Acetaldehyde: Wikis

  

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Acetaldehyde
Skeletal structure of acetaldehyde
Skeletal structure of acetaldehyde
Lewis structure of acetaldehyde
Three-dimensional structure of acetaldehyde
IUPAC name
Systematic name Ethanal
Other names Acetic Aldehyde
Ethyl Aldehyde[1]
Identifiers
CAS number 75-07-0 Yes check.svgY
PubChem 177
EC number 200-836-8
RTECS number AB1925000
SMILES
InChI
InChI key IKHGUXGNUITLKF-UHFFFAOYAB
ChemSpider ID 172
Properties
Molecular formula C2H4O
Molar mass 44.05 g mol−1
Appearance Colorless liquid
Pungent, fruity odor
Density 0.788 g cm−3
Melting point

−123.5 °C, 150 K, -190 °F

Boiling point

20.2 °C, 293 K, 68 °F

Solubility in water soluble in all proportions
Viscosity ~0.215 at 20 °C
Structure
Molecular shape trigonal planar (sp²) at C1
tetrahedral (sp³) at C2
Dipole moment 2.7 D
Hazards
MSDS External MSDS
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
4
3
2
 
Flash point 234,15 K (-39 °C)
Autoignition
temperature
458,15 K (185 °C)
Related compounds
Related aldehydes Formaldehyde
Propionaldehyde
Related compounds Ethylene oxide
Supplementary data page
Structure and
properties
n, εr, etc.
Thermodynamic
data
Phase behaviour
Solid, liquid, gas
Spectral data UV, IR, NMR, MS
 Yes check.svgY (what is this?)  (verify)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Acetaldehyde (systematically: ethanal) is an organic chemical compound with the formula CH3CHO or MeCHO. It is a flammable liquid. Acetaldehyde occurs naturally in coffee, bread, and ripe fruit, and is produced by plants as part of their normal metabolism. It is also produced by oxidation of ethanol, and is popularly believed to be a chemical that causes hangovers.[2]

Contents

Structure

Like other carbonyl compounds, acetaldehyde tautomerizes to give the enol, ethenol, with Keq = 6 x 10−5.[3]

Production

In the chemical industry, acetaldehyde is used as an intermediate in the production of acetic acid, certain esters, and a number of other chemicals. In 1989, US production stood at 740 million pounds (336,000 tonnes).[4] An important production method for acetaldehyde is the Wacker process. The hydration of acetylene, catalyzed by mercury salts gives ethenol, which tautomerizes to acetaldehyde. This process was conducted on an industrial scale prior to the Wacker process.[5]

Reactions

Acetaldehyde is a common 2-carbon building block in organic synthesis.[6] 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 CH3C+H(OH) synthon in aldol and related condensation reactions.[7] Grignard reagents and organolithium compounds react with MeCHO to give hydroxyethyl derivatives.[8] In one of the more spectacular condensation reactions, three equivalents of formaldehyde add to MeCHO to give pentaerythritol, C(CH2OH)4.[9]

In a Strecker reaction, acetaldehyde condenses with cyanide and ammonia to give, after hydrolysis, the amino acid alanine.[10] 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.[11]

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”).[12]

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, CH3CH(OCH2CH3)2, is in fact called "acetal,"[13] although acetal is used more widely to describe other compounds with the formula RCH(OR')2.

Biochemistry and health effects

In the liver, the enzyme alcohol dehydrogenase oxidizes ethanol into acetaldehyde, which is then further oxidized into harmless acetic acid by acetaldehyde dehydrogenase. These two oxidation reactions are coupled with the reduction of NAD+ to NADH[14]. In the brain, alcohol dehydrogenase has a minor role in the oxidation of ethanol to acetaldehyde. Instead, the enzyme catalase primarily oxidizes ethanol to acetaldehyde[15]. The last steps of alcoholic fermentation in bacteria, plants 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.

Hangover

Most people of East Asian 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.[16] This combination causes them to suffer from alcohol flush reaction, in which acetaldehyde accumulates after drinking, leading to immediate and severe hangover symptoms. These people are therefore less likely to become alcoholics.[17][18]

The drug disulfiram (Antabuse) prevents the oxidation of acetaldehyde to acetic acid, and it has the same unpleasant effect on drinkers. Antabuse is used as a deterrent for alcoholics who wish to stay sober.

