Styrene Oxide,CAS 96-09-3,Properties, Synthesis, and Applications

Styrene oxide is an organic compound with the molecular formula C8H8O and the IUPAC name phenyloxirane. It is an epoxide derived from styrene, which is a common monomer used to make polystyrene and other plastics. Styrene oxide has a chiral center at the benzylic carbon atom, so it exists as two enantiomers: ®-styrene oxide and (S)-styrene oxide. Styrene oxide belongs to the class of oxiranes, which are three-membered cyclic ethers with one oxygen atom and two carbon atoms.

Styrene oxide is a colorless to light yellow liquid with a sweet odor. It is slightly soluble in water and miscible with most organic solvents. It is unstable and reactive, and can undergo polymerization, hydrolysis, isomerization, ring-opening, and other reactions. It is also toxic and carcinogenic, and can cause irritation and sensitization to the skin, eyes, and respiratory tract.

Styrene oxide is mainly used as an intermediate in the synthesis of various chemicals, such as styrene glycol, phenethyl alcohol, phenylacetaldehyde, and other derivatives. These chemicals are further used in the production of fragrances, flavors, pharmaceuticals, pesticides, polymers, and other products. Styrene oxide can also be used as a reactive diluent in epoxy resins or as a modifier for unsaturated polyester resins.

Physical properties

Color: Colorless to light yellow
Shape: Liquid
Odor: Sweet
Density: 1.054 g/mL at 25 °C
Melting point: -37 °C
Boiling point: 194 °C
Flash point: 79 °C
Vapor pressure: 0.7 mmHg at 20 °C
Vapor density: 4.14 (air = 1)
Solubility in water: 3 g/L at 20 °C
Refractive index: 1.535 at 20 °C

Chemical properties

The following are some of the chemical properties of styrene oxide:

Stability: Styrene oxide is unstable and prone to polymerization with compounds possessing a labile hydrogen (such as acids and alcohols) in the presence of acids, bases or some salts. It is also sensitive to moisture and heat, and can decompose violently when heated above 200 °C or under UV light.
Reactivity: Styrene oxide is highly reactive and can undergo various reactions, such as hydrolysis, isomerization, ring-opening, addition, substitution, oxidation, reduction, and elimination. Some of the common reactions are:
- Hydrolysis: Styrene oxide can be hydrolyzed by water or acids to form racemic phenylethyleneglycol or phenylacetaldehyde, depending on the amount of water and the pH.
- Isomerization: Styrene oxide can be isomerized by acids or bases to form phenylacetaldehyde or phenylacetic acid.
- Ring-opening: Styrene oxide can be opened by nucleophiles (such as alcohols, amines, thiols, halides) to form various alkoxy-, amino-, thio-, or halo-substituted ethylbenzenes.
- Addition: Styrene oxide can be added by electrophiles (such as hydrogen halides, sulfuric acid) or radicals (such as bromine) to form halogenated or sulfonated ethylbenzenes.
- Substitution: Styrene oxide can be substituted by nucleophiles (such as cyanide, azide) or electrophiles (such as nitric acid) to form nitrile-, azido-, nitro-, or nitrate-substituted ethylbenzenes.
- Oxidation: Styrene oxide can be oxidized by strong oxidizing agents (such as permanganate, chromate, hydrogen peroxide) to form benzoic acid or phenylglyoxylic acid.
- Reduction: Styrene oxide can be reduced by hydrogen or hydride donors (such as sodium borohydride, lithium aluminum hydride) to form phenethyl alcohol or phenylethylamine.
- Elimination: Styrene oxide can be eliminated by bases (such as sodium hydroxide, potassium carbonate) to form styrene or vinylbenzene.
Acidity and basicity: Styrene oxide is neither acidic nor basic, but it can act as a Lewis acid or a Lewis base, depending on the reaction conditions and the reagents involved. For example, it can coordinate with Lewis bases (such as amines, phosphines) to form complexes, or it can accept electrons from Lewis acids (such as boron trifluoride, aluminum chloride) to form adducts.
Redox potential: Styrene oxide has a moderate redox potential and can be oxidized or reduced by various reagents. The standard electrode potential of styrene oxide/styrene couple is -0.62 V (vs. SHE) at 25 °C and pH 7.
Flammability and explosiveness: Styrene oxide is combustible and can form explosive mixtures with air. The lower and upper explosive limits are 1.1% and 22% (v/v), respectively. The autoignition temperature is 500 °C.

Synthesis methods

Styrene oxide can be synthesized by various methods, such as:

