xylene

The term xylene or xylol refers to a mixture of three aromatic hydrocarbon isomers which is used as a solvent in the printing, rubber, and leather industries. Xylene is a clear, colorless, sweet-smelling liquid that is very flammable. It is usually refined from crude oil in a process called alkylation. Like other solvents, xylene is also used as an inhalant drug for its intoxicating properties.

Chemical properties

Xylene is a generic term for a group of three aromatic hydrocarbon isomers, essentially benzene derivatives, which encompasses ortho-, meta-, and para- isomers of dimethyl benzene. The o-, m- and p- designations specify to which carbon atoms (of the 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 the p- isomer has the IUPAC name of 1,4-dimethylbenzene. Solvent grade xylene usually contains a small percentage of ethylbenzene as a contaminant.

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 for each isomer is around 140 °C (284.00 °F). The density is at around 0.87 g/mL (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.

Xylene 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 (C6H4C2H6)
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	3 2 0
Flash point	30 °C (86 °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

The xylenes, as with many alkylbenzene compounds form complexes with various halocarbons. The complexes of different isomers often have dramatically different properties from each other.^[1]

Applications

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 [1], 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. In biochemistry, xylene is also used for making slides of specimens hydrophobic in preparation for coverslip mounting.

Related compounds

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

In articles of commerce, the term xylol refers to the solvent mixture of three xylene isomers, sometimes containing ethylbenzene. In the chemical trade, this mixture is referred to as xylenes (plural). This substance must not be confused with the toxic and corrosive xyleneol compounds, which are dimethyl phenol isomers.

Health effects

Xylene exhibits neurological effects. High levels from exposure for acute (14 days or less) or chronic periods (more than 1 year) can cause headaches, lack of muscle coordination, dizziness, confusion, and changes in one's sense of balance^{[citation needed]} . 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 and other problems with the lungs, delayed reaction time, memory difficulties, stomach discomfort, and possibly adverse effects on the liver and kidneys. It can cause unconsciousness and even death at very high levels (see inhalants). Xylene or products containing Xylene should not be used indoors or around food.

Studies of unborn animals indicate that high concentrations of xylene may cause increased numbers of deaths, and delayed growth and development.^{[citation needed]} 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.

See also

• Water pollution
• Toxicity
• Gasoline
• Mesitylene

References

External links

• International Chemical Safety Card 0084 (o-Xylene)
• International Chemical Safety Card 0085 (m-Xylene)
• International Chemical Safety Card 0086 (p-Xylene)
• NIOSH Pocket Guide to Chemical Hazards (o-Xylene)
• NIOSH Pocket Guide to Chemical Hazards (m-Xylene)
• NIOSH Pocket Guide to Chemical Hazards (p-Xylene)
• European Chemicals Bureau
•  "xylene". Encyclopædia Britannica (11th ed.). 1911.