Acetophenone

Description

Acetophenone is the simplest aromatic ketone and is a clear liquid/crystal and very slightly soluble in water with a sweet pungent taste and odour resembling oranges. It is used as a polymerisation catalyst for the manufacture of olefins. Acetophenone is used in perfumery as a fragrance ingredient in soaps, detergents, creams, lotions, and perfumes; as a flavouring agent in foods, non-alcoholic beverages, and tobacco; as a specialty solvent for plastics and resins; as a catalyst for the polymerisation of olefins; and as a photosensitiser in organic syntheses. Acetophenone is a raw material for the synthesis of some pharmaceuticals and is also listed as an approved excipient by the U.S. FDA. Acetophenone occurs naturally in many foods such as apple, apricot, banana, and beef. Acetophenone has been detected in ambient air and drinking water; exposure of the general public may occur through the inhalation of contaminated air or the consumption of contaminated water. It is highly flammable and will get easily ignited by heat, sparks, or flames, and the vapours may form explosive mixtures with air.

Chemical properties

Acetophenone is a colorless, oily liquid with a sweet, floral odor.It is a naturally occurring component of a large number of foods and essential oils.
Acetophenone can be hydrogenated catalytically to 1-phenylethanol. It is obtained as a by-product in the Hock phenol synthesis and is purified from the high-boiling residue by distillation. The quantities obtained from this source satisfy the present demand.
Acetophenone is used for perfuming detergents and industrial products and is an intermediate in the synthesis of other fragrance materials.

Chemical properties

Acetophenone has a characteristic sweet, pungent and strong medicinal odor with a bitter, aromatic cherry branch taste. It is useful in flavors of grape, cherry and tobacco

Occurrence

Reported found in cocoa, beef, raspberry, peas, and concord grape

The Uses of Acetophenone

Acetophenone is a reagent used in the production of fragrances and resin polymers. It is used in perfumery, as aphotosensitizer in organic synthesis, and asa catalyst in olefin polymerization.In perfumery to impart an orange-blossom-like odor; in organic syntheses, especially. as photosensitizer.

Definition

ChEBI: Acetophenone is a methyl ketone that is acetone in which one of the methyl groups has been replaced by a phenyl group. It has a role as a photosensitizing agent, an animal metabolite and a xenobiotic.

Preparation

From benzene and acetylchloride in the presence of aluminum chloride or by catalytic oxidation of ethyl benzene; also prepared by fractional distillation and crystallization from the essential oil of Stirlingia latifolia.

Production Methods

Most methyl phenyl ketone originates from the Hock process for the production of phenol from isopropylbenzene (→Phenol); it is isolated from the residue of this process. In addition, acetophenone can be obtained as a main product by selective decomposition of cumene hydroperoxide in the presence of copper catalysts at 100℃:

A second possibility is the oxidation of ethylbenzene with air or oxygen at 130℃ and 0.5 MPa. Catalysts used include cobalt salts or manganese salts of naphthenic or fatty acids. Conversion of ethylbenzene is limited to ca. 25 % to minimize the byproducts 1-phenylethanol and benzoic acid. A third method is the Friedel – Crafts acetylation of benzene with acetic anhydride, but this is not of industrial importance.

Aroma threshold values

Detection: 170 ppb; Recognition: 2.9 ppm

Taste threshold values

Taste characteristics at 10 ppm: sweet, nutty, benzaldehyde with musty, fruity notes

Synthesis Reference(s)

Canadian Journal of Chemistry, 56, p. 2269, 1978 DOI: 10.1139/v78-373
Chemical and Pharmaceutical Bulletin, 31, p. 4209, 1983 DOI: 10.1248/cpb.31.4209

General Description

Acetophenone appears as a colorless liquid with a sweet pungent taste and odor resembling the odor of oranges. Freezes under cool conditions. Slightly soluble in water and denser than water. Hence sinks in water. Vapor heavier than air. A mild irritant to skin and eyes. Vapors can be narcotic in high concentrations. Used as a flavoring, solvent, and polymerization catalyst.

Air & Water Reactions

Slightly soluble in water.

Reactivity Profile

Acetophenone reacts with many acids and bases liberating heat and flammable gases (e.g., H2). Reacts with many oxidizing agents. Reacts with reducing agents such as hydrides, alkali metals, and nitrides to produce flammable gas (H2) and heat. The amount of heat in these reactions may be sufficient to start a fire in the unreacted portion. Incompatible with isocyanates, aldehydes, cyanides, peroxides, and anhydrides.

Health Hazard

Acetophenone is an irritant, mutagen, and amildly toxic compound. In rabbits 0.77 mgproduced severe eye irritation, but the actionon skin was mild. In mice, subcutaneousadministration of this compound producedsleep; a dose of 330 mg/kg was lethal.
LD50 value, intraperitoneal (mice): 200mg/kg
No symptoms of severe toxicity, nor its carcinogenicityin humans, has been reported..

