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Acetaldehyde

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Acetaldehyde

Acetaldehyde
Lewis structure of acetaldehyde
Skeletal structure of acetaldehyde
Ball-and-stick model
Space-filling model
Names
IUPAC name
Acetaldehyde
Systematic IUPAC name
Ethanal
Other names
Acetic aldehyde
Ethyl aldehyde[1]
Identifiers
 YesY
ChEBI  YesY
ChEMBL  YesY
ChemSpider  YesY
EC number 200-836-8
Jmol-3D images Image
Image
KEGG  YesY
PubChem
RTECS number AB1925000
UNII  YesY
Properties
C2H4O
Molar mass 44.05 g·mol−1
Appearance Colourless liquid
Odor Etherial
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)
soluble
Solubility miscible with ethanol, ether, benzene, toluene, xylene, turpentine, acetone
slightly soluble in chloroform
log P -0.34
Vapor pressure 740 mmHg (20 °C)[3]
Acidity (pKa) 13.57
1.3316
Viscosity ~0.215 at 20 °C
Structure
trigonal planar (sp²) at C1
tetrahedral (sp³) at C2
2.7 D
Thermochemistry
250 J·mol−1·K−1
−166 kJ·mol−1
Hazards
Main hazards potential occupational carcinogen[4]
Safety data sheet See: data page
HMDB
GHS pictograms The flame pictogram in the Globally Harmonized System of Classification and Labelling of Chemicals (GHS)The exclamation-mark pictogram in the Globally Harmonized System of Classification and Labelling of Chemicals (GHS)The health hazard pictogram in the Globally Harmonized System of Classification and Labelling of Chemicals (GHS)[5]
H224, H319, H335, H351[5]
P210, P261, P281, P305+351+338[5]
Extremely Flammable F+ Harmful Xn Carc. Cat. 3
R-phrases R12 R36/37 R40
S-phrases (S2) S16 S33 S36/37
NFPA 704
4
2
2
Flash point −39.00 °C; −38.20 °F; 234.15 K
185.00 °C; 365.00 °F; 458.15 K
Explosive limits 4.0–60%
Lethal dose or concentration (LD, LC):
LD50 (Median dose)
1930 mg/kg (rat, oral)
13,000 ppm (rat),
17,000 ppm (hamster),
20,000 ppm (rat)[4]
US health exposure limits (NIOSH):
PEL (Permissible)
200 ppm (360 mg/m3)[3]
2000 ppm[3][4]
Related compounds
Related aldehydes
Formaldehyde
Propionaldehyde
Related compounds
Ethylene oxide
Supplementary data page
Refractive index (n),
Dielectric constantr), etc.
Thermodynamic
data
Phase behaviour
solid–liquid–gas
UV, IR, NMR, MS
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
 YesY  (: YesY/N?)

Acetaldehyde (systematic name ethanal) is an 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 by the liver enzyme alcohol dehydrogenase and may be a contributing factor to hangovers from alcohol consumption. Pathways of exposure include air, water, land, or groundwater, as well as drink and smoke.[6] Consumption of disulfiram inhibits acetaldehyde dehydrogenase, the enzyme responsible for the metabolism of acetaldehyde, thereby causing it to build up in the body.

The International Agency for Research on Cancer (IARC) has listed acetaldehyde as a Group 1 carcinogen.[7]

Contents

  • History 1
  • Production 2
    • Other methods 2.1
  • Reactions 3
    • Tautomerization of acetaldehyde to vinyl alcohol 3.1
    • Condensation reactions 3.2
    • Acetal derivatives 3.3
  • Biochemistry 4
  • Uses 5
  • Safety 6
    • Exposure limits 6.1
    • Dangers 6.2
      • Toxicity 6.2.1
      • Irritation 6.2.2
      • Carcinogenicity 6.2.3
    • Aggravating factors 6.3
      • Alzheimer's disease 6.3.1
      • Genetic conditions 6.3.2
      • Disulfiram 6.3.3
    • Sources of exposure 6.4
      • Indoor air 6.4.1
      • Outdoor air 6.4.2
      • Tobacco smoke 6.4.3
      • Cannabis smoke 6.4.4
      • Alcohol consumption 6.4.5
      • Plastics 6.4.6
  • See also 7
  • References 8
  • External links 9

History

Acetaldehyde was first observed by the Swedish pharmacist/chemist Carl Wilhelm Scheele (1774);[8] it was then investigated by the French chemists Antoine François, comte de Fourcroy and Louis Nicolas Vauquelin (1800), and the German chemists Johann Wolfgang Döbereiner (1821, 1822, 1832)[9] and Justus von Liebig (1835).[10] In 1835, Liebig named it "aldehyde";[11] the name was later altered to "acetaldehyde".[12]

Production

In 2003, global production was about 1 million tonnes. Before 1962, ethanol and acetylene were the major sources of acetaldehyde. Since then, ethylene is the dominant feedstock.[13]

The main production method is the oxidation of ethylene via the Wacker process. The process involves oxidation of ethylene using a homogeneous palladium/copper system:

2 CH2=CH2 + O2 → 2 CH3CHO

In the 1970s, the world capacity of this process, the Wacker-Hoechst direct oxidation, increased to over 2 million tonnes/year.