Epoxidation of styrene: This is the most common and industrial method for producing styrene oxide. Styrene can be epoxidized by different oxidizing agents, such as peracids (perbenzoic acid, peracetic acid, performic acid), hydrogen peroxide, oxygen, ozone, or metal oxides (molybdenum trioxide, vanadium pentoxide). The epoxidation can be catalyzed by various catalysts, such as acids, bases, metal salts, metal complexes, enzymes, or zeolites. The epoxidation can be performed in different solvents, such as chloroform, acetone, acetonitrile, or water. The epoxidation can produce either racemic or enantioselective styrene oxide, depending on the choice of oxidizing agent, catalyst, solvent, and reaction conditions.
Oxidation of ethylbenzene: This is an alternative method for producing styrene oxide. Ethylbenzene can be oxidized by oxygen or air in the presence of a cobalt catalyst to form styrene oxide and acetaldehyde. The oxidation can be performed in a gas phase or a liquid phase reactor at high temperature and pressure.
Other methods: Styrene oxide can also be synthesized by other methods, such as:
- Hydroxylation of styrene: Styrene can be hydroxylated by hydrogen peroxide in the presence of a titanium catalyst to form phenylethylene glycol, which can then be dehydrated by sulfuric acid to form styrene oxide.
- Chlorohydrination of styrene: Styrene can be chlorohydrinated by chlorine and water in the presence of an iron catalyst to form 2-chloroethylbenzene, which can then be dehydrochlorinated by sodium hydroxide to form styrene oxide.
- Bromination of ethylbenzene: Ethylbenzene can be brominated by bromine in the presence of light to form 1-bromoethylbenzene, which can then be dehydrobrominated by sodium hydroxide to form styrene oxide.

Applications and effects

Styrene oxide has various applications and effects in different fields

Organic synthesis: Styrene oxide is an important intermediate for organic synthesis and can be used to prepare various chemicals, such as:

Styrene glycol: This is the main product of the hydrolysis of styrene oxide and can be used as a solvent, a plasticizer, a surfactant, or a precursor for other chemicals.
Phenethyl alcohol: This is the main product of the hydrogenation of styrene oxide and can be used as a fragrance ingredient, a preservative, an antiseptic, or a precursor for other chemicals.
Phenylacetaldehyde: This is the main product of the isomerization of styrene oxide and can be used as a flavor ingredient, a perfume ingredient, or a precursor for other chemicals.

Chemical industry: Styrene oxide is an important raw material for the chemical industry and can be used to produce various polymers, such as:

Epoxy resins: Styrene oxide can be used as a reactive diluent or a modifier for epoxy resins, which are widely used as adhesives, coatings, composites, and electrical insulators.
Unsaturated polyester resins: Styrene oxide can be used to modify the properties of unsaturated polyester resins, which are commonly used as plastics, fiberglass, and gel coats.
Polyamides: Styrene oxide can be used to synthesize polyamides, which are synthetic polymers with high strength, toughness, and resistance to heat and chemicals.
Polyurethanes: Styrene oxide can be used to prepare polyurethanes, which are versatile polymers with various applications in foams, elastomers, coatings, and adhesives.

Pharmaceutical industry: Styrene oxide is an intermediate for the pharmaceutical industry and can be used to synthesize various drugs, such as:

Antihistamines: Styrene oxide can be used to produce antihistamines, which are drugs that block the action of histamine and relieve allergic symptoms.
Antidepressants: Styrene oxide can be used to make antidepressants, which are drugs that affect the mood and behavior by altering the levels of neurotransmitters in the brain.
Anticonvulsants: Styrene oxide can be used to create anticonvulsants, which are drugs that prevent or reduce the frequency and severity of seizures.
Analgesics: Styrene oxide can be used to generate analgesics, which are drugs that relieve pain by blocking the transmission of pain signals.

Fragrance and flavor industry: Styrene oxide is an intermediate for the fragrance and flavor industry and can be used to produce various ingredients, such as:

Phenethyl alcohol: This is a fragrance ingredient with a rose-like odor and a flavor enhancer with a honey-like taste. It is widely used in perfumes, cosmetics, foods, and beverages.
Phenylacetaldehyde: This is a fragrance ingredient with a hyacinth-like odor and a flavor enhancer with a floral taste. It is commonly used in perfumes, cosmetics, foods, and beverages.
Other derivatives: Styrene oxide can also be used to prepare other derivatives with different odors and tastes by various reactions, such as ring-opening, addition, substitution, oxidation, reduction, or elimination. These derivatives include alkoxy-, amino-, thio-, halo-, nitrile-, azido-, nitro-, nitrate-, sulfonated ethylbenzenes.

Environmental effects: Styrene oxide has negative effects on the environment and can cause harm to aquatic life and soil organisms. It is toxic to fish, algae, bacteria, fungi, earthworms, and plants. It can bioaccumulate in aquatic organisms and biomagnify in the food chain. It can also degrade into more toxic compounds in the environment.

Health effects: Styrene oxide has adverse effects on human health and can cause damage to various organs and systems. It is toxic by inhalation, ingestion, or skin contact. It can cause irritation and sensitization to the skin, eyes, and respiratory tract. It can also cause drowsiness or dizziness. It is suspected of causing genetic defects, damaging fertility or the unborn child. It is known to cause cancer.

Safety precautions

Styrene oxide is a hazardous substance that requires special precautions for handling, storage, and disposal. Some of the safety measures are:

Handling: Work under hood. Do not inhale substance/mixture. Avoid generation of vapors/aerosols. Use personal protective equipment as required. Wear protective gloves/protective clothing/eye protection/face protection. Wash hands thoroughly after handling. Do not eat, drink or smoke when using this product. Contaminated work clothing should not be allowed out of the workplace.
Storage: Store locked up. Store in a well-ventilated place. Keep container tightly closed. Keep away from heat/sparks/open flames/hot surfaces. Do not expose to light or moisture.
Disposal: Dispose of contents/container to an approved waste disposal plant. Do not release into the environment. Follow local regulations for waste disposal.