P-xylene
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 Space-filling model
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| Names | |
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Preferred IUPAC name
1,4-Xylene
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Systematic IUPAC name
1,4-Dimethylbenzene
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| Other names
p-Xylene
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| Identifiers | |
106-42-3 
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| 3D model (Jmol) | Interactive image |
| ChEBI |
CHEBI:27417 
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| ChEMBL |
ChEMBL31561
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| ChemSpider |
7521
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| ECHA InfoCard | 100.003.088 |
| KEGG |
C06756
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| PubChem | 7809 |
| RTECS number | ZE2625000 |
| UNII |
6WAC1O477V
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| 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 | |
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Refractive index (nD)
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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 | |
| 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): | |
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LC50 (median concentration)
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4550 ppm (rat, 4 hr) |
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LCLo (lowest published)
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3401 ppm (mouse) |
| US health exposure limits (NIOSH): | |
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PEL (Permissible)
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TWA 100 ppm (435 mg/m3) |
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REL (Recommended)
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TWA 100 ppm (435 mg/m3) ST 150 ppm (655 mg/m3) |
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IDLH (Immediate danger)
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900 ppm |
| Related compounds | |
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Related aromatic
hydrocarbons |
benzene toluene o-xylene m-xylene |
| Supplementary data page | |
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Refractive index (n), Dielectric constant (εr), etc. |
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Thermodynamic
data |
Phase behaviour solid–liquid–gas |
| UV, IR, NMR, MS | |
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Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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 (what is ?) |
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| 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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Wikipedia