Styrene oxide

Styrene oxide is an epoxide derived from styrene. It can be prepared by epoxidation of styrene with peroxybenzoic acid, in the Prilezhaev reaction:[1]

Styrene oxide
Names
Preferred IUPAC name
2-Phenyloxirane
Other names
Phenyloxirane; Epoxystyrene; Styryl oxide; Phenylethylene oxide
Identifiers
3D model (JSmol)
ChEBI
ChemSpider
ECHA InfoCard 100.002.252
KEGG
UNII
Properties
C8H8O
Molar mass 120.151 g·mol−1
Appearance Colorless to light yellow liquid
Density 1.052 g/mL
Melting point −37 °C (−35 °F; 236 K)
Boiling point 194 °C (381 °F; 467 K)
Hazards
Safety data sheet Oxford University MSDS
Harmful (XN); Corrosive (C)
R-phrases (outdated) R20 R22 R34 R36 R37 R38
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N verify (what is YN ?)
Infobox references

Styrene oxide is slightly soluble in water. A trace amount of acid in water causes hydrolysis to racemic phenylethyleneglycol via aryl cation. If the amount of water is not sufficient, acid-catalyzed isomerization for phenylacetaldehyde will occur.[2]

Styrene oxide in the body is metabolized to mandelic acid, phenylglyoxylic acid, benzoic acid and hippuric acid.

Hydrogenation of styrene oxide affords phenethyl alcohol.[3]

Stereospecific reaction

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.[4] Styrene oxide is subsequently hydrolyzed in vivo to styrene glycol by epoxide hydrolase.[5]

Styrene oxide has a chiral center and thus two enantiomers. It has been reported that the two enantiomers had different toxicokinetics and toxicity. 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 mendelic 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.

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References
  1. Harold Hibbert and Pauline Burt (1941). "Styrene Oxide". Organic Syntheses.; Collective Volume, 1, p. 494
  2. Verfahren zur Herstellung von Phenylacetaldehyde, BASF-Patent DE3546372A1 vom 2. Juli 1987
  3. Fahlbusch, Karl-Georg; Hammerschmidt, Franz-Josef; Panten, Johannes; Pickenhagen, Wilhelm; Schatkowski, Dietmar; Bauer, Kurt; Garbe, Dorothea; Surburg, Horst (2003). "Flavors and Fragrances". Ullmann's Encyclopedia of Industrial Chemistry. doi:10.1002/14356007.a11_141. ISBN 978-3-527-30673-2.
  4. EPA Styrene Oxide evaluation
  5. Kenneth C. Liebman (1975). "Metabolism and toxicity of styrene" (PDF). Environmental Health Perspectives. 11: 115–119. doi:10.2307/3428333. JSTOR 3428333.
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