Ethylbenzene is an organic compound with the formula C6H5CH2CH3. It is a highly flammable, colorless liquid with an odor similar to that of gasoline. This monocyclic aromatic hydrocarbon is important in the petrochemical industry as an intermediate in the production of styrene, the precursor to polystyrene, a common plastic material. In 2012, more than 99% of ethylbenzene produced was consumed in the production of styrene.
Ethylbenzol; Phenylethane: alpha-Methyltoluene; EB
3D model (JSmol)
CompTox Dashboard (EPA)
|Molar mass||106.168 g·mol−1|
|Melting point||−95 °C (−139 °F; 178 K)|
|Boiling point||136 °C (277 °F; 409 K)|
|0.015 g/100 mL (20 °C)|
Refractive index (nD)
|Viscosity||0.669 cP at 20 °C|
Heat capacity (C)
|GHS signal word||Danger|
|H225, H304, H320, H332, H335, H336, H351, H360, H373, H400, H411|
|P201, P202, P210, P233, P240, P241, P242, P243, P260, P261, P264, P271, P273, P280, P281, P301+310, P303+361+353, P304+312, P304+340, P305+351+338, P308+313, P312, P314, P331, P337+313|
|Flash point||22.22 °C (72.00 °F; 295.37 K)|
|430 °C (806 °F; 703 K)|
|Lethal dose or concentration (LD, LC):|
LD50 (median dose)
LCLo (lowest published)
|4000 ppm (rat, 4 hr)|
|US health exposure limits (NIOSH):|
|TWA 100 ppm (435 mg/m3)|
|TWA 100 ppm (435 mg/m3) ST 125 ppm (545 mg/m3)|
IDLH (Immediate danger)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Occurrence and applicationsEdit
3 → C6H5CH=CH2 + H
As of May 2012, greater than 99% of all the ethylbenzene produced is used for this purpose.
Ethylbenzene is added to gasoline as an anti-knock agent, meaning it reduces engine knocking and increases the octane rating. Ethylbenzene is often found in other manufactured products, including pesticides, cellulose acetate, synthetic rubber, paints, and inks. Used in the recovery of natural gas, ethylbenzene may be injected into the ground.
6 + C
4 → C
In 2012, more than 99% of ethylbenzene was produced in this way. Thus, manufacturers of ethylbenzene are the major buyers of benzene, claiming more than half of total output.
In the 1980s a zeolite-based process using vapor phase alkylation offered a higher purity and yield. Then a liquid phase process was introduced using zeolite catalysts. This offers low benzene-to-ethylene ratios, reducing the size of the required equipment and lowering byproduct production.
The acute toxicity of ethylbenzene is low, with an LD50 of about 4 grams per kilogram of body weight. The longer term toxicity and carcinogenicity is ambiguous. Eye and throat sensitivity can occur when high level exposure to ethylbenzene in the air occurs. At higher level exposure, ethylbenzene can cause dizziness. Once inside the body, ethylbenzene biodegrades to 1-phenylethanol, acetophenone, phenylglyoxylic acid, mandelic acid, benzoic acid and hippuric acid. Ethylbenzene exposure can be determined by testing for the breakdown products in urine.
As of September 2007, the United States Environmental Protection Agency (EPA) determined that drinking water with a concentration of 30 parts per million (ppm) for one day or 3 ppm for ten days is not expected to have any adverse effect in children. Lifetime exposure of 0.7 ppm ethylbenzene is not expected to have any adverse effect either. The U.S. Occupational Safety and Health Administration (OSHA) limits exposure to workers to an average 100 ppm for an 8-hour workday, a 40-hour workweek.
Ethylbenzene is classified as a possible carcinogen by the International Agency for Research on Cancer (IARC) however, the EPA has not determined ethylbenzene to be a carcinogen. The National Toxicology Program conducted an inhalation study in rats and mice. Exposure to ethylbenzene resulted in an increased incidence of kidney and testicular tumors in male rats, and trends of increased kidney tumors in female rats, lung tumors in male mice, and liver tumors in female mice.
Ethylbenzene is found mostly as a vapor in the air since it can easily move from water and soil. A median concentration of 0.62 parts per billion (ppb) was found in urban air in 1999. A study conducted in 2012 found that in-country air the median concentration was found to be 0.01 ppb and indoors the median concentration was 1.0 ppb. It can also be released into the air through the burning of coal, gas, and oil. The use of ethylbenzene in the industry contributes to ethylbenzene vapor in the air. After about three days in the air with the help of sunlight, other chemicals break down ethylbenzene into chemicals that can be found in smog. Since it does not readily bind to soil it can also easily move into groundwater. In surface water, it breaks down when it reacts with chemicals naturally found in water. Generally, ethylbenzene is not found in drinking water, however it can be found in residential drinking water wells if the wells are near waste sites, underground fuel storage tanks that are leaking, or landfills.
As of 2012, according to the EU Dangerous Substances Directive, ethylbenzene is not classified as hazardous to the environment.
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- Rabus, R.; Widdel, F. (1995). "Anaerobic degradation of ethylbenzene and other aromatic hydrocarbons by new denitrifying bacteria". Archives of Microbiology. 163 (2): 96–103. doi:10.1007/s002030050177. PMID 7710331.
- National Toxicology Program. Toxicology and Carcinogenesis Studies of Ethylbenzene (CAS No. 100-41-4) in F344/N Rats and B6C3F1 Mice (Inhalation Studies). TR No. 466. U.S. Department of Health and Human Services, Public Health Service, National Institutes of Health, Bethesda, MD. 1999.