The preparation and use of 1,4-Dimethylbenzene

The 1,4-Dimethylbenzene, also called p-Xylene, is an aromatic hydrocarbon. It is an isomer of xylene. Other isomers include o-xylene and m-xylene. It occurs in two forms, either as colorless liquid with a characteristic aromatic odor at normal temperature, or as colorless crystalline solid below 13 °C. 1,4-Dimethylbenzene which exists in the atomatic tobacco and smoke is non-corrosive to metal. When heating to its decomposition, it decomposes to methane, hydrogen, toluene, couplet toluene and 2,6 - dimethyl anthracene.
There is a considerable amount of 1,4-Dimethylbenzenein oil xylene and coal tar xylene. As the difference of boiling point between m-xylene and 1,4-Dimethylbenzene is only 0.75 °C, it can not be separated by distillation method. The current methods in domestic and foreign research are low-temperature crystallization separation, adsorption separation and complexing separation. The yield of low-temperature crystallization separation is 60-70% which is low. But the adsorption separation has relatively high yield and purity.
It is not only used as raw material in the production of polyester fibers and resins, paints, dyes and pesticides, but also used as chromatography standard materials and solvents. On a large scale, 1,4-Dimethylbenzene is used for the manufacture of terephthalic acid for polyester. In addition, it also can be used in organic synthesis. For example: it can react with benzoyl chloride to get 2,5-dimethyl-benzophenone. This reaction needs reagents CS2 and AlCl3.