Acetaldehyde

Chemical properties

Acetaldehyde is a highly flammable, volatile, colorless liquid. It has a characteristic pungent and suffocating odor, and is miscible in water. Acetaldehyde is ubiquitous in the ambient environment. It is an intermediate product of higher plant respiration and formed as a product of incomplete wood combustion in fi replaces and woodstoves, burning of tobacco, vehicle exhaust fumes, coal refi ning, and waste processing. Exposures to acetaldehyde occur during the production of acetic acid and various other industrial chemical substances. For instance, the manufacture of drugs, dyes, explosives, disinfectants, pheno- lic and urea resins, rubber accelerators, and varnish.

Physical properties

Colorless, mobile, fuming, volatile liquid or gas with a penetrating, pungent odor; fruity odor when diluted. Odor threshold concentrations ranged from 1.5 ppb_v (Nagata and Takeuchi, 1990) to 0.21 ppm_v (Leonardos et al., 1969). Katz and Talbert (1930) reported an experimental detection odor threshold concentration of 120 μg/m³ (67 ppb_v). At low concentrations, acetaldehyde imparts a pleasant, fruity, green apple or leafy green-like flavor (van Aardt et al., 2001). Twenty-five panelists were randomly selected for testing milk products and water for determining flavor thresholds. Flavor threshold concentrations determined by a geometric approach were 3,939 ppb for nonfat milk (0.5% milk fat), 4,020 ppb for low-fat milk (2% milk fat), 4,040 ppb for whole milk, 10,048 ppb for chocolate milk, and 167 ppb for spring water (van Aardt et al., 2001).

Occurrence

Reported.found.in.oak.and.tobacco.leaves;.in.the.fruital.aromas.of.pear,.apple,.raspberry,.strawberry.and.pineapple;.in.the.distillation.waters.of.Monarda punctata, orris,.cumin,.chenopodium;.in.the.essential.oils.of.Litsea cubeba, Magnolia grandiflora, Artemisia brevifolia, rosemary,.balm,.clary.sage,.Mentha arvensis, daffodil,.bitter.orange,.camphor,.angelica,.fennel,. mustard,.Scotch.blended.whiskey,.Japanese.whiskey,.rose.wine,.blackberry.brandy.and.rum.

The Uses of Acetaldehyde

Acetaldehyde is used in producing acetic acid,acetic anhydride, cellulose acetate, syntheticpyridine derivatives, pentaerythritol, terephthalicacid, and many other raw materials.Release of acetaldehyde from poly ethyleneterephthalate (PET) bottles into carbonatedmineral waters has been observed (Lorussoet al. 1985); 180 ppm was detected in sampleskept for 6 months at 40°C (104°F).

The Uses of Acetaldehyde

Acetaldehyde is also known as ethanal, acetaldehyde is miscible with H2O, alcohol, or ether in all proportions. Because of its versatile chemical reactivity, acetaldehyde is widely used as a commencing material in organic syntheses, including the production of resins, dyestuffs, and explosives. The compound also is used as a reducing agent, preservative, and as a medium for silvering mirrors. In resin manufacture, paraldehyde (CH3CHO)3 sometimes is preferred because of its higher boiling and flash points.

The Uses of Acetaldehyde

Acetaldehyde is used as a general solvent in organic and polymer chemical reactions. It also plays a role in fruit and food quality, ripening and deterioration.manufacture of paraldehyde, acetic acid, butanol, perfumes, flavors, aniline dyes, plastics, synthetic rubber; silvering mirrors, hardening gelatin fibers. Flavoring agent in foods and beverages. Fumigant for storage of apples and strawberries.

Definition

ChEBI: Acetaldehyde is the aldehyde formed from acetic acid by reduction of the carboxy group. It is the most abundant carcinogen in tobacco smoke. It has a role as a human metabolite, an EC 3.5.1.4 (amidase) inhibitor, a carcinogenic agent, a mutagen, a teratogenic agent, an oxidising agent, an electron acceptor, a Saccharomyces cerevisiae metabolite, an Escherichia coli metabolite and a mouse metabolite.

Production Methods

The main production method is the Hoeschst–Wacker twostage process, in which acetaldehyde is generated by oxidizing ethylene with aqueous palladium chloride over a copper catalyst. Some acetaldehyde is also produced by oxidation of ethanol.