When smaller quantities are required, it can also be prepared by the partial oxidation of ethanol, in an exothermic reaction. This process typically is conducted over a silver catalyst at about 500–650 °C.[13]

CH3CH2OH + 1/2 O2 → CH3CHO + H2O

This method is one of the oldest routes for the industrial of preparation of acetaldehyde.

Acetaldehyde can also be produced by the hydration of acetylene, catalyzed by mercury salts. The reaction produces ethenol, which tautomerizes to acetaldehyde. This industrial route was dominant prior to the Wacker process.[14] One drawback of this process is the formation of polymerization and condensation products of acetaldehyde. Furthermore, the production of acetylene is costly and environmentally problematic. The wet oxidation process was used before the Wacker process was commercially established. Iron(III) sulfate is added to reoxidize the mercury metal to the mercury(II) salt to maintain required concentration of catalyst and, thus, avoiding direct handling of mercury. Acetylene reacts at 90–95 °C and the acetaldehyde formed is separated from water and mercury and cooled to 25–30 °C. Iron(II) sulfate is formed in the reaction and is oxidized in a separate reactor with 30% nitric acid at 95 °C. Pure acetaldehyde is obtained by fractional distillation of the aqueous solution at about 200 kPa.

Other methods

Traditionally but no longer viable economically, acetaldehyde was produced by the partial dehydrogenation of ethanol:

CH3CH2OH → CH3CHO + H2

In this endothermic process, ethanol vapor is passed at 260–290 °C over a copper-based catalyst. The process was once attractive because of the value of the hydrogen coproduct.[13]

The hydroformylation of methanol with catalysts like cobalt, nickel, or iron salts also produces acetaldehyde. This process is of no industrial importance. Similarly noncompetitive, acetaldehyde arises from synthesis gas with modest selectivity.[13]

Reactions

Like many other carbonyl compounds, acetaldehyde tautomerizes to give the enol. The enol of acetaldehyde is vinyl alcohol (IUPAC name: ethenol):

CH3CH=O \overrightarrow{\leftarrow} CH2=CHOH

The equilibrium constant is only 6×10−7 at room temperature, so that the amount of the enol in a sample of acetaldehyde is very small.[15]

Ethanal-ethenol tautomerism

Tautomerization of acetaldehyde to vinyl alcohol

At room temperature, acetaldehyde (CH3CH=O) is more stable than vinyl alcohol (CH2=CHOH) by 42.7 kJ/mol:[16]

CH2=CHOH → CH3CH=O                H298,g = –42.7 kJ/mol

This keto-enol tautomerization has a very high reaction barrier height and will therefore not occur at room temperature. Nevertheless, it was recently found that this keto-enol tautomerization can be efficiently catalyzed via photochemical process[17] or by inorganic acid catalysts (e.g. HClO4 and H2SO4).[18] These findings suggest that the keto-enol tautomerization is a viable route under atmospheric and stratospheric conditions, and have received considerable attention due to their potential atmospheric implications, since vinyl alcohol is believed to be a key intermediate in the production of organic acids in the atmosphere.[19][20]

Condensation reactions

Because of its small size and its availability as the anhydrous monomer (unlike formaldehyde), it is a common electrophile in

  • International Chemical Safety Card 0009
  • NIOSH Pocket Guide to Chemical Hazards
  • Methods for sampling and analysis
  • IARC Monograph: "Acetaldehyde"
  • Hal Kibbey, Genetic Influences on Alcohol Drinking and Alcoholism, Indiana University Research and Creative Activity, Vol. 17 no. 3.
  • United States Food and Drug Administration (FDA) information for acetaldehyde
  • Acetaldehyde production process flow sheet by ethylene oxidation method