Tobacco addiction

Acetaldehyde is a significant constituent of tobacco smoke. It has been demonstrated to have a synergistic effect with nicotine, increasing the onset and tenacity of addiction to cigarette smoking, particularly in adolescents.[19][20]

Alzheimer's disease

People who have a genetic deficiency for the conversion of acetaldehyde into acetic acid may have a greater risk of Alzheimer's disease. "These results indicate that the ALDH2 deficiency is a risk factor for LOAD [late-onset Alzheimer's disease] …"[21]

Organ Disease

Acetaldehyde has the capability to bind to certain proteins. After ethanol is consumed, acetaldehyde binds to proteins to form adducts. These adducts are linked to organ disease[22].

Neuronal Damage

When acetaldehyde is present in the brain, it binds to proteins in the brain to form adducts. Acetaldehyde adducts are found in the frontal cortex and midbrain of alcoholics. These adducts cause neuronal damage. They can cause neurons and their related synaptic receptors to disappear[23].

Carcinogen

Acetaldehyde is a probable carcinogen in humans.[24] The International Agency for Research on Cancer states, "There is sufficient evidence for the carcinogenicity of acetaldehyde (the major metabolite of ethanol) in experimental animals."[25] In addition, acetaldehyde is damaging to DNA[26] and causes abnormal muscle development as it binds to proteins.[27]

A study of 818 heavy drinkers found that those who are exposed to more acetaldehyde than normal through a defect in the gene for alcohol dehydrogenase are at greater risk of developing cancers of the upper gastrointestinal tract and liver.[28]

Safety

Acetaldehyde is toxic when applied externally for prolonged periods, an irritant, and a probable carcinogen.[29]

Acetaldehyde is an air pollutant resulting from combustion, such as automotive exhaust and tobacco smoke. It is also created by thermal degradation of polymers in the plastics processing industry. [30]

