Title: Acetaldehyde
CAS Registry Number: 75-07-0
Additional Names: Ethanal; "aldehyde"; acetic aldehyde; ethylaldehyde
Molecular Formula: C2H4O
Molecular Weight: 44.05
Percent Composition: C 54.53%, H 9.15%, O 36.32%
Line Formula: CH3CHO
Literature References: Produced by oxidation of alcohol with Na2Cr2O7 and H2SO4; usually from acetylene, dil H2SO4 and mercuric oxide as catalyst; also by passing alcohol vapor over a heated metallic catalyst. Lab procedure from ethanol: Wertheim, J. Am. Chem. Soc. 44, 2658 (1922); Fricke, Havestadt, Angew. Chem. 36, 546 (1923); Gattermann-Wieland, Praxis des Organischen Chemikers (de Gruyter, Berlin, 40th ed., 1961) p 180; from acetylene: Gattermann-Wieland, op. cit. 183; from paraldehyde: A. I. Vogel, Practical Organic Chemistry (Longmans, London, 3rd ed., 1959) p 324; by catalytic oxidation of ethylene in aq soln: J. Smidt et al., Angew. Chem. 71, 176 (1959); by oxidation of ethylene in fuel cells in the gas phase: K. Otsuka et al., Chem. Commun. 1988, 1272. Manuf: Faith, Keyes & Clark's Industrial Chemicals, F. A. Lowenheim, M. K. Moran, Eds. (Wiley-Interscience, New York, 4th ed., 1975) pp 1-7. Toxicity data: Smyth, Arch. Ind. Hyg. Occup. Med. 4, 119 (1951). Review: H. J. Hagemeyer in Kirk-Othmer Encyclopedia of Chemical Technology vol. 1 (John Wiley & Sons, New York, 4th ed., 1991) pp 94-109.
Properties: Flammable liquid; characteristic, pungent odor. d416 0.788. mp -123.5°. bp 21°. nD20 1.3316. Flash pt, closed cup: -36°F (-38°C). Miscible with water, alcohol. Keep cold. Chill thoroughly before opening. LD50 orally in rats: 1930 mg/kg (Smyth).
Melting point: mp -123.5°
Boiling point: bp 21°
Flash point: Flash pt, closed cup: -36°F (-38°C)
Index of refraction: nD20 1.3316
Density: d416 0.788
Toxicity data: LD50 orally in rats: 1930 mg/kg (Smyth)
CAUTION: Potential symptoms of overexposure are eye, nose and throat irritation; conjunctivitis; coughing; CNS depression; eye and skin burns; dermatitis; delayed pulmonary edema. See NIOSH Pocket Guide to Chemical Hazards (DHHS/NIOSH 97-140, 1997) p 2. See also Clinical Toxicology of Commercial Products, R. E. Gosselin et al., Eds. (Williams & Wilkins, Baltimore, 5th ed., 1984) Section II, p 186. This substance is reasonably anticipated to be a human carcinogen: Report on Carcinogens, Eleventh Edition (PB2005-104914, 2004) p III-1.
Use: Manuf 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.
Acetaldehyde Ammonia Acetaldehyde Sodium Bisulfite Acetaldoxime Acetamide Acetamidine Hydrochloride

Lewis structure of acetaldehyde Skeletal structure of acetaldehyde
Ball-and-stick model Space-filling model
CAS number 75-07-0 YesY
PubChem 177
ChemSpider 172 YesY
EC number 200-836-8
KEGG C00084 YesY
ChEBI CHEBI:15343 YesY
RTECS number AB1925000
Jmol-3D images Image 1
Image 2
Molecular formula C2H4O
Molar mass 44.05 g mol−1
Appearance Colourless liquid
Etherial odor
Density 0.784 g·cm−3 (20 °C) [2]

0.7904–0.7928 g·cm−3 (10 °C)[2]

Melting point −123.37 °C; −190.07 °F; 149.78 K
Boiling point 20.2 °C; 68.4 °F; 293.3 K
Solubility in water soluble
Solubility miscible with ethanol, ether, benzene, toluene, xylene, turpentine, acetone
slightly soluble in chloroform
log P -0.34
Acidity (pKa) 13.57
Refractive index (nD) 1.3316
Viscosity ~0.215 at 20 °C
Molecular shape trigonal planar (sp²) at C1
tetrahedral (sp³) at C2
Dipole moment 2.7 D
Std enthalpy of
formation ΔfHo298
−166 kJ·mol−1
Standard molar
entropy So298
250 J·mol−1·K−1
MSDS External MSDS
GHS pictograms GHS-pictogram-flamme.svgGHS-pictogram-exclam.svgGHS-pictogram-silhouete.svg[3]
GHS hazard statements H224, H319, H335, H351[3]
GHS precautionary statements P210, P261, P281, P305+351+338[3]
EU classification Very flammable (F+)
Harmful (Xn)
Carc. Cat. 3
R-phrases R12 R36/37 R40
S-phrases (S2) S16 S33 S36/37
NFPA 704
NFPA 704.svg
Flash point −39.00 °C; −38.20 °F; 234.15 K
Autoignition temperature 185.00 °C; 365.00 °F; 458.15 K
Explosive limits 4.0-60%
LD50 1930 mg/kg (rat, oral)
Related compounds
Related aldehydes Formaldehyde
Related compounds Ethylene oxide
Supplementary data page
Structure and
n, εr, etc.
Phase behaviour
Solid, liquid, gas
Spectral data UV, IR, NMR, MS
 YesY (verify) (what is: YesY/N?)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
Infobox references

Acetaldehyde (systematic name ethanal) is an organic chemical compound with the formula CH3CHO, sometimes abbreviated by chemists as MeCHO (Me = methyl). It is one of the most important aldehydes, occurring widely in nature and being produced on a large scale in industry. Acetaldehyde occurs naturally in coffee, bread, and ripe fruit, and is produced by plants. It is also produced by the partial oxidation of ethanol and may be a contributing factor to hangovers from alcohol consumption, produced in the liver by the enzyme alcohol dehydrogenase. Pathways of exposure include air, water, land, or groundwater, as well as drink and smoke.[4] Consumption of disulfiram inhibits acetaldehyde dehydrogenase, the enzyme responsible for the metabolism of acetaldehyde, thereby causing it to build up in the body.