Aroma threshold values

Detection:.0.7.to.200.ppb;.Recognition:.27.to.380.ppb

General Description

Acetaldehyde appears as a clear colorless liquid with a pungent choking odor. Flash point -36 °F. Boiling point 69 °F. Density 6.5 lb / gal. Vapors are heaver than air and irritate the mucous membranes and especially the eyes. Used to make other chemicals.

Air & Water Reactions

Highly flammable. Easily oxidized by air to form unstable peroxides which may explode. Forms explosive mixture with air above 100°C (30-60% of the vapor in air) owing to formation of peroxyacetic acid [White, A. G. et al., J. Soc. Chem. Ind., 1950, 69, p. 206]. Soluble in water.

Reactivity Profile

Acetaldehyde undergoes a vigorously exothermic condensation reaction in contact with strong acids, bases or traces of metals. Can react vigorously with oxidizing reagents such as dinitrogen pentaoxide, hydrogen peroxide, oxygen, silver nitrate, etc. Contamination often leads either to reaction with the contaminant or polymerization, both with the evolution of heat. Can react violently with acid anhydrides, alcohols, ketones, phenols, ammonia, hydrogen cyanide, hydrogen sulfide, halogens, phosphorus, isocyanates, concentrated sulfuric acid, and aliphatic amines. Reactions with cobalt chloride, mercury(II) chlorate or perchlorate form sensitive, explosive products [Sax, 9th ed., 1996, p. 5]. An oxygenation reaction of Acetaldehyde in the presence of cobalt acetate at -20°C exploded violently when stirred. The event was ascribed to peroxyacetate formation [Phillips B. et al., J. Am. Chem. Soc., 1957, 79, p. 5982].

Health Hazard

The acute toxicity of acetaldehyde is low by inhalation and moderate by ingestion. Exposure to acetaldehyde by inhalation is irritating to the respiratory tract and mucous membranes; this substance is a narcotic and can cause central nervous system depression. Ingestion of acetaldehyde may cause severe irritation of the digestive tract leading to nausea, vomiting, headache, and liver damage. Acetaldehyde causes irritation and burning upon skin contact and is a severe eye irritant.br Acetaldehyde has caused nasal tumors in rats exposed by inhalation and is listed by IARC in Group 2B ("possible human carcinogen"). It is not classified as a "select carcinogen" according to the criteria of the OSHA Laboratory Standard. Acetaldehyde is mutagenic and has been shown to be a reproductive toxin in animals. Acetaldehyde is formed by metabolism of ethanol, and chronic exposure can produce symptoms similar to alcoholism.

Health Hazard

Acetaldehyde is moderately toxic throughinhalation and ingestion routes. Ingestion canresult in conjunctivitis, central nervous system(CNS) depression, eye and skin burns,and dermatitis. Large doses can be fatal.Because of its metabolic link to ethanol,its intoxication consequences are similar tothose of chronic ethanol intoxication.
Inhalation can produce irritation of theeyes, nose, and throat, and narcotic effects.High concentrations can cause headache,sore throat, and paralysis of respiratory muscles.Prolonged exposure can raise bloodpressure and cause a decrease in red andwhite blood cells. A 4-hour exposure to 1.6%acetaldehyde in air was lethal to rats (ACGIH1986).
The functional groups- NH2,-OH, and-SH in the three-dimensional protein moleculesare susceptible to CHO attack. Acetaldehydecan therefore bind to liver proteinand hemoglobin to form stable adducts.Such covalent binding probably alters thebiological functions of protein and hemoglobinand thus contributes to its toxicity.Rats subjected to inhalation of acetaldehydefor 21 days showed the presence of such“bound” aldehyde adducts in their intracellularmedium. A control experiment on unexposedrats, however, showed similar adducts,but at a low concentration. This could probablyhave formed from trace aldehyde generatedfrom intestinal microbial fermentationof alcohols.
In a study on chronic inhalation toxicityof acetaldehyde on rats, the compound wasfound to effect increased mortality, growthretardation, and nasal tumors (Woutersenet al. 1986). The study indicates that acetaldehydeis both cytotoxic and carcinogenic tothe nasal mucosa of rats. Investigating thetoxicity of tobacco-related aldehydes in culturedhuman bronchial epithelial cells, Graftstromet al. (1985) reported that acetaldehydewas weakly cytotoxic, less so than acroleinand formaldehyde.