See also

References

  1. ^ SciFinderScholar (accessed Nov 4, 2009). Acetaldehyde (75-07-0) Substance Detail.
  2. ^ How Hangovers Work, HowStuffWorks
  3. ^ March, J. “Organic Chemistry: Reactions, Mechanisms, and Structures” J. Wiley, New York: 1992. ISBN 0-471-58148-8.
  4. ^ "CHEMICAL SUMMARY FOR ACETALDEHYDE". OFFICE OF POLLUTION PREVENTION AND TOXICS. August 1994. http://www.epa.gov/chemfact/s_acetal.txt.  
  5. ^ Dmitry A. Ponomarev and Sergey M. Shevchenko (2007). "Hydration of Acetylene: A 125th Anniversary". J. Chem. Ed. 84 (10): 1725. doi:10.1021/ed084p1725. http://jchemed.chem.wisc.edu/HS/Journal/Issues/2007/OctACS/ACSSub/p1725.pdf.  
  6. ^ 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
  7. ^ Behrens, C.; Paquette, L. A. (2004), "N-Benzyl-2,3-Azetidinedione", Org. Synth., http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=V75P0106  ; Coll. Vol. 10: 41  
  8. ^ Walter, L. A. (1955), "1-(α-Pyridyl)-2-Propanol", Org. Synth., http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=cv3p0757  ; Coll. Vol. 3: 757  
  9. ^ Schurink, H. B. J. (1941), "Pentaerythritol", Org. Synth., http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=CV1P0425  ; Coll. Vol. 1: 425  
  10. ^ Kendall, E. C. McKenzie, B. F. (1941), "dl-Alanine", Org. Synth., http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=CV1P0021  ; Coll. Vol. 1: 21  
  11. ^ Wittig, G.; Hesse, A. (1988), "Directed Aldol Condensations: β-Phenylcinnamaldehyde", Org. Synth., http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=cv6p0901  ; Coll. Vol. 6: 901  
  12. ^ Frank, R. L.; Pilgrim, F. J.; Riener, E. F. (1963), "5-Ethyl-2-Methylpyridine", Org. Synth., http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=CV4P0451  ; Coll. Vol. 4: 451  
  13. ^ Adkins, H.; Nissen, B. H. (1941), "Acetal", Org. Synth., http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=CV1P0001  ; Coll. Vol. 1: 1  
  14. ^ Hipolito, L.; Sanchez, M. J.; Polache, A.; Granero, L. Brain metabolism of ethanol and alcoholism: An update. Curr. Drug Metab. 2007, 8, 716-727.
  15. ^ Hipolito, L.; Sanchez, M. J.; Polache, A.; Granero, L. Brain metabolism of ethanol and alcoholism: An update. Curr. Drug Metab. 2007, 8, 716-727.
  16. ^ Xiao Q, Weiner H, Crabb DW (1996). "The mutation in the mitochondrial aldehyde dehydrogenase (ALDH2) gene responsible for alcohol-induced flushing increases turnover of the enzyme tetramers in a dominant fashion". J. Clin. Invest. 98 (9): 2027–32. doi:10.1172/JCI119007. PMID 8903321. PMC 507646. http://www.jci.org/cgi/content/abstract/98/9/2027.  
  17. ^ Earleywine, Mitchell (1999). Mind-Altering Drugs: The Science of Subjective Experience. OUP USA. p. 163. ISBN 978-0195165319.  
  18. ^ http://www.annals.org/cgi/content/full/127/5/376
  19. ^ [http://drugabuse.gov/NIDA_notes/NNvol20N3/Study.html Study Points to Acetaldehyde-Nicotine Combination In Adolescent Addiction]
  20. ^ Nicotine's addictive hold increases when combined with other tobacco smoke chemicals, UCI study finds
  21. ^ "Mitochondrial ALDH2 Deficiency as an Oxidative Stress". Annals of the New York Academy of Sciences 1011: 36–44. April 2004. doi:10.1196/annals.1293.004. PMID 15126281. http://www3.interscience.wiley.com/journal/118765604/abstract?CRETRY=1&SRETRY=0. Retrieved 2009-08-13.  
  22. ^ Nakamura, K.; Iwahashi, K.; Furukawa, A.; Ameno, K.; Kinoshita, H.; Ijiri, I.; Sekine, Y.; Suzuki, K.; Iwata, Y.; Minabe, Y.; Mori, N. Acetaldehyde adducts in the brain of alcoholics. Arch. Toxicol. 2003, 77, 591.
  23. ^ Nakamura, K.; Iwahashi, K.; Furukawa, A.; Ameno, K.; Kinoshita, H.; Ijiri, I.; Sekine, Y.; Suzuki, K.; Iwata, Y.; Minabe, Y.; Mori, N. Acetaldehyde adducts in the brain of alcoholics. Arch. Toxicol. 2003, 77, 591.
  24. ^ Chemical Summary For Acetaldehyde, US Environmental Protection Agency
  25. ^ International Agency for Rescarch on Cancer, World Health Organization. (1988). Alcohol drinking. Lyon: World Health Organization, International Agency for Research on Cancer. ISBN 92-832-1244-4. http://monographs.iarc.fr/ENG/Monographs/vol44/volume44.pdf.   p3
  26. ^ http://www.ist-world.org/ResultPublicationDetails.aspx?ResultPublicationId=2c488c559db74d8cae0c14ae5b65e14e
  27. ^ Nicholas S. Aberle, II, Larry Burd, Bonnie H. Zhao and Jun Ren (2004). "Acetaldehyde-induced cardiac contractile dysfunction may be alleviated by vitamin b1 but not by vitamins B6 or B12". Alcohol & Alcoholism 39 (5): 450–454. doi:10.1093/alcalc/agh085. http://alcalc.oxfordjournals.org/cgi/content/full/39/5/450.  
  28. ^ Nils Homann, Felix Stickel, Inke R. König, Arne Jacobs, Klaus Junghanns, Monika Benesova, Detlef Schuppan, Susanne Himsel, Ina Zuber-Jerger, Claus Hellerbrand, Dieter Ludwig, Wolfgang H. Caselmann, Helmut K. Seitz Alcohol dehydrogenase 1C*1 allele is a genetic marker for alcohol-associated cancer in heavy drinkers International Journal of Cancer Volume 118, Issue 8, Pages 1998-2002
  29. ^ Chemical Summary For Acetaldehyde, US Environmental Protection Agency
  30. ^ Smoking. (2006). Encyclopædia Britannica. Accessed 27 Oct 2006.

External links








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