The term xylene or xylol refers to a mixture of three aromatic hydrocarbon isomers closely related to benzene. Xylene is a clear, colorless, sweet-smelling liquid that is very flammable. It is usually refined from crude oil in a process called alkylation. It is also produced as a by-product from coal carbonisation derived from coke ovens, extracted from crude benzole from gas, or by dehydrocyclodimerization and methylating of toluene and benzene. It is also manufactured from reformate.
- Xylene is often 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 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 xylene, is used for polymer production.
- It is used as a cleaning agent for steel and for silicon wafers and chips
- It is used as 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 gasoline and airplane fuel.
- 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 histology, xylene is also used for clearing the tissues following dehydration in preparation for paraffin wax infiltration. It is also used after sections have been stained to make them hydrophobic so that a coverslip may be applied with a resin in solvent.
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, of which 30 million tons are made annually as a precursor for polyethylene terephthalate (PET).