m-Xylene

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m-Xylene
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UN number 1307
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Template:Longitem C8H10
Molar mass 106.16 g/mol
Appearance Colorless liquid
Odor Aromatic in high concentrations
Density 0.86 g/mL
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Solubility in ethanol miscible
Solubility in diethyl ether miscible
Vapor pressure 9 mmHg (20 °C)[2]
Template:Longitem −76.56·10−6 cm3/mol
Template:Longitem 1.49722
Viscosity 0.8059 cP at 0 °C
0.6200 cP at 20 °C
Template:Longitem 0.33–0.37 D[3]
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Explosive limits 1.1%-7.0%[2]
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toluene
o-xylene
p-xylene

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m-Xylene (meta-xylene) is an aromatic hydrocarbon. It is one of the three isomers of dimethylbenzene known collectively as xylenes. The m- stands for meta-, indicating that the two methyl groups in m-xylene occupy positions 1 and 3 on a benzene ring. It is in the positions of the two methyl groups, their arene substitution pattern, that it differs from the other isomers, o-xylene and p-xylene. All have the same chemical formula C6H4(CH3)2. All xylene isomers are colorless and highly flammable.[6]

Production and use

Petroleum contains about 1 weight percent xylenes.[7] The meta isomer can be isolated from a mix of xylenes by the partial sulfonation (to which other isomers are less prone) followed by removal of unsulfonated oils and steam distillation of the sulfonated product.

The major use of meta-xylene is in the production of isophthalic acid, which is used as a copolymerizing monomer to alter the properties of polyethylene terephthalate. The conversion m-xylene to isophthalic acid entails catalytic oxidation. meta-Xylene is also used as a raw material in the manufacture of 2,4- and 2,6-xylidine as well as a range of smaller-volume chemicals.[8][6] Ammoxidation gives isophthalonitrile.

Toxicity and exposure

Xylenes are not acutely toxic, for example the LD50 (rat, oral) is 4300 mg/kg. Effects vary with animal and xylene isomer. Concerns with xylenes focus on narcotic effects.[6]

See also

References

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  3. DeanHandb, Lange´s Handbook of chemistry, 15th edition, 1999.
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  7. EPA-454/R-93-048 Locating and estimating air emissions from sources of xylene Emission Inventory Branch Technical Support Division Office of Air Quality Planning and Standards U.S. Environmental Protection Agency March 1994
  8. Ashford's Dictionary of Industrial Chemicals, third edition, page 9692.

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