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The C 2 benzenes are a class of organic aromatic compounds which contain a benzene ring and two other carbon atoms. For the hydrocarbons with no further unsaturation, there are four isomers. There are three xylenes and one ethylbenzene .
The boiling point for each isomer is around 140 °C (284 °F). The density of each isomer is around 0.87 g/mL (7.3 lb/US gal; 8.7 lb/imp gal) and thus is less dense than water. The odor of xylene is detectable at concentrations as low as 0.08 to 3.7 ppm (parts of xylene per million parts of air) and can be tasted in water at 0.53 to 1.8 ppm.
The m-stands for meta-, indicating that the two methyl groups in m-xylene occupy positions 1 and 3 on a benzene ring. It is in the positions of the two methyl groups, their arene substitution pattern, that it differs from the other isomers, o-xylene and p-xylene. All have the same chemical formula C 6 H 4 (CH 3) 2. All xylene isomers are ...
o-Xylene (ortho-xylene) is an aromatic hydrocarbon with the formula C 6 H 4 (CH 3) 2, with two methyl substituents bonded to adjacent carbon atoms of a benzene ring (the ortho configuration). It is a constitutional isomer of m -xylene and p -xylene , the mixture being called xylene or xylenes.
For example, the three isomers of xylene CH 3 C 6 H 4 CH 3, commonly the ortho-, meta-, and para-forms, are 1,2-dimethylbenzene, 1,3-dimethylbenzene, and 1,4-dimethylbenzene. The cyclic structures can also be treated as functional groups themselves, in which case they take the prefix "cyclo alkyl -" (e.g. "cyclohexyl-") or for benzene, "phenyl-".
1,2-Dichlorobenzene is obtained as a side-product of the production of chlorobenzene: C 6 H 5 Cl + Cl 2 → C 6 H 4 Cl 2 + HCl. The reaction also affords the 1,4- and small amounts of the 1,3-isomer. The 1,4- isomer is preferred over the 1,2- isomer due to steric hindrance.
Mesitylene or 1,3,5-trimethylbenzene is a derivative of benzene with three methyl substituents positioned symmetrically around the ring. The other two isomeric trimethylbenzenes are 1,2,4-trimethylbenzene (pseudocumene) and 1,2,3-trimethylbenzene (hemimellitene).
C 6 H 6 + C 2 H 4 → C 6 H 5 C 2 H 5. The diethylbenzene is an inadvertent side product. C 6 H 5 C 2 H 5 + C 2 H 4 → C 6 H 4 (C 2 H 5) 2. Using shape-selective zeolite catalysts, the para isomer can be produced in high selectivity. Much diethylbenzene is recycled by transalkylation to give ethylbenzene: [1] C 6 H 4 (C 2 H 5) 2 + C 6 H 6 → ...