External links

  1. ^ SciFinderScholar (accessed 4 Nov 2009). Acetaldehyde (75-07-0) Substance Detail.
  2. ^ a b Stoffdaten Acetaldehyd bei Celanese Chemicals. as of December 1999.
  3. ^ a b c
  4. ^ a b c
  5. ^ a b c Sigma-Aldrich Co., Acetaldehyde. Retrieved on 2013-07-20.
  6. ^ CHEMICALS IN THE ENVIRONMENT: ACETALDEHYDE (CAS NO. 75-07-0)
  7. ^ List of IARC Group 1 carcinogens
  8. ^ Scheele, C. W. (1774) "Om Brunsten eller Magnesia nigra och dess egenskaper" (On brown-stone or black magnesia [i.e., manganese ore] and its properties), Kungliga Svenska vetenskapsakademiens handlingar (Proceedings of the Royal Swedish Academy of Sciences), 35 : 89–116 ; 177–194. On pages 109–110, Scheele mentions that refluxing ("digesting") ethanol (Alkohol vini) with manganese dioxide (Brunsten) and either hydrochloric acid (Spirtus salis) or sulfuric acid (Spiritus Vitrioli) produces a smell like "Aether nitri" (ethanol treated with nitric acid). Later investigators realized that Scheele had produced acetaldehyde.
  9. ^ See:
    • (Döbereiner) (1821) "Neue Aether" (A new ether), Journal für Chemie und Physik, 32 : 269–270. Döbereiner names the new "ether" "Sauerstoffäther" (oxygen-ether).
    • (Döbereiner) (1822) "Döbereiner's Apparat zur Darstellung des Sauerstoffaethers" (Döbereiner's apparatus for the preparation of oxygen-ether), Journal für Chemie und Physik, 34 : 124–125.
    • Döbereiner, J. W. (1832) "Bildung des Sauerstoff-Aethers durch atmosphärische Oxidation des Alkohols" (Formation of oxy-ether by atmospheric oxidation of alcohol), Journal für Chemie und Physik, 64 : 466–468. In this paper, Döbereiner made acetaldehyde by exposing ethanol vapor to air in the presence of platinum black.
  10. ^ Brock, William H. (1997) Justus von Liebig: The Chemical Gatekeeper. Cambridge, England: Cambridge University Press, pp. 83–84.
  11. ^ Liebig, J. (1835) "Sur les produits de l'oxidation de l'alcool" (On the products of the oxidation of alcohol), Annales de Chimie et de Physique, 59 : 289–327. From p. 290: "Je le décrirai dans ce mémoire sous le nom d'aldehyde ; ce nom est formé de alcool dehydrogenatus." (I will describe it in this memoir by the name of aldehyde ; this name is formed from alcohol dehydrogenatus.)
  12. ^ The name change occurred at least as early as 1868. See, for example: Eugen F. von Gorup-Besanez, ed., Lehrbuch der organischen Chemie für den Unterricht auf Universitäten … [Textbook of Organic Chemistry for Instruction at Universities …], 3rd ed. (Braunschweig, Germany: Friedrich Vieweg und Sohn, 1868), vol. 2, p. 88.
  13. ^ a b c d e f g Eckert, Marc et al. (2007) "Acetaldehyde" in Ullmann's Encyclopedia Of Industrial Chemistry, Wiley-VCH, Weinheim. doi:10.1002/14356007.a01_031.pub2
  14. ^
  15. ^
  16. ^ Johnson, R.D. III "CCCBDB NIST Standard Reference Database". nist.gov
  17. ^
  18. ^
  19. ^
  20. ^
  21. ^ Sowin, T. J.; Melcher, L. M. (2004) ”Acetaldehyde” in Encyclopedia of Reagents for Organic Synthesis (Ed: L. Paquette), J. Wiley & Sons, New York. doi:10.1002/047084289X
  22. ^ ; .
  23. ^ ; .
  24. ^ ; .
  25. ^ ; .
  26. ^ ; .
  27. ^ ;
  28. ^ ;
  29. ^ a b
  30. ^ "Acetaldehyde". ihs.com.
  31. ^ Research and Markets ltd. "Acetaldehyde – Global Business Strategic Report".
  32. ^ a b Chemical Summary For Acetaldehyde, US Environmental Protection Agency
  33. ^ CHEMICALS IN THE ENVIRONMENT: ACETALDEHYDE (CAS NO. 75-07-0). OFFICE OF POLLUTION PREVENTION AND TOXICS, U.S. ENVIRONMENTAL PROTECTION AGENCY (August 1994)
  34. ^
  35. ^
  36. ^ p3
  37. ^ International Agency for Research on Cancer Monograph Working Group, Special Report: Policy A review of human carcinogens—Part E: tobacco, areca nut, alcohol, coal smoke, and salted fish. The Lancet 2009 10, 1033–1034.
  38. ^
  39. ^
  40. ^
  41. ^
  42. ^ Spengler, John D.; McCarthy, John F.; Samet, Jonathan M. (2000). Indoor Air Quality Handbook. New York, NY, USA: McGraw-Hill Professional Publishing. ISBN 0074455494. p 761.
  43. ^
  44. ^
  45. ^ "NIDA – Publications – NIDA Notes – Vol. 20, No. 3". drugabuse.gov.
  46. ^ Nicotine's addictive hold increases when combined with other tobacco smoke chemicals, UCI study finds. University of California. 2004-10-28
  47. ^
  48. ^ Stacy, Kelli Miller (23 June 2009). "Marijuana Smoke Linked to Cancer." WebMD.
  49. ^
  50. ^ Scientific Committee on Consumer Safety SCCS OPINION ON Acetaldehyde. European Commission. 18 September 2012
  51. ^
  52. ^

