Chemical Properties
Acetaldehyde is a highly fl
ammable, volatile, colorless liquid. It has a characteristic pun-
gent 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 acetal-
dehyde 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.
Chemical Properties
Colourless clear liquid
Definition
ChEBI: The aldehyde formed from acetic acid by reduction of the carboxy group. It is the most abundant carcinogen in tobacco smoke.
General Description
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.
Reactivity Profile
ACETALDEHYDE(75-07-0) 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(75-07-0) 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].
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.
Health Hazard
Breathing vapors will be irritating and may cause nausea, vomiting, headache, and unconsciousness. Contact with eyes may cause burns and eye damage. Skin contact from clothing wet with the chemical causes burns or severe irritation.
Health Hazard
Exposures to acetaldehyde liquids and vapors for a prolonged period in work areas
cause irritation to the eyes, skin, upper respiratory passages, and bronchi. Continued
exposure is known to damage the corneal epithelium, dermatitis, photophobia, a for-
eign body sensation, and persistent lacrimation or discharge of tears. Acetaldehyde
causes bronchitis and a reduction in the number of pulmonary macrophages. The
severity of lung damage increases with the build up of fl
uid in the lungs (pulmo-
nary edema), and respiratory distress in the worker. Occupational workers exposed
to high concentrations of acetaldehyde suffer coughing, pulmonary edema, necrosis,
photophobia, a foreign body sensation, damage to the nasal mucosa and trachea, and
persistent lacrimation.
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
First aid
If this chemical gets into the eyes remove any contact lenses at once and irrigate immediately for at least 30 minutes, occasionally lifting upper and lower lids. Seek medical attention immediately. If this chemical contacts the skin, quickly remove contaminated clothing. Immediately wash area with large amounts of soap and water. If a person breathes in large amounts of this chemical, move the exposed person to fresh air at once, and perform artificial respiration. Transfer promptly to medical facility. Medical observation is recommended for 24 to 48 hours after breathing overexposure, as pulmonary edema may be delayed. When this chemical has been swallowed, get medical attention. Give large quantities of water and induce vomiting. Do not make an unconscious person vomit.
Shipping
UN1088 Acetaldehyde, Hazard Class: 3; Labels: 3-Flammable liquid.
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.
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 ppbv (Nagata and Takeuchi, 1990) to
0.21 ppmv (Leonardos et al., 1969). Katz and Talbert (1930) reported an experimental detection
odor threshold concentration of 120 μg/m3 (67 ppbv). 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.
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
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.
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.
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.
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.
