Styrene oxide
| Structural formula | ||||||||||
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| Structural formulas of the two isomeric styrene oxides: ( S ) - and ( R ) -enantiomer | ||||||||||
| General | ||||||||||
| Surname | Styrene oxide | |||||||||
| other names |
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| Molecular formula | C 8 H 8 O | |||||||||
| Brief description |
colorless liquid with an aromatic odor |
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| properties | ||||||||||
| Molar mass | 120.15 g mol −1 | |||||||||
| Physical state |
liquid |
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| density |
1.05 g cm −3 (20 ° C) |
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| Melting point |
−37 ° C |
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| boiling point |
194 ° C |
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| Vapor pressure |
40 Pa (20 ° C) |
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| solubility |
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| Refractive index |
1.5342 (20 ° C) |
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| safety instructions | ||||||||||
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| As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions . Refractive index: Na-D line , 20 ° C | ||||||||||
Styrene oxide (also [1,2-epoxyethyl] benzene, phenylethylene oxide , phenyloxirane, styrene epoxide) is a chemical organic compound that can be assigned to the group of epoxides or oxiranes . It thus belongs to the substituted saturated 3-ring heterocycles . With respect to the phenyl group, it is also a substituted aromatic. With regard to the chemical derivation of styrene , it can also be regarded as its derivative.
If “styrene oxide” is mentioned in this text or in the scientific literature without any additional name ( prefix ), then ( RS ) -styrene oxide - i.e. racemic (±) -styrene oxide - is meant.
Presentation and extraction
Styrene oxide can be produced by the addition of hypochlorous acid to styrene followed by the elimination of hydrogen chloride in the presence of alkali. Another possibility is the direct action of peracetic acid or hydrogen peroxide in an electrocyclic reaction on styrene.
The individual enantiomers can be synthesized by means of an asymmetric Jacobsen epoxidation or Shi epoxidation . These are also accessible via an enzymatic or chemical kinetic resolution.
properties
Styrene oxide is a colorless liquid. Styrene oxide reacts violently with nucleophiles (e.g. amines) and electrophiles. The high three-ring tension energy is released here.
Styrene oxide is only slightly soluble in water. Traces of acid in water cause spontaneous hydrolysis to phenylethylene glycol ; a racemic water adduct is formed via a benzyl cation intermediate. The epoxide hydrolase effects this hydrolysis in vivo .
With water, an azeotropic mixture is formed at 99.2 ° C , which contains 77.6% styrene oxide.
In the absence of sufficient amounts of water, it isomerizes to phenylacetaldehyde under acid catalysis . In solution, this isomerization can be prevented by adding a weak base such as solid sodium hydrogen carbonate . In vivo , styrene oxide isomerase (SOI) causes this isomerization.
At elevated temperatures, styrene oxide forms flammable vapor-air mixtures. The compound has a flash point below 74 ° C. The explosion range is between 1.1 vol.% As the lower explosion limit (LEL) and 22 vol.% As the upper explosion limit (UEL). The ignition temperature is 498 ° C. The substance therefore falls into temperature class T1.
Isomerism
Styrene oxide has a stereocenter on the benzylic carbon atom; H. it is chiral and there are ( R ) -styrene oxide and ( S ) -styrene oxide. Under achiral reaction conditions, the mixture of enantiomers is always formed as racemic styrene oxide. Styrene monooxygenase in bacteria forms ( S ) -styrene oxide.
toxicology
The vapors are irritating to the eyes and respiratory tract. Direct skin contact leads to moderate skin irritation. In the event of massive inhalation exposure, irritation of the airways, the formation of toxic pulmonary edema, nausea and central nervous depression can occur. In animal experiments, styrene oxide was found to be carcinogenic due to its high alkylation potential and is therefore considered to be toxic. In the body, its breakdown products phenylethylene glycol and phenylacetaldehyde are metabolized to mandelic acid , phenylglyoxylic acid , benzoic acid and hippuric acid.
use
The hydrogenation gives the 2-phenylethanol used as the odorant . The compound occurs as a starting material in a synthesis of the choleretic fenipentol . It is also a precursor to the manufacture of polymerization catalysts and inhibitors. It is also used as a substrate for checking the activity of hydrolase enzymes and for testing the effectiveness of chromatographic methods for the separation of enantiomers .
Individual evidence
- ↑ a b c d e f g h i Entry on (epoxyethyl) benzene in the GESTIS substance database of the IFA , accessed on January 8, 2018(JavaScript required) .
- ↑ a b c d e f g Entry on styrene oxide. In: Römpp Online . Georg Thieme Verlag, accessed on December 17, 2014.
- ↑ David R. Lide (Ed.): CRC Handbook of Chemistry and Physics . 90th edition. (Internet version: 2010), CRC Press / Taylor and Francis, Boca Raton, FL, Physical Constants of Organic Compounds, pp. 3-430.
- ↑ Entry on (epoxyethyl) benzene in the Classification and Labeling Inventory of the European Chemicals Agency (ECHA), accessed on February 1, 2016. Manufacturers or distributors can expand the harmonized classification and labeling .
- ^ LH Horsley: Azeotropic Data II , Advances in Chemistry Series 35, American Chemical Society, Washington DC, 1962.
- ↑ Patent DE3546372A1 : Process for the production of phenylacetaldehydes , applicant: BASF, July 2, 1987.