Fire Hazard

Combustible liquid; flash point (closed cup) 82°C (180°F); vapor pressure 1 torr at 37°C (98.6°F); vapor density 4.1 (air = 1); autoignition temperature 570°C (1058°F); fire-extinguishing agent: dry chemical, foam, or CO2; water may cause frothing, but it can be used to flush and dilute the spill. Its reaction with strong oxidizers may be violent.

Flammability and Explosibility

Not classified

Safety Profile

Poison by intraperitoneal and subcutaneous routesModerately toxic by ingestion. A skin and severe eye irritant. Mutation data reported. Narcotic in high concentration. A hypnotic. Flammable liquid. To fight fire, use foam, CO2, dry chemical. When heated to decomposition it emits acrid smoke and fumes. See also IGTONES

Potential Exposure

Acetophenone is used as a solvent and in perfume manufacture to impact a pleasant jasmine or orange-blossom odor. It is used as a catalyst in olefin polymerization and as a flavorant in tobacco. It is also used in the synthesis of pharmaceuticals

Carcinogenicity

No carcinogenicity studies were identified for acetophenone. The U.S. EPA has classified acetophenone as a Category D, not classifiable as to human carcinogenicity.

Environmental Fate

It is unclear what mechanism is responsible for the central nervous system depression observed following high doses of acetophenone. In vitro evaluations have demonstrated that acetophenone suppresses voltage-gated ion channels in olfactory receptor cells and retinal neurons; however, it is unclear if this is related to any of the observed toxicity in animal studies.

Metabolism

At one time, acetophenone was used as a hypnotic. Its conversion to benzoic acid and methylphenylcarbinol in dogs and rabbits was observed by a number of early workers. Small amounts are also excreted as mandelic acid. In the rabbit about half the dose is excreted as methylphenylcarbinyl glucuronide and about 20 % as hippuric acid. It is probable that the ketone is first asymmetrically reduced to the carbinol, which is the precursor of benzoic and mandelic acids.

Solubility in organics

miscible with ethyl alcohol, essential oils and perfume chemicals. Sp.Gr. = 1.033.

Shipping

UN1993 Flammable liquids, n.o.s., Hazard Class: 3; Labels: 3-Flammable liquid, Technical Name Required.

Purification Methods

Dry it by fractional distillation or by standing with anhydrous CaSO4 or CaCl2 for several days, followed by fractional distillation under reduced pressure (from P2O5, optional), and careful, slow and repeated partial crystallisations from the liquid at 0o excluding light and moisture. It can also be crystallised at low temperatures from isopentane. Distillation can be followed by purification using gas-liquid chromatography [Earls & Jones J Chem Soc, Faraday Trans 1 71 2186 1975.] [Beilstein 7 H 271, 7 IV 619.] § A commercial polystyrene supported version is available — scavenger resin (for diol substrates).

Toxicity evaluation

The production and use of acetophenone as a specialty solvent and fragrance and flavor additive may result in environmental releases to the air, water, and soil. Acetophenone is slightly soluble in water and freely soluble in alcohol, chloroform, fatty oils, and glycerol. The vapor pressure at 25 °C is 0.4 mmHg, the Henry’s law constant is estimated to be 1.04×105 atmm3 mol^-1, and the octanol/water partition coefficient (log Kow) is 1.58.
If released to the soil, acetophenone is expected to have high mobility, with volatilization from moist soils. If released to the water, volatilization is anticipated from the surface and acetophenone is not anticipated to adsorb to sediment. The potential for bioconcentration in aquatic organisms is predicted to be low. If released to the atmosphere, the half-life is anticipated to be 6 days, with degradation occurring by reaction with photochemically produced hydroxyl radicals.

Incompatibilities

May form explosive mixture with air. See flash point, above. Reacts violently with strong oxidizers, many acids, bases, amines, amides, and inorganic hydroxides; alkali metals; hydrides, and nitrides. Reacts with reducing agents; alkali metals; hydrides, nitrides. Contact with all preceding materials release heat and flammable gases, including hydrogen; the heat may be sufficient enough to result in fire. Incompatible with aldehydes, aliphatic amines, alkanolamines, cyanides, isocyanates, organic acids, peroxides; perchloric acid. May attack plastics, and some rubbers and coatings

Waste Disposal

Consult with environmental regulatory agencies for guidance on acceptable disposal practices. Generators of waste containing this contaminant (≥100 kg/mo) must conform with EPA regulations governing storage, transportation, treatment, and waste disposal. Incineration, preferably with a flammable solvent

Hazard

Acute (short-term) exposure to acetophenone vapor may produce skin irritation and transient corneal injury in humans. No information is available on the chronic (long-term), reproductive, developmental, or carcinogenic effects of acetophenone in humans. EPA has classified acetophenone as a Group D, not classifiable as to human carcinogenicity.