Styrene
168394
216838718
2008-06-03T13:25:03Z
Rifleman 82
1255637
Reverted edits by [[Special:Contributions/Wkltan|Wkltan]] ([[User talk:Wkltan|talk]]) to last version by CrazyChemGuy
{{Chembox new
| Name = Styrene
| ImageFileL1 = Styrene.svg
| ImageSizeL1 = 120px
| ImageFileR1 = Styrene3D.png
| ImageSizeR1=120px
| ImageName = Styrene
| IUPACName = Styrene
| OtherNames = Vinyl benzene; cinnamene; styrol; ethenylbenzene; phenethylene; phenylethene; diarex HF 77; styrolene; styropol
| Section1 = {{Chembox Identifiers
| SMILES = c1ccccc1C=C
| CASNo = 100-42-5
| RTECS = WL3675000
}}
| Section2 = {{Chembox Properties
| Formula = C<sub>8</sub>H<sub>8</sub>
| MolarMass = 104.15 g/mol
| Appearance = colourless oily liquid
| Density = 0.909 g/cm³
| Solubility =< 1%
| MeltingPt = -30 °C (243.15 K)
| BoilingPt = 145 °C (418.15 K)
| Viscosity = 0.762 c[[Poise|P]] at 68 °F
| RefractIndex = 1.5469
}}
| Section3 = {{Chembox Structure
| Dipole = 0.13 [[Debye|D]]
}}
| Section7 = {{Chembox Hazards
| ExternalMSDS = [http://www.jtbaker.com/msds/englishhtml/S6986.htm MSDS]
| MainHazards = flammable, toxic
| FlashPt = 31 °C
| RSPhrases = R: 10-36 S: 38-20-23
}}
| Section8 = {{Chembox Other
| Function = styrenes
| OtherFunctn = [[Polystyrene]]<br />[[Stilbene]]
| Function = [[aromatic]] compounds
| OtherFunctn = [[Ethylbenzene]]}}
}}
'''Styrene''', also known as vinyl benzene as well as many other names (see table), is an [[organic compound]] with the [[chemical formula]] C<sub>6</sub>H<sub>5</sub>CH=CH<sub>2</sub>. Under normal conditions, this [[aromatic hydrocarbon]] is an oily [[liquid]]. It evaporates easily and has a sweet smell, although high concentrations confer a less pleasant odor. Styrene is the precursor to [[polystyrene]], an important synthetic material.
==Occurrence, history, and use==
Styrene is named after the [[styrax]] trees from whose sap ([[benzoin resin]]) it can be extracted. Low levels of styrene occur naturally in plants as well as a variety of foods such as fruits, vegetables, nuts, beverages, and meats. The production of styrene in the United States increased dramatically during the 1940s to supply the war needs for [[synthetic rubber]].
Because the styrene [[molecule]] has a [[Vinyl (molecule)|vinyl]] group with a [[double bond]], it can [[polymerize]] to give plastics such as [[polystyrene]], [[Acrylonitrile butadiene styrene|ABS]], [[styrene-butadiene]] (SBR) [[rubber]], styrene-butadiene latex, SIS (styrene-isoprene-styrene), S-EB-S (styrene-ethylene/butylene-styrene), styrene-[[divinylbenzene]] (S-DVB), and unsaturated [[polyester]]s. These materials are used in rubber, plastic, insulation, [[fiberglass]], pipes, [[automobile]] and boat parts, food containers, and carpet backing.
==Production==
Styrene is produced in industrial quantities from [[ethylbenzene]], which is in turn prepared from [[benzene]] and [[ethylene]].<ref name=Ullmann>Denis H. James William M. Castor, “Styrene” in Ullmann’s Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim, 2005.</ref>
===Dehydrogenation of ethylbenzene===
Styrene is most commonly produced by the [[catalyst|catalytic]] [[dehydrogenation]] of [[ethylbenzene]]. Ethylbenzene is mixed in the gas phase with 10–15 times its volume in high-temperature [[steam]], and passed over a solid catalyst bed. Most ethylbenzene dehydrogenation catalysts are based on [[iron(III) oxide]], promoted by several percent [[potassium oxide]] or [[potassium carbonate]]. On this catalyst, an [[endothermic]], [[reversible reaction|reversible]] [[chemical reaction]] takes place.{{Fact|date=May 2008}}
{| style="text-align: center"
|[[Image:ctk-ethylbenzene.png|Ethylbenzene]]
|[[Image:ctk-arrow-eq.png]]
|[[Image:ctk-styrene.png|Styrene]]
|[[Image:ctk-plus.png]]
|[[Image:ctk-h2.png|Hydrogen]]
|}
Steam serves several roles in this reaction. It is the source of heat for powering the endothermic reaction, and it removes coke that tends to form on the iron oxide catalyst through the [[water gas shift reaction]]. The potassium promoter enhances this decoking reaction. The steam also dilutes the reactant and products, shifting the position of [[chemical equilibrium]] towards products. A typical styrene plant consists of two or three reactors in series, which operate under vacuum to enhance the conversion and selectivity. Typical per-pass conversions are ca. 65% for two reactors and 70-75% for three reactors. Selectivity to styrene is 93-97%. The main byproducts are benzene and [[toluene]]. Because styrene and ethylbenzene have similar boiling points (145 and 136 °C, respectively), their separation requires tall distillation towers and high return/reflux ratios. At its distillation temperatures, styrene tends to polymerize. To minimize this problem, early styrene plants added elemental sulfur to inhibit the polymerization. During the 1970s, new free radical inhibitor consisting of [[phenol]]-based retarders were developed. These reagents are added prior to the distillation.
