14Dimethylbenzene

1,4-Dimethylbenzene, commonly known as p-xylene, is an aromatic hydrocarbon with the formula C8H10. It consists of a benzene ring bearing two methyl substituents in the para (1,4) positions. It is one of the three xylene isomers (the others being o-xylene and m-xylene) and is typically discussed in the context of petrochemical processing and plastics manufacturing.

Production and occurrence: p-Xylene is not usually produced in pure form directly from crude oil; rather it is obtained from the mixed xylene stream generated during refining and upgrading of petroleum and other hydrocarbon feedstocks. The xylene isomer mixture, containing o-, m-, and p-xylene, is separated through distillation, crystallization, or selective adsorption techniques. Para-xylene is the primary target because it is a key feedstock for the production of terephthalic acid, a precursor to polyethylene terephthalate (PET).

Uses: The principal use of p-xylene is as a feedstock for the production of terephthalic acid, which is then oxidized to form polyesters used in PET bottles, fibers, and films. It can also be converted to dimethyl terephthalate (DMT), another monomer for PET synthesis, and serves as a solvent or intermediate in various chemical manufacturing processes.

Properties: p-Xylene is a colorless, flammable liquid at room temperature with a boiling point around 139°C. It is largely immiscible with water and soluble in many organic solvents. Like other volatile organic compounds, it poses health and safety risks if inhaled or contacted, and is typically handled under standard industrial hygiene practices to minimize exposure and ignition hazards.

See also: other xylene isomers and related aromatic hydrocarbons.