Phenyl Acetate – Aromatic Ester CAS 122-79-2

Phenyl Acetate: Structure, Properties, and Applications

1. Introduction

Esters of organic acids are widely used in industry and everyday life. They can possess pleasant odors, serve as flavorings, solvents, and starting materials in various chemical processes. One such ester is phenyl acetate (also known as phenyl ethanoate, phenol acetate, or acetyloxybenzene), which is derived from acetic acid and phenol. In industry, phenyl acetate is valued for its ability to dissolve certain polymers and form stable aromatic compositions. In consumer products, it appears in perfumes and some food flavorings.

2. Chemical Structure and Nomenclature

Phenyl acetate is an ester in which a phenyl group (C₆H₅–) is linked to an acetyl moiety (CH₃C(O)–) through an oxygen atom. The structural formula is:

Ph–O–CO–CH₃

where:

• Ph (phenyl group) = C₆H₅–

• O = the central oxygen atom of the ester linkage

• CO = the carbonyl group

• CH₃ = the methyl fragment from acetic acid

IUPAC name: Phenyl acetate

Molecular formula: C₈H₈O₂

Molecular weight: 136.15 g/mol

CAS number: 122-79-2

Other synonyms: Acetic acid phenyl ester, phenol acetate, acetylphenol, acetoxybenzene

3. Physicochemical Properties

Appearance and odor: Phenyl acetate is a colorless to pale yellow liquid at room temperature with a pleasant, floral, slightly sweet odor reminiscent of jasmine and honey. Some sources describe the odor as "plastic-like".

Boiling point: 195–196°C at atmospheric pressure

Melting point: –30°C

Density: 1.07–1.073 g/mL at 25°C

Refractive index: 1.501–1.503 (nD20)

Flash point: 76–80°C (closed cup)

Vapor density: 4.7 (air = 1)

Solubility: Practically insoluble in water; miscible with alcohol, chloroform, and ether; soluble in glacial acetic acid.

Partition coefficient (log Pow): 1.49

Chemical stability: Phenyl acetate is stable at moderate temperatures and in acidic environments. It undergoes hydrolysis at elevated temperatures or in the presence of strong bases, breaking down into phenol and acetic acid (or their salts). It can also undergo the Fries rearrangement to form a mixture of o- and p-hydroxyacetophenones.

4. Synthesis Methods

Classical method – reaction of phenol with acetyl chloride or acetic anhydride: Phenyl acetate is typically produced by reacting phenol with acetic anhydride or acetyl chloride. The reaction with acetic anhydride is more environmentally friendly and less corrosive. The simplified equation is:

C₆H₅OH + (CH₃CO)₂O → C₆H₅OCOCH₃ + CH₃COOH

Direct esterification of phenol with acetic acid: This method uses phenol and acetic acid at elevated temperatures in the presence of strong acid catalysts (H₂SO₄, p-toluenesulfonic acid). However, the yield is lower than with anhydrides or acyl chlorides.

Transesterification: Phenyl acetate can also be obtained by transesterification of other acetates (e.g., methyl or ethyl acetate) with phenol under harsh conditions, though this method has limited industrial significance.

5. Applications

Perfumery and cosmetics: Phenyl acetate is valued for its soft floral-honey aroma. It is used in fragrance compositions, perfumes, lotions, and soaps, imparting notes of jasmine, honey, and green tea.

Food industry: As a flavoring agent, phenyl acetate is used in some food essences, imparting a sweet, floral note to products such as confectionery. It occurs naturally in strawberries, passion fruit, and black tea. The Joint FAO/WHO Expert Committee on Food Additives (JECFA) has concluded that phenyl acetate is of no safety concern at current levels of intake when used as a flavoring agent.

Organic synthesis: Phenyl acetate serves as a starting material or intermediate in the synthesis of various organic compounds, including pharmaceuticals. It undergoes the Fries rearrangement to form o- and p-hydroxyacetophenones, which are useful intermediates in pharmaceutical manufacture. It is also a metabolite of phenylbutyrate, used in the treatment of neuroblastoma and lung cancer. Additionally, it is used to produce acetophenone, which is employed in pharmaceuticals for treating liver diseases.

Solvent: Due to its moderate polarity and ability to dissolve certain polymers (e.g., cellulose esters), phenyl acetate is sometimes used as a solvent or co-solvent in varnishes, paints, and coating compositions.

Aromatic chemistry: Modification of the phenyl ring or subsequent substitution of the acetate group allows the production of a wide range of esters and phenolic derivatives for fragrance mixtures, drug synthesis, and other applications.

6. Toxicology and Environmental Aspects

Toxicity: Phenyl acetate is considered moderately toxic. Acute oral LD₅₀ in rats is approximately 1630–1749 mg/kg. Acute dermal LD₅₀ in rabbits is 8584 mg/kg. Inhalation of high vapor concentrations may cause respiratory and mucous membrane irritation. Skin contact may cause mild irritation. It is classified as Acute Oral Toxicity Category 4 (H302).

Flammability: Phenyl acetate is a flammable liquid. It should be kept away from heat, sparks, and open flames.

Allergenic potential: As a component of perfume compositions, it may cause individual allergic reactions in some people, especially with prolonged contact.

Environmental impact: Biodegradation of phenyl acetate in natural conditions is possible (aromatic rings can be broken down by microorganisms), but the oxidation process may take a considerable amount of time. When incinerating phenyl acetate, the risk of carbon monoxide and other harmful compounds should be considered; flue gas cleaning systems are required.

Regulatory status: Phenyl acetate is approved for use as a flavoring agent with no safety concerns at current intake levels. In the workplace, appropriate safety measures (gloves, safety goggles, ventilation) are recommended.

7. Research and Development Prospects

Derivative synthesis: Modification of phenyl acetate (e.g., by introducing substituents into the ring or changing the ester group) opens the way to new flavorings and functional materials for the perfumery, cosmetic, and pharmaceutical-chemical industries.

Catalysis and selectivity: Research is ongoing into catalysts and optimization of synthesis conditions to produce phenyl acetate with fewer by-products and higher yields, including the use of green chemistry approaches (economical use of reagents, waste reduction, use of biocatalysts).

8. Conclusion

Phenyl acetate is a versatile and valuable compound in various industries:

• Its pleasant aroma makes it sought after in perfumery, cosmetics, and food flavorings.

• Its moderate solvent properties allow its use in varnishes, paints, and polymer coatings.

• As an intermediate in organic synthesis, it is suitable for producing phenol derivatives and pharmaceutical compounds.

However, safety precautions must be observed when working with phenyl acetate due to its potential toxicity and flammability. Future research will focus on improving synthesis methods with emphasis on environmental and economic efficiency, as well as developing a wider range of derivatives with desired sensory or functional properties.