Fire Hazard

Acetaldehyde is a dangerous fire hazard (NFPA rating = 4) owing to its volatility and low autoignition temperature. Its vapor is explosive in the concentration range 4 to 66% in air and may be ignited by hot surfaces such as hot plates or light bulbs, or by static electricity discharges. The vapor is heavier than air and may travel a considerable distance to an ignition source and "flash back." Carbon dioxide or dry chemical extinguishers should be used to fight acetaldehyde fires.

Flammability and Explosibility

Acetaldehyde is a dangerous fire hazard (NFPA rating = 4) owing to its volatility and low autoignition temperature. Its vapor is explosive in the concentration range 4 to 66% in air and may be ignited by hot surfaces such as hot plates or light bulbs, or by static electricity discharges. The vapor is heavier than air and may travel a considerable distance to an ignition source and "flash back." Carbon dioxide or dry chemical extinguishers should be used to fight acetaldehyde fires.

Contact allergens

Acetaldehyde, as its metabolite, is responsible for many of the effects of ethanol, such as hepatic or neurological toxicity. A case of contact allergy was reported in the textile industry, where dimethoxane was used as a biocide agent in textiles, and its degradation led to acetaldehyde

Safety Profile

Confirmed carcinogen with experimental carcinogenic and tumorigenic data. Poison by intratracheal and intravenous routes. A human systemic irritant by inhalation. An experimental routes. A human systemic irritant by inhalation. An experimental teratogen. Other experimental reproductive effects. A skin and severe eye irritant. A narcotic. Human mutation data reported. A common air contaminant. Highly flammable liquid. Mixtures of 30-60% of the vapor in air ignite above 100℃. It can react violently with acid anhydrides, alcohols, ketones, phenols, NH3, HCN, H2S, halogens, P, isocyanates, strong alkalies, and amines. Reactions with cobalt chloride, mercury(Ⅱ) chlorate, or mercury(Ⅱ) perchlorate form violently in the presence of traces of metals or acids. Reaction with oxygen may lead to detonation. When heated to decomposition it emits acrid smoke and fumes.

Synthesis

The.method.of.synthesis.is.dependent.on.the.price.of.feedstock.and.may.be.produced.by.a.number.of.methods:.(1).by. oxidation.of.ethyl.alcohol.with.potassium.dichromate.or.manganese.dioxide.in.the.presence.of.sulfuric.acid;.(2).by.addition.of.water. to.acetylene;.(3).by.formation.during.the.natural.alcoholic.fermentation.process..Recovery.is.effected.by.suitable.fractionation,.subsequent.preparation.of.the.acetaldehyde.ammonia.and.final.treatment.of.the.addition.compound.with.diluted.sulfuric.acid.

Potential Exposure

Acetaldehyde is used as a chemical intermediate and can be found in many processed foods; in crafts, arts, automotive, and home improvement products

Carcinogenicity

Acetaldehyde is reasonably anticipated to be a human carcinogenbased on sufficient evidence of carcinogenicity from studies in experimental animals.

Source

Manufactured by oxidizing ethanol with sodium dichromate and sulfuric acid or from acetylene, dilute sulfuric acid, and mercuric oxide catalyst.
Acetaldehyde was detected in diesel fuel at a concentration of 41,800 μg/g (Schauer et al., 1999). Identified as an oxidative degradation product in the headspace of a used engine oil (10 to 30W) after 4,080 miles (Levermore et al., 2001).
Acetaldehyde occurs naturally in many plant species including Merrill flowers (Telosma cordata), in which it was detected at a concentration of 1,026 ppm (Furukawa et al., 1993). In addition, acetaldehyde was detected in witch hazel leaves (160 ppm), orange juice (3 to 15 ppm), tangerines (0 to 2 ppm), pineapples (0.61–1.4 ppm), celery leaves, coffee seeds, cantaloupes, soybeans, carrot roots, tomatoes, tobacco leaves, apples, peaches, black currant, fishwort, peppermint, rice plants, and caraway (Duke, 1992). Acetaldehyde was detected in tobacco smoke and marijuana at concentrations of 980 and 1,200 μg/cigarette, respectively (Hoffman et al., 1975). The oil of alfalfa contained acetaldehyde at an approximate concentration of 0.2% (Kami, 1983). Also detected among 139 volatile compounds identified in cantaloupe (Cucumis melo var. reticulates cv. Sol Real) using an automated rapid headspace solid phase microextraction method (Beaulieu and Grimm, 2001). In hand-squeezed grapefruit, acetaldehyde was detected at a concentration of 6,150 μg/kg (Buettner and Schieberle, 2001).
Schauer et al. (2001) measured organic compound emission rates for volatile organic compounds, gas-phase semi-volatile organic compounds, and particle phase organic compounds from the residential (fireplace) combustion of pine, oak, and eucalyptus. The gas-phase emission rates of acetaldehyde were 1,704 mg/kg of pine burned, 823 mg/kg of oak burned, and 1,021 mg/kg of eucalyptus burned.
Gas-phase tailpipe emission rates from California Phase II reformulated gasoline-powered automobiles with and without catalytic converters were 3.94 and 301 mg/km, respectively (Schauer et al., 2002).
Acetaldehyde is a degradation product of poly(ethylene terephthalate) during the melt processing packaging for milk, water, and other beverage products. Occurs in many food products such as yogurt and vinegar at concentrations up to 1,000 mg/L (van Aardt et al., 2001).
Acetaldehyde is a key ingredient in yogurt and is formed during milk fermentation by microorganisms. Acetaldehyde is present in other fermented products such as cheese, butter, and buttermilk (Ott et al., 2000).

