Xylene

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]


Overview

The term xylenes refers to a group of 3 benzene derivatives which encompasses ortho-, meta-, and para- isomers of dimethyl benzene. The o-, m- and p- isomers specify to which carbon atoms (of the main benzene ring) the two methyl groups are attached. Counting the carbon atoms from one of the ring carbons bonded to a methyl group, and counting towards the second ring carbon bonded to a methyl group, the o- isomer has the IUPAC name of 1,2-dimethylbenzene. The m- isomer has the IUPAC name of 1,3-dimethylbenzene. And p- isomer has the IUPAC name of 1,4-dimethylbenzene.

The xylene isomers


It is a colorless, sweet-smelling liquid that is very flammable. It occurs naturally in petroleum and coal tar and is formed during forest fires. The chemical properties differ slightly from isomer to isomer. The melting point is between -47.87 °C (-54.17 °F) (m-xylene) and 13.26 °C (55.87 °F) (p-xylene). The boiling point is for each isomer at around 140 °C (284 °F). The density is at around 0.87 kg/L (7.26 lb/U.S. gallon or 8.72 lb/imp gallon) and thus is less dense than water. Xylene in air can be smelled at 0.08 to 3.7 parts of xylene per million parts of air (ppm) and can begin to be tasted in water at 0.53 to 1.8 ppm.

Chemical industries produce xylene from petroleum. It is one of the top 30 chemicals produced in the United States in terms of volume. Xylene is used as a solvent and in the printing, rubber, and leather industries. p-Xylene is used as a feedstock in the production of terephthalic acid, which is a monomer used in the production of polymers. It is also used as a cleaning agent for steel and for silicon wafers and chips, a pesticide [2], a thinner for paint, and in paints and varnishes. It may be substituted for toluene to thin lacquers where slower drying is desired. It is found in small amounts in airplane fuel and gasoline. In animal studies it is often swabbed on the ears of rabbits to facilitate blood flow and collection, although the area must subsequently be cleansed with alcohol to prevent inflammation.

Xylenes and Its Isomers
General
Common name Xylenes o-Xylene m-Xylene p-Xylene
Systematic name Dimethylbenzenes 1,2-Dimethylbenzene 1,3-Dimethylbenzene 1,4-Dimethylbenzene
Other names Xylols 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 (-54.4°F; 225 K) 13°C (55.4°F; 286 K)
Boiling point 138.5°C (281.3°F; 412 K) 144°C (291.2°F; 417 K) 139°C (282.2°F; 412 K) 138°C (280.4°F; 411 K)
Viscosity .812 cP at 20 °C (68 °F) .62 cP at 20 °C (68 °F) .34 cP at 30 °C (86 °F)
Hazards
MSDS Xylenes o-Xylene m-Xylene p-Xylene
EU Classification Harmful (Xn)
NFPA 704
NFPA 704.svg
3
2
0
 
Flash point 24 °C (75 °F) 17 °C (63 °F) 25 °C (77 °F) 25 °C (77 °F)
R/S statement R10, R20/21, R38: (S2), S25
RTECS number ZE2450000 ZE2275000 ZE2625000
Supplementary data page
Structure & properties n, εr, etc.
Thermodynamic data Phase behaviour
Solid, liquid, gas
Spectral data UV, IR, NMR, MS
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

Related compounds

Xylenes are a starting material for the production of other chemicals. For instance chlorination gives a xylylene dichlorides or 1,2-bis(chloromethyl)benzene (again three possible isomers). With oxidizing agents, such as potassium permanganate (KMnO4), the methyl group can be oxidized to a carboxylic acid. By oxidizing both methyl groups towards the acid, o-xylene forms phthalic acid, whereas p-xylene forms terephthalic acid.

Health effects

Xylene affects the brain. High levels from exposure for short periods (14 days or less) or long periods (more than 1 year) can cause headaches, lack of muscle coordination, dizziness, confusion, and changes in one's sense of balance. Exposure of people to high levels of xylene for short periods can also cause irritation of the skin, eyes, nose, and throat; difficulty in breathing; problems with the lungs; delayed reaction time; memory difficulties; stomach discomfort; and possibly changes in the liver and kidneys. It can cause unconsciousness and even death at very high levels (see inhalants).

Studies of unborn animals indicate that high concentrations of xylene may cause increased numbers of deaths, and delayed growth and development. In many instances, these same concentrations also cause damage to the mothers. It is not yet known whether xylene harms the unborn fetus if the mother is exposed to low levels of xylene during pregnancy.

Besides occupational exposure, the principal pathway of human contact is via soil contamination from leaking underground storage tanks containing petroleum products. Humans who come into contact with the soil or groundwater may become affected. Use of contaminated groundwater as a water supply could lead to adverse health effects.

Another common form of human exposure to xylene is in the use of certain types of pens, writing and drawing instruments, bingo dabbers and art supplies.

See also

External links


cs:Xylen da:Xylen de:Xylol it:Xilene lv:Ksilols lt:Ksilenas nl:Xyleen no:Xylen fi:Ksyleeni sv:Xylen


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