Acetaldehyde
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2008-07-03T04:30:47Z
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{{Chembox new
| Name = '''Acetaldehyde'''
| ImageFileL1 = Acetaldehyde-tall-2D-skeletal.png
| ImageSizeL1 = 75px
| ImageNameL1 = Chemical structure of acetaldehyde
| ImageFileR1 = Acetaldehyde-3D-balls.png
| ImageSizeR1 = 120px
| ImageNameR1 = Chemical structure of acetaldehyde
| ImageFile2 = Acetaldehyde-3D-vdW.png
| ImageSize2 = 150px
| ImageName2 = Three-dimensional structure of acetaldehyde
| IUPACName = acetaldehyde
| SystematicName = ethanal
| Section1 = {{Chembox Identifiers
| SMILES = CC=O
| CASNo = 75-07-0
| EINECS = 200-836-8
| RTECS = AB1925000
}}
| Section2 = {{Chembox Properties
| Formula = C<sub>2</sub>H<sub>4</sub>O
| MolarMass = 44.05 g mol<sup>−1</sup>
| Appearance = Colorless liquid<br />Pungent, fruity odor
| Density = 0.788 g cm<sup>−3</sup>
| Solubility = soluble in all proportions
| MeltingPt = −123.5 °C
| BoilingPt = 20.2 °C
| Viscosity = ~0.215 at 20 °C
}}
| Section3 = {{Chembox Structure
| MolShape = trigonal planar (sp²) at C<sub>1</sub><br />tetrahedral (sp³) at C<sub>2</sub>
| Dipole = 2.7 [[Debye|D]]
}}
| Section7 = {{Chembox Hazards
| EUClass = Very flammable ('''F+''')<br />Harmful ('''Xn''')<br />[[Carcinogen|Carc. Cat. 3]]
| NFPA-H = 2
| NFPA-F = 4 | Reactivity=2
| NFPA-R =
| RPhrases = {{R12}}, {{R36/37}}, {{R40}}
| SPhrases = {{S2}}, {{S16}}, {{S33}}, {{S36/37}}
| FlashPt = −39 °C
| Autoignition = 185 °C
}}
| Section8 = {{Chembox Related
| Function = [[aldehyde]]s
| OtherFunctn = [[Formaldehyde]]<br /> [[Propionaldehyde]]<br /> [[Ethylene oxide]]
}}
}}
'''Acetaldehyde''', sometimes known as '''ethanal''', is an [[organic compound|organic chemical compound]] with the [[chemical formula|formula]] [[Carbon|C]][[Hydrogen|H]]<sub>3</sub>CH[[Oxygen|O]] or MeCHO. It is a flammable liquid with a fruity smell. Acetaldehyde occurs naturally in ripe [[fruit]], [[coffee]], and fresh [[bread]], and is produced by [[plant]]s as part of their normal [[metabolism]]. It is popularly known as the chemical that causes [[hangover]]s.<ref>[http://health.howstuffworks.com/hangover4.htm How Hangovers Work], [[HowStuffWorks]]</ref>
In the chemical industry, acetaldehyde is used as an intermediate in the production of [[acetic acid]], certain [[ester]]s, and a number of other chemicals. In 1989, US production stood at 740 million pounds (336,000 Mg).{{Fact|date=February 2007}} An important production method for acetaldehyde is the [[Wacker process]].
== Biological aspects ==
In the [[liver]], the [[enzyme]] [[alcohol dehydrogenase]] converts ethanol into acetaldehyde, which is then further converted into harmless [[acetic acid]] by [[acetaldehyde dehydrogenase]]. The last steps of alcoholic [[fermentation (food)|fermentation]] in [[bacterium|bacteria]], [[plant]]s and [[yeast]] involve the conversion of [[pyruvate]] into acetaldehyde by the enzyme [[pyruvate decarboxylase]], followed by the conversion of acetaldehyde into ethanol. The latter reaction is again catalyzed by an alcohol dehydrogenase, now operating in the opposite direction.
=== Acetaldehyde and hangovers ===
Most people of [[East Asia]]n descent have a [[mutation]] in their [[alcohol dehydrogenase]] [[gene]] that makes this enzyme unusually effective at converting ethanol to acetaldehyde, and about half of such people also have a form of [[acetaldehyde dehydrogenase]] that is less effective at converting acetaldehyde to acetic acid.<ref>{{cite journal |author=Xiao Q, Weiner H, Crabb DW |title=The mutation in the mitochondrial aldehyde dehydrogenase (ALDH2) gene responsible for alcohol-induced flushing increases turnover of the enzyme tetramers in a dominant fashion |journal=J. Clin. Invest. |volume=98 |issue=9 |pages=2027–32 |year=1996 |pmid=8903321 |url=http://www.jci.org/cgi/content/abstract/98/9/2027 |doi=10.1172/JCI119007}}</ref> This combination causes them to suffer from the [[alcohol flush reaction]], in which acetaldehyde accumulates after drinking, leading to severe and immediate hangover symptoms. These people are therefore less likely to become [[alcoholic]]s. The drug [[disulfiram]] (Antabuse) also prevents the oxidation of acetaldehyde to acetic acid, with the same unpleasant effects for drinkers. It is used in the treatment of alcoholism.
