrocarbons
| ||||
Melting point | −47.4 °C (−53.3 °F; 226 K) | −25 °C (−13 °F; 248 K) | −48 °C (−54 °F; 225 K) | 13 °C (55 °F; 286 K) |
Boiling point | 138.5 °C (281.3 °F; 412 K) | 144 °C (291 °F; 417 K) | 139 °C (282 °F; 412 K) | 138 °C (280 °F; 411 K) |
Viscosity | 0.812 cP at 20 °C (68 °F) | 0.62 cP at 20 °C (68 °F) | 0.34 cP at 30 °C (86 °F) | |
Hazards | ||||
SDS | Xylenes | o-Xylene | m-Xylene | p-Xylene |
EU pictograms |
| |||
NFPA 704 | ||||
Flash point | 30 °C (86 °F) | 17 °C (63 °F) | 25 °C (77 °F) | 25 °C (77 °F) |
H & P phrases | H225, H226, H304, H312, H315, H319, H332, H335, H412 P210, P233, P240, P241, P242, P243, P261, P264, P271, P273, P280, P301+P310, P302+P352, P303+P361+P353, P304+P312, P304+P340, P305+P351+P338, P312, P321, P322, P331, P332+P313, P337+P313, P362, P363, P370+P378, P403+P233, P403+P235, P405, P501 | |||
RTECS number
|
ZE2450000 | ZE2275000 | ZE2625000 | |
Related compounds | ||||
Related aromatic hydrocarbons |
Toluene, mesitylene, benzene, ethylbenzene | |||
Related compounds | Xylenols – types of phenols | |||
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox disclaimer and references |
Xylenes form azeotropes with water and a variety of alcohols. The azeotrope with water consists of 60% xylenes and boils at 94.5 °C.[3] As with many alkylbenzene compounds, xylenes form complexes with various halocarbons.[12] The complexes of different isomers often have dramatically different properties from each other.[13]
Applications
p-Xylene is the principal precursor to terephthalic acid and dimethyl terephthalate, both monomers used in the production of polyethylene terephthalate (PET) plastic bottles and polyester clothing. 98% of p-xylene production, and half of all xylenes produced is consumed in this manner.[10][14] 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
Laboratory use
Xylene is used in the laboratory to make baths with dry ice to cool reaction vessels,
Precursor to other compounds
In one large-scale application, para-xylene is converted to
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
Health and safety
Xylene is flammable but of modest acute toxicity, with LD50 ranges from 200 to 5000 mg/kg for animals. Oral LD50 for rats is 4300 mg/kg. The principal mechanism of detoxification is oxidation to methylbenzoic acid and hydroxylation to hydroxylene.[3]
The main effect of inhaling xylene vapor is
The side effects of exposure to low concentrations of xylene (< 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.[22][clarification needed] 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.[20]
Hearing disorders have been also linked to xylene exposure, both from studies with experimental animals,[23][24] as well as clinical studies.[25][26][27]
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.[20]
Xylenes are metabolized to methylhippuric acids.[28][29] The presence of methylhippuric acid can be used as a biomarker to determine exposure to xylene.[29][30]
See also
References
- Perseus Project.
- ^ Harper, Douglas. "xylene". Online Etymology Dictionary.
- ^ ISBN 978-3527306732.
- ISBN 0471238961.
- .
- ^ Cahours, Auguste (1850) "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).
- ^ Martindale, David C. and Kuchar, Paul J., 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.
- ^ "Xylene (Mixed Isomers), Air Toxic Hazard Summary". United States Environmental Protection Agency. Retrieved 8 February 2015.
- ^ PMID 21180450.
- ^ a b Xylene (Archived August 11, 2011, at the Wayback Machine), Swedish Chemicals Agency, apps.kemi.se, 2010. Accessed 2012-4-28.
- ^ "Capturing Opportunities for Para-xylene Production". UOP, A Honeywell Company. Retrieved 8 February 2015.
- .
- .
- ^ ICIS, Paraxylene-Orthoxylene | Prices, News & Market Analysis, icis.com, 2012. Accessed 2012-04-28.
- ^ Bostik, Safety Data Sheet Blu-Tack (Archived September 11, 2011, at the Wayback Machine), No. 13135, Bostik Corp., June 2007. Accessed 2012-04-28.
- ^ Samet, Wendy, (comp.), Appendix I, Painting Conservation Catalog, American Institute for Conservation of Historic and Artistic Works, conservation-wiki.com, September 1997. Accessed 2012-04-28.
- ^ "Cooling baths". UC Davis Chem Wiki. 2013-10-02. Archived from the original on 2015-02-08. Retrieved 8 February 2015.
- ^ Cargille, John (1985) [1964], "Immersion Oil and the Microscope", New York Microscopical Society Yearbook, archived from the original on 2011-09-11, retrieved 2011-03-10
- ISBN 9780891895817.
- ^ PMID 21180450.
- ^ "ACUTE TOXICITY SUMMARY: XYLENES" (PDF). Archived from the original (PDF) on October 22, 2015.
- ^ "Xylenes (EHC 190, 1997)".
- PMID 11484912.
- PMID 17210216.
- S2CID 45206975.
- (PDF) from the original on 2017-08-09.
- PMID 23169198.
- ^ "HIPPURIC and METHYL HIPPURIC ACIDS in urine" (PDF). NIOSH Manual of Analytical Methods (NMAM) (Fourth ed.).
- ^ S2CID 21534640.
- PMID 588486.
External links
- Chisholm, Hugh, ed. (1911). . Encyclopædia Britannica (11th ed.). Cambridge University Press.
- NIOSH Pocket Guide to Chemical Hazards (o-Xylene)
- NIOSH Pocket Guide to Chemical Hazards (m-Xylene)
- NIOSH Pocket Guide to Chemical Hazards (p-Xylene)
- Xylene, Hazard Summary (EPA) (Mixed Isomers)
- The Ear Poisons, The Synergist, American Industrial Hygiene Association, November, 2018