:Styrene oxide
{{short description|Chemical compound}}
{{chembox
| Verifiedfields = changed
| Watchedfields = changed
| verifiedrevid = 433348661
| ImageFile = Styrene oxide.svg
| PIN = Phenyloxirane
| OtherNames = Epoxystyrene; Styryl oxide; Phenylethylene oxide
|Section1={{Chembox Identifiers
| CASNo_Ref = {{cascite|correct|CAS}}
| CASNo = 96-09-3
| Beilstein = 108582
| EC_number = 202-476-7
| Gmelin = 50213
| UNII_Ref = {{fdacite|correct|FDA}}
| UNII = 9QH06NGT6O
| PubChem = 7276
| RTECS = CZ9625000
| UNNumber = 2810 3082
| KEGG_Ref = {{keggcite|correct|kegg}}
| KEGG = C02083
| ChEBI_Ref = {{ebicite|changed|EBI}}
| ChEBI = 17907
| ChemSpiderID = 7005
| StdInChI = 1S/C8H8O/c1-2-4-7(5-3-1)8-6-9-8/h1-5,8H,6H2
| StdInChIKey = AWMVMTVKBNGEAK-UHFFFAOYSA-N
| SMILES = c1ccccc1C2CO2}}
|Section2={{Chembox Properties
| C=8 | H=8 | O=1
| Appearance = Colorless to light yellow liquid
| Density = 1.052 g/mL
| MeltingPtC = -37
| BoilingPtC = 194
| Solubility = }}
|Section3={{Chembox Hazards
| GHSPictograms = {{GHS07}}{{GHS08}}
| GHSSignalWord = Danger
| HPhrases = {{H-phrases|312|319|350}}
| PPhrases = {{P-phrases|201|202|264|280|281|302+352|305+351+338|308+313|312|322|337+313|363|405|501}}
| ExternalSDS = [http://msds.chem.ox.ac.uk/ST/styrene_oxide.html Oxford University MSDS]
| FlashPt =
| AutoignitionPt = }}
}}
Styrene oxide is an epoxide derived from styrene. It can be prepared by epoxidation of styrene with peroxybenzoic acid, in the Prilezhaev reaction:{{OrgSynth | author = Harold Hibbert and Pauline Burt | title = Styrene Oxide | collvol = 1 | collvolpages = 494 | year = 1941 | prep = cv1p0494}}
Styrene oxide is slightly soluble in water. A trace amount of acid in water causes hydrolysis to racemic phenylethyleneglycol via a benzylic cation. If the amount of water is not sufficient, acid-catalyzed isomerization for phenylacetaldehyde will occur.[http://www.patent-de.com/19870702/DE3546372A1.html Verfahren zur Herstellung von Phenylacetaldehyde, BASF-Patent DE3546372A1 vom 2. Juli 1987]
Styrene oxide in the body is metabolized to mandelic acid, phenylglyoxylic acid, benzoic acid and hippuric acid.
Hydrogenation of styrene oxide affords phenethyl alcohol.{{cite encyclopedia|doi = 10.1002/14356007.a11_141|chapter = Flavors and Fragrances|title = Ullmann's Encyclopedia of Industrial Chemistry|year = 2003|last1 = Fahlbusch|first1 = Karl-Georg|last2 = Hammerschmidt|first2 = Franz-Josef|last3 = Panten|first3 = Johannes|last4 = Pickenhagen|first4 = Wilhelm|last5 = Schatkowski|first5 = Dietmar|last6 = Bauer|first6 = Kurt|last7 = Garbe|first7 = Dorothea|last8 = Surburg|first8 = Horst|isbn = 978-3-527-30673-2}}
Stereospecific reactions
Since styrene oxide has a chiral center at the benzylic carbon atom, there are (R)-styrene oxide and (S)-styrene oxide. If optically pure reagent is used, only one optically pure compound will be obtained.
Toxicology
Styrene oxide is a main metabolite of styrene in humans or animals, resulting from oxidation by cytochrome P450. It is considered possibly carcinogenic from gavaging significant amounts into mice and rats.[http://www.epa.gov/ttn/atw/hlthef/styreneo.html EPA Styrene Oxide evaluation] Styrene oxide is subsequently hydrolyzed in vivo to styrene glycol by epoxide hydrolase.{{cite journal | doi = 10.2307/3428333 | author = Kenneth C. Liebman | journal = Environmental Health Perspectives | volume = 11 | pages = 115–119 | year = 1975 | url = http://ehis.niehs.nih.gov/members/1975/011/11018.PDF | title = Metabolism and toxicity of styrene | jstor = 3428333 | pmid = 809262 | pmc = 1475194 }}{{Dead link|date=June 2018 |bot=InternetArchiveBot |fix-attempted=no }}
Styrene oxide has a chiral center and thus two enantiomers. It has been reported that the two enantiomers had different toxicokinetics and toxicity{{Citation needed|date=February 2010}}. It was reported that the (R)-styrene oxide was preferentially formed in mice, especially in the lung, whereas the (S)-styrene oxide was preferentially generated in rats. In human volunteers, the cumulative excretion of the (S)-enantiomer of styrene glycol and mandelic acid were higher than the R form after exposure to styrene. In human liver microsomes, cytochrome P450-mediated styrene oxidation showed the production of more S enantiomer relative to the R enantiomer. It was also found that (S)-styrene oxide was preferentially hydrolyzed than the R enantiomer in human liver microsomes. Animal studies have shown that the (R)-enantiomer of styrene oxide was more toxic than the (S)-enantiomer in mice.