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p-Xylene (para-xylene) is an aromatic hydrocarbon. It is one of the three isomers of dimethylbenzene known collectively as xylenes . The p- stands for para- , indicating that the two methyl groups in p -xylene occupy the diametrically opposite substituent positions 1 and 4.
The physical properties of the isomers of xylene differ slightly. The melting point ranges from −47.87 °C (−54.17 °F) (m-xylene) to 13.26 °C (55.87 °F) (p-xylene)—as usual, the para isomer's melting point is much higher because it packs more readily in the crystal structure. The boiling point for each isomer is around 140 °C (284 °F).
For the hydrocarbons with no further unsaturation, there are four isomers. There are three xylenes and one ethylbenzene. The substances are: ... p-xylene (1,4 ...
In the petroleum refining and petrochemical industries, the initialism BTX refers to mixtures of benzene, toluene, and the three xylene isomers, all of which are aromatic hydrocarbons. The xylene isomers are distinguished by the designations ortho – (or o –), meta – (or m –), and para – (or p –) as indicated in the adjacent diagram.
Alkylbenzene isomers can be differentiated by observing the position of alkyl substituents on the benzene ring using chemical ionization-proton exchange mass spectrometry. Conventional GC-MS yields limited results because the isomers have identical molecular weight and substituents.
Toluene disproportionation (TDP) is the conversion of toluene to benzene and xylene. [66] Given that demand for para-xylene (p-xylene) substantially exceeds demand for other xylene isomers, a refinement of the TDP process called Selective TDP (STDP) may be used. In this process, the xylene stream exiting the TDP unit is approximately 90% p ...
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In chemistry, isomers are molecules or polyatomic ions with identical molecular formula – that is, the same number of atoms of each element – but distinct arrangements of atoms in space. [1] Isomerism refers to the existence or possibility of isomers.