Styrene oxide

Styrene oxide

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Names
IUPAC name 2-Phenyloxirane
Other names Phenyloxirane; Epoxystyrene; Styryl oxide; Phenylethylene oxide
Identifiers
CAS Number	96-09-3 N
ChEBI	CHEBI:17907
Jmol 3D model	Interactive image
KEGG	C02083 Y
PubChem	7276
SMILES c1ccccc1C2CO2
Properties
Chemical formula	C8H8O
Molar mass	120.15 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)
Vapor pressure	{{{value}}}
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

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

Styrene oxide is slightly soluble in water. 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.

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

Stereospecific reaction

Since styrene oxide has a chiral center at the benzylic carbon atom, there are (R)-styrene oxide and (S)-styrene oxide. In addition, nucleophiles always attack the secondary carbon of the oxirane ring because of stability of the intermediate and steric hindrance. 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. Styrene oxide is subsequently hydrolyzed in vivo to styrene glycol by epoxide hydrolase.

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.