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Xylene is a colorless, sweet-smelling liquid that is extremely flammable. It occurs naturally in petroleum and coal tar and is formed during forest fires. It is also called Xylol, which is a mixture with Xylene in it. The chemical properties differ slightly from isomer to isomer. The melting point is between -47.87 °C (m-xylene) and 13.26 °C (p-xylene). The boiling point is for each isomer at around 140 °C. The density is at around 0.87 kg/L 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.
Chemical industries produce xylene from petroleum. It is one of the top 30 chemicals produced in the United States in terms of volume. 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 laquers 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.
With oxidizing agents, such as potassium permanganate (KMnO4), the methyl group can be oxidized to a carboxylic acid. By oxidizing both methyl groups towards the acid, o-xylene forms phthalic acid, whereas p-xylene forms terephthalic acid.