p-Xylene

p-Xylene is an aromatic hydrocarbon based on benzene with two methyl substituents with the chemical formula C8H10 or C6H4(CH3)2. The “p” stands for para, identifying the location of the methyl groups as across from one another. It is an isomer of xylene. Other isomers include o-xylene and m-xylene. The boiling point of p-xylene is 138.35 °C (281 °F) and the melting point is 13.2 °C (56 °F). p-Xylene is used on a large scale for the manufacture of terephthalic acid for polyester. Its polymer is known as parylene.
p-Xylene is produced by catalytic reforming of petroleum naphtha as part of the BTX aromatics (benzene, toluene and the xylene isomers) extracted from the catalytic reformate. The p-xylene is then separated out in a series of distillation, adsorption or crystallization and reaction processes from the m-xylene, o-xylene and ethylbenzene. Its melting point is the highest among this series of isomers, but simple crystallization does not allow easy purification due to the formation of eutectic mixtures. It is also highly flammable.