Styrene, also known as ethenylbenzene, vinylbenzene, and phenylethene, is an organic compound with the chemical formula C6H5CH=CH2. This derivative of benzene is a colorless oily liquid that evaporates easily and has a sweet smell, although high concentrations have a less pleasant odor. Styrene is the precursor to polystyrene and several copolymers. Approximately 25 million tonnes of styrene were produced in 2010.
|Preferred IUPAC name|
3D model (JSmol)
CompTox Dashboard (EPA)
|Molar mass||104.15 g/mol|
|Appearance||colorless oily liquid|
|Melting point||−30 °C (−22 °F; 243 K)|
|Boiling point||145 °C (293 °F; 418 K)|
|Vapor pressure||5 mmHg (20°C)|
Refractive index (nD)
|Viscosity||0.762 cP at 20 °C|
|Main hazards||flammable, toxic|
|Safety data sheet||MSDS|
|R-phrases (outdated)||R10 R36|
|S-phrases (outdated)||S38 S20 S23|
|NFPA 704 (fire diamond)|
|Flash point||31 °C (88 °F; 304 K)|
|Lethal dose or concentration (LD, LC):|
LC50 (median concentration)
|2194 ppm (mouse, 4 hr)|
5543 ppm (rat, 4 hr)
LCLo (lowest published)
|10,000 ppm (human, 30 min)|
2771 ppm (rat, 4 hr)
|NIOSH (US health exposure limits):|
|TWA 100 ppm C 200 ppm 600 ppm (5-minute maximum peak in any 3 hours)|
|TWA 50 ppm (215 mg/m3) ST 100 ppm (425 mg/m3)|
IDLH (Immediate danger)
related aromatic compounds
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Occurrence, history, and use
Styrene is named after storax balsam, the resin of Liquidambar trees of the Altingiaceae plant family. Styrene occurs naturally in small quantities in some plants and foods (cinnamon, coffee beans, and peanuts) and is also found in coal tar.
In 1839, the German apothecary Eduard Simon isolated a volatile liquid from the resin (called storax or styrax (Latin)) of the American sweetgum tree (Liquidambar styraciflua). He called the liquid "styrol" (now styrene). He also noticed that when styrol was exposed to air, light, or heat, it gradually transformed into a hard, rubber-like substance, which he called "styrol oxide". By 1845, the German chemist August Hofmann and his student John Blyth (1814–1871) had determined styrene's empirical formula: C8H8. They had also determined that Simon's "styrol oxide" — which they renamed "metastyrol" — had the same empirical formula as styrene. Furthermore, they could obtain styrene by dry-distilling "metastyrol". In 1865, the German chemist Emil Erlenmeyer found that styrene could form a dimer, and in 1866 the French chemist Marcelin Berthelot stated that "metastyrol" was a polymer of styrene (i.e. polystyrene). Meanwhile, other chemists had been investigating another component of storax, namely, cinnamic acid. They had found that cinnamic acid could be decarboxylated to form "cinnamene" (or "cinnamol"), which appeared to be styrene. In 1845, French chemist Emil Kopp suggested that the two compounds were identical, and in 1866, Erlenmeyer suggested that both "cinnamol" and styrene might be vinylbenzene. However, the styrene that was obtained from cinnamic acid seemed different from the styrene that was obtained by distilling storax resin: the latter was optically active. Eventually, in 1876, the Dutch chemist van 't Hoff resolved the ambiguity: the optical activity of the styrene that was obtained by distilling storax resin was due to a contaminant.
Industrial production from ethylbenzene
Styrene plays an important role in chemical production to make latex, synthetic rubber, and other polystyrene resins. A common way to produce styrene is through the dehydrogenation of ethylbenzene. Benzene and ethylene are first compressed and sent to a reactor to produce ethylbenzene in the presence of a Friedel–Crafts catalyst (aluminum chloride) at approximately 95 °C. The reaction occurs as
- C6H6 + CH2CH2 → C6H5CH2CH3
The product mixture is then fed into a distillation column to be separated into ethylbenzene, benzene, and polyethylbenzenes. After the partial distillation, the ethylbenzene is fed out with a high purity of over 99% at 136 °C (its boiling point). A benzene recycle stream (to the original entering benzene stream) and a mixture stream of polyethylbenzenes exit the reactor separately. The effluent mixture of polyethylbenzenes is heated via a heat exchanger and sent to a reactor at 200 °C to be dealkylated into benzene. The products, along with unreacted benzene, are then cooled via another heat exchanger and sent into the aforementioned benzene recycle stream. The fed-out ethylbenzene vapor stream is mixed with superheated steam and the resulting mixture is heated, then dehydrogenated to styrene mixture via an adiabatic reactor using an iron(III) oxide catalyst. The reactor is run with added steam, with a typical yield of 88–94%, and the reaction occurs as
- C6H5CH2CH3 → C6H5CHCH2 + H2
The exit stream is condensed and sent to a distillation column, which separates a crude styrene stream from the vent gas (hydrogen and other vapors), which exits from the top, and the liquid condensate, which exits from the column’s bottom. Via this process, the selectivity of styrene from ethylbenzene is approximately 90%. The crude styrene stream is purified via a polymerization inhibitor in a reactor.