== Applications in organic synthesis ==
Acetaldehyde is a common 2-carbon building block in [[organic synthesis]].<ref>Sowin, T. J.; Melcher, L. M. ”Acetaldehyde” in Encyclopedia of Reagents for Organic Synthesis (Ed: L. Paquette) 2004, J. Wiley & Sons, New York. {{DOI|10.1002/047084289}}</ref> Because of its small size and its availability as the anhydrous monomer (unlike formaldehyde), it is a common electrophile. With respect to its condensation reactions, acetaldehyde is [[prochiral]]. It is mainly used as a source of the CH<sub>3</sub>C<sup>+</sup>H(OH) [[synthon]] in [[aldol condensation|aldol]] and related condensation reactions.<ref>{{OrgSynth | author = Behrens, C.; Paquette, L. A. | title = N-Benzyl-2,3-Azetidinedione | collvol = 10 | collvolpages = 41 | year = 2004 | prep = V75P0106}}</ref> Grignard reagents and organolithium compounds react with MeCHO to give hydroxyethyl derivatives.<ref>{{OrgSynth | author = Walter, L. A. | title = 1-(α-Pyridyl)-2-Propanol | collvol = 3 | collvolpages = 757 | year = 1955 | prep = cv3p0757}}</ref> In one of the more spectacular condensation reactions, three equivalents of [[formaldehyde]] add to MeCHO to give [[pentaerythritol]], C(CH<sub>2</sub>OH)<sub>4</sub>.<ref>{{OrgSynth | author = Schurink, H. B. J. | title = Pentaerythritol | collvol = 1 | collvolpages = 425 | year = 1941 | prep = CV1P0425}}</ref>
In a [[Strecker amino acid synthesis|Strecker reaction]], acetaldehyde condenses with [[cyanide]] and [[ammonia]] to give, after [[hydrolysis]], the [[amino acid]] alanine.<ref>{{OrgSynth | author = Kendall, E. C. McKenzie, B. F. | title = ''dl''-Alanine | collvol = 1 | collvolpages = 21 | year = 1941 | prep = CV1P0021}}</ref> Acetaldehyde can condense with amines to yield imines, such as the condensation with cyclohexylamine to give N-ethylidenecyclohexylamine. These imines can be used to direct subsequent reactions like an aldol condensation.<ref>{{OrgSynth | author = [[Georg Wittig|Wittig, G.]]; Hesse, A. | title = Directed Aldol Condensations: β-Phenylcinnamaldehyde | collvol = 6 | collvolpages = 901 | year = 1988 | prep = cv6p0901}}</ref>
It is also an important building block for the synthesis of [[heterocyclic compounds]]. A remarkable example is its conversion upon treatment with [[ammonia]] to 5-ethyl-2-methylpyridine ("aldehyde-collidine”).<ref>{{OrgSynth | author = Frank, R. L.; Pilgrim, F. J.; Riener, E. F. | title = 5-Ethyl-2-Methylpyridine | collvol = 4 | collvolpages = 451 | year = 1963 | prep = CV4P0451}}</ref>
=== Acetal derivatives ===
Three molecules of acetaldehyde condense to form “[[paraldehyde]],” a cyclic trimer containing C-O single bonds; four condense to form the cyclic molecule called [[metaldehyde]].
Acetaldehyde forms a stable [[acetal]] upon reaction with [[ethanol]] under conditions that favor dehydration. The product, CH<sub>3</sub>CH(OCH<sub>2</sub>CH<sub>3</sub>)<sub>2</sub>, is in fact called "acetal,"<ref>{{OrgSynth | author = Adkins, H.; Nissen, B. H. | title = Acetal | collvol = 1 | collvolpages = 1 | year = 1941 | prep = CV1P0001}}</ref> although [[acetal]] is used more widely to describe other compounds with the formula RCH(OR')<sub>2</sub>.
== Ethenol ==
Only a trace of acetaldehyde exists as the [[enol]] form, [[ethenol]], with K<sub>eq</sub> = 6 x 10<sup>-5</sup>.<ref>March, J. “Organic Chemistry: Reactions, Mechanisms, and Structures” J. Wiley, New York: 1992. ISBN 0-471-58148-8.</ref>
== Environmental occurrence ==
Acetaldehyde is an [[air pollution|air pollutant]] resulting from combustion, such as automotive exhaust and [[tobacco smoking|tobacco smoke]]. It is also created by [[thermal degradation]] of polymers in the [[plastics]] processing industry. <ref>''[http://www.britannica.com/eb/article-242792 Smoking]''. (2006). [[Encyclopædia Britannica]]. Accessed 27 Oct 2006.</ref>
== Safety ==
Acetaldehyde is toxic when applied externally for prolonged periods, an irritant, and a probable [[carcinogen]].<ref>[http://www.epa.gov/chemfact/s_acetal.txt Chemical Summary For Acetaldehyde], US Environmental Protection Agency</ref>
== References ==
<references/>
== See also ==
* [[Wine fault]]
== External links ==
* [http://www.ilo.org/public/english/protection/safework/cis/products/icsc/dtasht/_icsc00/icsc0009.htm International Chemical Safety Card 0009]
* [http://www.npi.gov.au/database/substance-info/profiles/1.html National Pollutant Inventory - Acetaldehde]
* [http://www.cdc.gov/niosh/npg/npgd0001.html NIOSH Pocket Guide to Chemical Hazards]
* [http://www-cie.iarc.fr/htdocs/monographs/vol71/005-acetaldehyde.html IARC Monograph: "Acetaldehyde"]
* Hal Kibbey, [http://www.indiana.edu/~rcapub/v17n3/p18.html Genetic Influences on Alcohol Drinking and Alcoholism], Indiana University Research and Creative Activity, Vol. 17 no. 3.
* [http://www.grokfood.com/additives/2.htm United States Food and Drug Administration (FDA) information for acetaldehyde]
[[Category:flavors]]
[[Category:Aldehydes]]
[[Category:Hazardous air pollutants]]
[[Category:IARC Group 2B carcinogens]]
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