O-Xylene

o-Xylene (ortho-xylene) is an aromatic hydrocarbon with the formula C₆H₄(CH₃)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. o-Xylene is a colourless slightly oily flammable liquid.^[7]

o-Xylene

Skeletal formula Space-filling model
Names
Preferred IUPAC name 1,2-Xylene[1]
Systematic IUPAC name 1,2-Dimethylbenzene[1]
Other names o-Xylene,[1] o-Xylol
Identifiers
CAS Number	95-47-6 Y
3D model (JSmol)	Interactive image
Beilstein Reference	1815558
ChEBI	CHEBI:28063 Y
ChEMBL	ChEMBL45005 Y
ChemSpider	6967 Y
DrugBank	DB03029 Y
ECHA InfoCard	100.002.203
EC Number	202-422-2
Gmelin Reference	67796
KEGG	C07212 Y
PubChem CID	7237
RTECS number	ZE2450000
UNII	Z2474E14QP Y
UN number	1307
CompTox Dashboard (EPA)	DTXSID3021807
InChI InChI=1S/C8H10/c1-7-5-3-4-6-8(7)2/h3-6H,1-2H3 Y Key: CTQNGGLPUBDAKN-UHFFFAOYSA-N Y InChI=1/C8H10/c1-7-5-3-4-6-8(7)2/h3-6H,1-2H3 Key: CTQNGGLPUBDAKN-UHFFFAOYAE
SMILES CC1=C(C)C=CC=C1
Properties
Chemical formula	C8H10
Molar mass	106.168 g·mol−1
Appearance	Colorless liquid
Density	0.88 g/ml
Melting point	−24 °C (−11 °F; 249 K)
Boiling point	144.4 °C (291.9 °F; 417.5 K)
Solubility in water	0.02% (20 °C)[2]
Solubility in ethanol	very soluble
Solubility in diethyl ether	very soluble
Vapor pressure	7 mmHg (20°C)[2]
Magnetic susceptibility (χ)	−77.78·10−6 cm3/mol
Refractive index (nD)	1.50545
Viscosity	1.1049 cP at 0 °C 0.8102 cP at 20 °C
Structure
Dipole moment	0.64 D[3]
Hazards
Occupational safety and health (OHS/OSH):
Main hazards	Mildly toxic
GHS labelling:
Pictograms
Signal word	Danger
Hazard statements	H225, H226, H304, H305, H312, H315, H319, H332, H335, H412
Precautionary statements	P210, P233, P240, P241, P242, P243, P261, P264, P271, P273, P280, P301+P310, P302+P352, P303+P361+P353, P304+P312, P304+P340, P305+P351+P338, P312, P321, P322, P331, P332+P313, P337+P313, P362, P363, P370+P378, P403+P233, P403+P235, P405, P501
NFPA 704 (fire diamond)	2 3 0
Flash point	32 °C (90 °F; 305 K)
Autoignition temperature	463 °C (865 °F; 736 K)[4]
Explosive limits	0.9%-6.7%[2]
Threshold limit value (TLV)	100 ppm[4] (TWA), 150 ppm[4] (STEL)
Lethal dose or concentration (LD, LC):
LD50 (median dose)	4300 mg/kg (rats, orally)[5]
LCLo (lowest published)	6125 ppm (rat, 12 hr) 6125 ppm (human, 12 hr)[6]
NIOSH (US health exposure limits):
PEL (Permissible)	TWA 100 ppm (435 mg/m3)[2]
REL (Recommended)	TWA 100 ppm (435 mg/m3) ST 150 ppm (655 mg/m3)[2]
IDLH (Immediate danger)	900 ppm[2]
Safety data sheet (SDS)	External MSDS
Related compounds
Related aromatic hydrocarbons	m-xylene p-xylene toluene
Supplementary data page
O-Xylene (data page)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Y verify (what is YN ?) Infobox references

Production and use

Petroleum contains about one weight percent xylenes. Most o-xylene is produced by cracking petroleum, which affords a distribution of aromatic compounds, including xylene isomers. m-Xylene is isomerized to o-xylene. Net production was approximately 500,000 tons in the year 2000.

o-Xylene is largely used in the production of phthalic anhydride, which is a precursor to many materials, drugs, and other chemicals.^[7] Related to their easy oxidation, the methyl groups are susceptible to halogenation. When treated with elemental bromine, these groups are brominated, yielding xylylene dibromide:^[8]

C₆H₄(CH₃)₂ + 2 Br₂ → C₆H₄(CH₂Br)₂ + 2 HBr

Toxicity and exposure

Xylenes are not acutely toxic, for example the LD₅₀ (rat, oral) is 4300 mg/kg. Effects vary with animal and xylene isomer. Concerns with xylenes focus on narcotic effects.^[7]