Xylene

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The term xylene or xylol refers to a mixture of three structural isomers of the aromatic hydrocarbon dimethylbenzene. 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.[1] It is also manufactured from reformate.

Xylene is used as a solvent in the printing, rubber, and leather industries. Xylene is also abused as an inhalant drug for its intoxicating properties.[citation needed]

Contents

Chemical properties

Xylene 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.

Some chemical and physical properties differ from isomer to isomer. The melting point ranges from −47.87 °C (−54.17 °F) (m-xylene) to 13.26 °C (55.87 °F) (p-xylene). The boiling point for each isomer is around 140 °C (284.00 °F). The density of each is 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.

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