Styrene oxide is an

epoxide In organic chemistry, an epoxide is a cyclic ether () with a three-atom ring. This ring approximates an equilateral triangle, which makes it strained, and hence highly reactive, more so than other ethers. They are produced on a large scale ...

derived from

styrene Styrene () is an organic compound with the chemical formula C6H5CH=CH2. This derivative of benzene is a colorless oily liquid, although aged samples can appear yellowish. The compound evaporates easily and has a sweet smell, although high concen ...

. It can be prepared by epoxidation of

with

peroxybenzoic acid Peroxybenzoic acid is an organic compound with the formula C6H5CO3H. It is the simplest aryl peroxy acid. It may be synthesized from benzoic acid and hydrogen peroxide, or by the treatment of benzoyl peroxide with sodium methoxide, followed by ...

, in the

Prilezhaev reaction The Prilezhaev reaction, also known as the Prileschajew reaction or Prilezhaev epoxidation, is the chemical reaction of an alkene with a peroxy acid to form epoxides. It is named after Nikolai Prilezhaev, who first reported this reaction in 1909 ...

: 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. Styrene oxide in the body is metabolized to

mandelic acid Mandelic acid is an aromatic alpha hydroxy acid with the molecular formula C6H5CH(OH)CO2H. It is a white crystalline solid that is soluble in water and polar organic solvents. It is a useful precursor to various drugs. The molecule is chiral. T ...

, phenylglyoxylic acid,

benzoic acid Benzoic acid is a white (or colorless) solid organic compound with the formula , whose structure consists of a benzene ring () with a carboxyl () substituent. It is the simplest aromatic carboxylic acid. The name is derived from gum benzoin, ...

and

hippuric acid Hippuric acid ( Gr. ''hippos'', horse, ''ouron'', urine) is a carboxylic acid and organic compound. It is found in urine and is formed from the combination of benzoic acid and glycine. Levels of hippuric acid rise with the consumption of phenol ...

Hydrogenation Hydrogenation is a chemical reaction between molecular hydrogen (H2) and another compound or element, usually in the presence of a catalyst such as nickel, palladium or platinum. The process is commonly employed to reduce or saturate organ ...

of styrene oxide affords

phenethyl alcohol Phenethyl alcohol, or 2-phenylethanol, is the organic compound that consists of a phenethyl group (C6H5CH2CH2) attached to OH. It is a colourless liquid that is slightly soluble in water (2 ml/100 ml H2O), but miscible with most organic solvents. ...

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 Cytochromes P450 (CYPs) are a superfamily of enzymes containing heme as a cofactor that functions as monooxygenases. In mammals, these proteins oxidize steroids, fatty acids, and xenobiotics, and are important for the clearance of various co ...

. It is considered possibly

carcinogenic A carcinogen is any substance, radionuclide, or radiation that promotes carcinogenesis (the formation of cancer). This may be due to the ability to damage the genome or to the disruption of cellular metabolic processes. Several radioactive subs ...

from gavaging significant amounts into mice and rats. Styrene oxide is subsequently hydrolyzed ''in vivo'' to styrene glycol by

epoxide hydrolase Epoxide hydrolases (EH's), also known as epoxide hydratases, are enzymes that metabolize compounds that contain an epoxide residue; they convert this residue to two hydroxyl residues through an epoxide hydrolysis reaction to form diol products. ...

. Styrene oxide has a

chiral center In stereochemistry, a stereocenter of a molecule is an atom (center), axis or plane that is the focus of stereoisomerism; that is, when having at least three different groups bound to the stereocenter, interchanging any two different groups ...

and thus two enantiomers. It has been reported that the two enantiomers had different

toxicokinetics Toxicokinetics (often abbreviated as 'TK') is the description of both what rate a chemical will enter the body and what occurs to excrete and metabolize the compound once it is in the body. Relation to Pharmacokinetics It is an application of ph ...

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 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.

References

{{Reflist Epoxides Phenyl compounds IARC Group 2A carcinogens