The term Xylene
refers to a group of three benzene derivatives which are used as a solvent and in the printing, rubber, and leather industries. Xylene is a colorless, sweet-smelling liquid that is very flammable. Like other solvents, xylene is also used as an inhalant drug for its intoxicating properties.
Chemical properties
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
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 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.
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 , 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.
Xylene is also used as a fixation agent for animal tissues.
Xylenes and Its Isomers
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.
Health effects
Xylene has an effect on 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. |
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