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Para-xylene

p-xylene - schematic representation
Skeletal formula
Space-filling model
Space-filling model
Names
Preferred IUPAC name
1,4-Xylene
Systematic IUPAC name
1,4-Dimethylbenzene
Other names
p-Xylene
Identifiers
106-42-3 YesY
3D model (Jmol) Interactive image
ChEBI CHEBI:27417 N
ChEMBL ChEMBL31561 N
ChemSpider 7521 N
ECHA InfoCard 100.003.088
KEGG C06756 YesY
PubChem 7809
RTECS number ZE2625000
UNII 6WAC1O477V N
Properties
C8H10
Molar mass 106.17 g·mol−1
Appearance Colorless liquid
Odor Aromatic
Density 0.861 g/mL
Melting point 13.2 °C (55.8 °F; 286.3 K)
Boiling point 138.35 °C (281.03 °F; 411.50 K)
Insoluble
Solubility in ethanol Very soluble
Solubility in diethyl ether Very soluble
Vapor pressure 9 mmHg (20°C)
-76.78·10−6 cm3/mol
1.49582
Viscosity 0.7385 cP at 0 °C
0.6475 cP at 20 °C
0.00 D
Hazards
Main hazards Harmful or fatal if swallowed. Vapor harmful. Flammable liquid and vapor.
Safety data sheet See: data page
External MSDS
R-phrases R10 R20 R21 R36 R38
S-phrases S25
NFPA 704
Flammability code 3: Liquids and solids that can be ignited under almost all ambient temperature conditions. Flash point between 23 and 38 °C (73 and 100 °F). E.g., gasoline) Health code 2: Intense or continued but not chronic exposure could cause temporary incapacitation or possible residual injury. E.g., chloroform Reactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g., liquid nitrogen Special hazards (white): no codeNFPA 704 four-colored diamond
Flash point 27 °C (81 °F; 300 K)
528 °C (982 °F; 801 K)
Explosive limits 1.1%-7.0%
100 ppm (TWA), 150 ppm (STEL)
Lethal dose or concentration (LD, LC):
4550 ppm (rat, 4 hr)
3401 ppm (mouse)
US health exposure limits (NIOSH):
PEL (Permissible)
TWA 100 ppm (435 mg/m3)
REL (Recommended)
TWA 100 ppm (435 mg/m3) ST 150 ppm (655 mg/m3)
IDLH (Immediate danger)
900 ppm
Related compounds
benzene
toluene
o-xylene
m-xylene
Supplementary data page
Refractive index (n),
Dielectric constantr), etc.
Thermodynamic
data
Phase behaviour
solid–liquid–gas
UV, IR, NMR, MS
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N  (what is YesYN ?)
Infobox references

p-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, as illustrated here in the schematic representation. It is in the positions of the two methyl groups, their arene substitution pattern, that it differs from the other isomers, o-xylene and m-xylene. Each of the three isomers has two methyl substituents attached to the benzene ring; ignoring the substitution patterns they therefore all have the same chemical formula C6H4(CH3)2. Like all xylene isomers, p-xylene is dangerously flammable.

For historical reasons, various sources refer to p-xylene as any of: 1,4-dimethylbenzene, p-dimethylbenzene; p-xylol; 1,4-xylene; p-methyltoluene; para-sylene; chromar; scintillar; 4-methyltoluene; NSC 72419; or 1,4-dimethyl-benzene. According to convenience, the chemical formula may be represented as C8H10 or C6H4(CH3)2.

p-Xylene is a colorless, flammable liquid practically insoluble in water. The boiling point is 138.35 °C (281 °F) and the melting point 13.2 °C (56 °F). Its specific gravity is 0.86.
p-Xylene is highly flammable, with a flash point of 27°C.
The odor threshold of p-xylene is 0.62 parts per million (ppm).

The production of p-xylene is industrially significant world-wide, with annual demand estimated at 37 million tons in 2014, and still on the increase.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.


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