Improving conversion and so reducing the amount of ethylbenzene that must be separated is the chief impetus for researching alternative routes to styrene. Other than the [[POSM]] process, none of these routes like obtaining styrene from butadiene have been commercially demonstrated.
===Via ethylbenzenehydroperoxide===
Commercially styrene is also co-produced with propylene oxide in a process known as POSM ([[Lyondell Chemical Company]]) or SM/PO ([[Royal Dutch Shell|Shell]]) for Styrene Monomer / Propylene Oxide. In this process ethylbenzene is reacted with oxygen to form the hydroperoxide of ethylbenzene. This hydroperoxide is then used to oxidize [[propylene]] to propylene oxide. The resulting phenylethanol is dehydrated to give styrene:
:C<sub>6</sub>H<sub>5</sub>CH<sub>2</sub>CH<sub>3</sub> + O<sub>2</sub> → C<sub>6</sub>H<sub>5</sub>CH<sub>2</sub>CH<sub>2</sub>O<sub>2</sub>H
:C<sub>6</sub>H<sub>5</sub>CH<sub>2</sub>CH<sub>2</sub>O<sub>2</sub>H + CH<sub>3</sub>CH=CH<sub>2</sub> → C<sub>6</sub>H<sub>5</sub>CH<sub>2</sub>CH<sub>2</sub>OH + [[Propylene oxide|CH<sub>3</sub>CHCH<sub>2</sub>O]]
:C<sub>6</sub>H<sub>5</sub>CH<sub>2</sub>CH<sub>2</sub>OH → C<sub>6</sub>H<sub>5</sub>CH=CH<sub>2</sub> + H<sub>2</sub>O
===Laboratory synthesis===
A laboratory synthesis of styrene entails the [[decarboxylation]] of [[cinnamic acid]].<ref>{{OrgSynth | author = Abbott, T. W.; Johnson, J. R.| title = Phenylethylene (Styrene) | collvol = 1 | collvolpages = 440| year = 1941 | prep = CV1P0440}}</ref>
===Other methods===
Exelus Inc. (Livingston NJ, USA) produces styrene from toluene and methanol, at 425 °C and atmospheric pressure, by forcing these components through a proprietary zeolitic catalyst that affords a 9:1 mixture of styrene and ethylbenzene.<ref>Stephen K. Ritter, Chemical & Engineering News, 19 March 2007, p.46</ref>
==Health effects==
Styrene is only weakly toxic, with an [[LD50]] of 500-5000 mg/kg (rats).<ref name=Ullmann/>
The US Agency for Toxic Substances and Disease Registry (ATSDR) states that human exposure to high levels of styrene (more than 1000 times higher than levels normally found in the natural environment) may induce adverse nervous system effects. These health effects include changes in color vision, tiredness, feeling drunk, slowed reaction time, concentration problems, or balance problems <ref>http://www.atsdr.cdc.gov/tfacts53.pdf</ref>.
Styrene is classified as a possible human carcinogen by the [[International Agency for Research on Cancer]] (IARC).<ref name="osha">{{cite web | title=Styrene | publisher=''[[Occupational Safety and Health Administration]]'' | url=http://www.osha.gov/SLTC/styrene/index.html | accessdate=2007-12-02}}</ref> The U.S. Environmental Protection Agency (EPA) does not have a cancer classification for styrene, but is evaluating its potential carcinogenicity. The EPA has described styrene as "a suspected carcinogen" and "a suspected toxin to the gastrointestinal, kidney, and respiratory systems, among others."<ref name="epa2004">{{cite web | title=EPA settles case against Phoenix company for toxic chemical reporting violations | publisher=''U.S. Environmental Protection Agency'' | url=http://yosemite.epa.gov/opa/admpress.nsf/6427a6b7538955c585257359003f0230/09b1cf3cd5813928852570d8005e1603!OpenDocument | accessdate=2008-02-11}}</ref><ref name="epa2003">{{cite web | title=EPA Fines California Hot Tub Manufacturer for Toxic Chemical Release Reporting Violations | publisher=''U.S. Environmental Protection Agency'' | url=http://yosemite.epa.gov/opa/admpress.nsf/6427a6b7538955c585257359003f0230/b3249e555c0ed02c852570d8005e1576!OpenDocument | accessdate=2008-02-11}}</ref>
==References==
<references/>
[[Category:Aromatic hydrocarbons]]
[[Category:Hazardous air pollutants]]
[[Category:Monomers]]
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