Other industrial routes
From ethylbenzene hydroperoxide
Styrene is also co-produced commercially in a process known as POSM (Lyondell Chemical Company) or SM/PO (Shell) for styrene monomer / propylene oxide. In this process ethylbenzene is treated with oxygen to form the ethylbenzene hydroperoxide. This hydroperoxide is then used to oxidize propylene to propylene oxide. The resulting 1-phenylethanol is dehydrated to give styrene:
From toluene and methanol
Styrene can be produced from toluene and methanol, which are cheaper raw materials than those in the conventional process. This process has suffered from low selectivity associated with the competing decomposition of methanol. Exelus Inc. claims to have developed this process with commercially viable selectivities, at 400–425 °C and atmospheric pressure, by forcing these components through a proprietary zeolitic catalyst. It is reported that an approximately 9:1 mixture of styrene and ethylbenzene is obtained, with a total styrene yield of over 60%.
From benzene and ethane
Another route to styrene involves the reaction of benzene and ethane. This process is being developed by Snamprogetti and Dow. Ethane, along with ethylbenzene, is fed to a dehydrogenation reactor with a catalyst capable of simultaneously producing styrene and ethylene. The dehydrogenation effluent is cooled and separated and the ethylene stream is recycled to the alkylation unit. The process attempts to overcome previous shortcomings in earlier attempts to develop production of styrene from ethane and benzene, such as inefficient recovery of aromatics, production of high levels of heavies and tars, and inefficient separation of hydrogen and ethane. Development of the process is ongoing.
The presence of the vinyl group allows styrene to polymerize. Commercially significant products include polystyrene, ABS, styrene-butadiene (SBR) rubber, styrene-butadiene latex, SIS (styrene-isoprene-styrene), S-EB-S (styrene-ethylene/butylene-styrene), styrene-divinylbenzene (S-DVB), styrene-acrylonitrile resin (SAN), and unsaturated polyesters used in resins and thermosetting compounds. These materials are used in rubber, plastic, insulation, fiberglass, pipes, automobile and boat parts, food containers, and carpet backing.
Styrene is regarded as a "known carcinogen", especially in case of eye contact, but also in case of skin contact, of ingestion and of inhalation, according to several sources. Styrene is largely metabolized into styrene oxide in humans, resulting from oxidation by cytochrome P450. Styrene oxide is considered toxic, mutagenic, and possibly carcinogenic. Styrene oxide is subsequently hydrolyzed in vivo to styrene glycol by the enzyme epoxide hydrolase. The U.S. Environmental Protection Agency (EPA) has described styrene to be "a suspected toxin to the gastrointestinal tract, kidney, and respiratory system, among others". On 10 June 2011, the U.S. National Toxicology Program has described styrene as "reasonably anticipated to be a human carcinogen". However, a STATS author describes a review that was done on scientific literature and concluded that "The available epidemiologic evidence does not support a causal relationship between styrene exposure and any type of human cancer". Despite this claim, work has been done by Danish researchers to investigate the relationship between occupational exposure to styrene and cancer. They concluded, "The findings have to be interpreted with caution, due to the company based exposure assessment, but the possible association between exposures in the reinforced plastics industry, mainly styrene, and degenerative disorders of the nervous system and pancreatic cancer, deserves attention". In 2012 the Danish EPA concluded that the styrene data do not support a cancer concern for styrene. The U.S. EPA does not have a cancer classification for styrene, but it has been the subject of their Integrated Risk Information System (IRIS) program. The U.S. National Toxicology Program of the U.S. Department of Health and Human Services has determined that styrene is "reasonably anticipated to be a human carcinogen". Various regulatory bodies refer to styrene, in various contexts, as a possible or potential human carcinogen. The International Agency for Research on Cancer considers styrene to be "possibly carcinogenic to humans".
The neurotoxic properties of styrene have also been studied and reported effects include effects on vision and on hearing functions. Studies with experimental animals, as well as epidemiologic studies have observed a synergistic interaction with noise in causing hearing difficulties.
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