Styrene oxide
Styrene oxide, chemically known as 2-phenyloxirane, is an organic epoxide compound with the molecular formula C₈H₈O and a molecular weight of 120.15 g/mol. It is a colorless to pale straw-colored liquid with a pleasant, sweet odor and serves primarily as a reactive diluent and plasticizer in epoxy resin formulations, as well as a chemical intermediate for producing phenethyl alcohol, styrene glycol, and related derivatives used in perfumes, cosmetics, surface coatings, and textile treatments.[1][2][3] The compound, with CAS number 96-09-3, exhibits key physical properties including a boiling point of 194 °C, a melting point of -37 °C, a density of 1.05 g/mL at 20 °C, and low water solubility of 3 g/L at 20 °C, making it miscible with most organic solvents. It is typically synthesized via the epoxidation of styrene using peracids such as peroxybenzoic acid. Styrene oxide is chiral, existing as a pair of enantiomers, and its structure consists of an oxirane ring substituted with a phenyl group at the 2-position.[1][3][2][4][5] Due to its reactivity as an epoxide, styrene oxide poses health risks including severe skin and eye irritation, potential sensitization, and classification as a probable human carcinogen (IARC Group 2A) based on animal studies showing liver and forestomach tumors. It may also cause central nervous system effects, liver damage, and reproductive toxicity upon exposure. Handling requires protective equipment and ventilation to mitigate inhalation and contact hazards.[2][3][6]Chemical identity
Structure
Styrene oxide has the molecular formula \ce{C8H8O} and features a three-membered epoxide (oxirane) ring attached to a phenyl group, with the structural formula \ce{C6H5-CH(O)CH2}, where the oxygen bridges the benzylic carbon and the terminal methylene carbon.[1] The oxirane ring is characterized by highly strained bond angles of approximately 60°, far from the ideal tetrahedral angle of 109.5° for sp^3-hybridized carbons, which imparts significant ring strain and underlies its chemical reactivity.[7] In the epoxide ring, the C-O bonds measure approximately 1.43 Å and the C-C bond approximately 1.47 Å, as revealed by X-ray crystallographic analyses of oxirane and related epoxides.[8] Styrene oxide is chiral due to the stereogenic center at the benzylic carbon of the epoxide ring, existing as a pair of enantiomers: (R)-styrene oxide and (S)-styrene oxide.Nomenclature
Styrene oxide is systematically named 2-phenyloxirane according to IUPAC nomenclature, reflecting its structure as an oxirane ring substituted with a phenyl group at the 2-position.[1] The common name "styrene oxide" derives from its formation via epoxidation of styrene (ethenylbenzene), a process that adds an oxygen atom across the vinyl double bond to form the epoxide.[1] Alternative synonyms include phenyloxirane, (epoxyethyl)benzene, 1,2-epoxyethylbenzene, and phenylethylene oxide.[9] In chemical databases, styrene oxide is identified by the CAS Registry Number 96-09-3 and the EC (EINECS) number 202-476-7.[1] The compound is chiral due to the stereocenter at the carbon bearing the phenyl group, leading to distinctions in nomenclature between the racemic form (styrene oxide) and its enantiomers, such as (2R)-2-phenyloxirane or (R)-styrene oxide for the R enantiomer, and (2S)-2-phenyloxirane or (S)-styrene oxide for the S enantiomer.Physical and chemical properties
Physical properties
Styrene oxide appears as a colorless to pale yellow liquid at room temperature.[2][10] Its molecular formula is C₈H₈O, corresponding to a molecular weight of 120.15 g/mol.[2] The compound has a melting point of -37 °C and a boiling point of 194 °C at 760 mmHg.[11][12]| Property | Value | Conditions |
|---|---|---|
| Density | 1.054 g/cm³ | 25 °C |
| Refractive index | 1.535 (n₂₀ᴰ) | - |