Environmental Fate

Biological. Heukelekian and Rand (1955) reported a 5-d BOD value of 1.27 g/g that is 69.8% of the ThOD value of 1.82 g/g.
Photolytic. Photooxidation of acetaldehyde in nitrogen oxide-free air using radiation between 2900 to 3500 ? yielded hydrogen peroxide, alkyl hydroperoxides, carbon monoxide, and lower molecular weight aldehydes. In the presence of nitrogen oxides, photooxidation products include ozone, hydrogen peroxide, and peroxyacyl nitrates (Kopczynski et al., 1974). Anticipated products from the reaction of acetaldehyde with ozone or OH radicals in the atmosphere are formaldehyde and carbon dioxide (Cupitt, 1980). Reacts with nitrogen dioxide forming peroxyacyl nitrates, formaldehyde, and methyl nitrate (Altshuller, 1983). Irradiation in the presence of chlorine yielded peroxyacetic acid, carbon monoxide, and carbon dioxide (acetaldehyde into formic acid, methyl nitrate, and peroxyacetal nitrate (Cox et al., 1980).
Chemical/Physical. Oxidation in air yields acetic acid (Windholz et al., 1983). In the presence of sulfuric, hydrochloric, or phosphoric acids, polymerizes explosively forming trimeric paraldehyde (Huntress and Mulliken, 1941; Patnaik, 1992). In an aqueous solution at 25 °C, acetaldehyde is partially hydrated, i.e., 0.60 expressed as a mole fraction, forming a gem-diol (Bell and McDougall, 1960). Acetaldehyde decomposes at temperatures greater than 400 °C, forming carbon monoxide and methane (Patnaik, 1992).

storage

Acetaldehyde should be used only in areas free of ignition sources, and quantities greater than 1 liter should be stored in tightly sealed metal containers in areas separate from oxidizers. Acetaldehyde should always be stored under an inert atmosphere of nitrogen or argon to prevent autoxidation.

Shipping

UN1088 Acetaldehyde, Hazard Class: 3; Labels: 3-Flammable liquid.

Purification Methods

Acetaldehyde is usually purified by fractional distillation in a glass helices-packed column under dry N2, discarding the first portion of distillate. Or, it is shaken for 30minutes with NaHCO3, dried with CaSO4 and fractionally distilled at 760mm through a 70cm Vigreux column (p 11). The middle fraction is collected and further purified by standing for 2hours at 0o with a small amount of hydroquinone (free radical inhibitor), followed by distillation [Longfield & Walters J Am Chem Soc 77 810 1955]. [Beilstein 1 IV 3094.]

Toxicity evaluation

Industrial exposures to acetaldehyde are most likely to occur by inhalation with potential for skin and eye contact. Accidental ingestion is also possible. The main source of exposure to acetaldehyde in humans is alcohol consumption and to a lesser extent from air, vehicle exhaust, and from various industrial wastes. Degradation of hydrocarbons, sewage, and solid biological wastes produces acetaldehyde, as well as the open burning and incineration of gas, fuel oil, and coal.

Incompatibilities

Reacts with air to form unstable peroxides which can explode. Contact with air causes acetaldehyde to chemically degrade to acetic acid. Strong oxidizers, acids, bases, alcohols, ammonia, amines, halogens, phenols, acid anhydrides, ketones, hydrogen cyanide, hydrogen sulfide. May dissolve rubber. Slightly corrosive to mild steel. May explode without warning when exposed to heat, dust, corrosives, or oxidizers.

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.