References

See also

Acetaldehyde is also created by thermal degradation or ultraviolet photo-degradation of some thermoplastic polymers during of after manufacture. One common example occurs when a bottle of water is left in a hot car for a few hours on a hot, sunny day, and one notices its strange sweet taste in the water from the breakdown of the polyethylene terephthalate (PETE) container.[51] The water industry generally recognizes 20–40 ppb as the taste/odor threshold for acetaldehyde. The level at which an average consumer could detect acetaldehyde is still considerably lower than any toxic amount.[52]

Plastics

Many microbes produce acetaldehyde from ethanol, but they have a lower capacity to eliminate the acetaldehyde, which can lead to the accumulation of acetaldehyde in saliva, stomach acid, and intestinal contents. Fermented food and many alcoholic beverages can also contain significant amounts of acetaldehyde. Acetaldehyde, derived from mucosal or microbial oxidation of ethanol, tobacco smoke, and diet, appears to act as a cumulative carcinogen in the upper digestive tract of humans.[49] According to European Commission's Scientific Committee on Consumer Safety's (SCCS) "Opinion on Acetaldehyde" (2012) the cosmetic products special risk limit is 5 mg/l and acetaldehyde should not be used in mouth-washing products.[50]

Alcohol consumption

Acetaldehyde has been found in cannabis smoke. This finding emerged through the use of new chemical techniques that demonstrated the acetaldehyde present was causing DNA damage in laboratory settings.[48]

Cannabis smoke

Acetaldehyde can also be found in e-cigarette vapour, though this is reported to be trace amounts.[47]

Acetaldehyde is a significant constituent of tobacco smoke. It has been demonstrated to have a synergistic effect with nicotine in rodent models of addiction.[45][46] Acetaldehyde is also the most abundant carcinogen in tobacco smoke; it is dissolved into the saliva while smoking.

Tobacco smoke

The use of acetaldehyde is widespread in different industries, and it may be released into waste water or the air during production, use, transportation and storage. Sources of acetaldehyde include fuel combustion emissions from stationary internal combustion engines and power plants that burn fossil fuels, wood, or trash, oil and gas extraction, refineries, cement kilns, lumber and wood mills and paper mills. Acetaldehyde is also present in automobile and diesel exhaust.[44]

Outdoor air

It has been concluded that VOCs such as benzene, formaldehyde, acetaldehyde, toluene, and xylenes have to be considered as priority pollutants with respect to their health effects. It has been pointed that in renovated or completely new buildings, the VOCs concentration levels are often several orders of magnitude higher. The main sources of acetaldehydes in homes include building materials, laminate, linoleum, wooden varnished, and cork/pine flooring. It is also found in plastic water-based and matt emulsion paints, in wood ceilings, and wooden, particle-board, plywood, pine wood, and chipboard furniture.[43]

In a study in France, the mean indoor concentration of acetaldehydes measured in 16 homes was approximately seven times higher than the outside acetaldehyde concentration. The living room had a mean of 18.1±17.5 μg m−3 and the bedroom was 18.2±16.9 μg m−3, whereas the outdoor air had a mean concentration of 2.3±2.6 μg m−3.

Acetaldehyde is common contaminant in workplace, indoors, and ambient environments. It is also a potential carcinogen. Moreover, humans spend more than 90% of their time in indoor environments, hence increasing any exposure and, as a consequence, the risk to human health.[42]

Indoor air

Sources of exposure

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

Disulfiram

A study of 818 heavy drinkers found that those exposed to more acetaldehyde than normal through a defect in the gene for acetaldehyde dehydrogenase are at greater risk of developing cancers of the upper gastrointestinal tract and liver.[41]

Genetic conditions

People with a genetic deficiency for the enzyme responsible 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] …"[40]

Alzheimer's disease

Aggravating factors

Acetaldehyde is carcinogen in humans.[32][35] In 1988 the International Agency for Research on Cancer stated, "There is sufficient evidence for the carcinogenicity of acetaldehyde (the major metabolite of ethanol) in experimental animals."[36] In October 2009 the International Agency for Research on Cancer updated the classification of acetaldehyde stating that acetaldehyde included in and generated endogenously from alcoholic beverages is a Group I human carcinogen.[37] In addition, acetaldehyde is damaging to DNA[38] and causes abnormal muscle development as it binds to proteins.[39]

Carcinogenicity

Acetaldehyde is an irritant of the skin, eyes, mucous membranes, throat, and respiratory tract. This occurs at concentrations up to 1000 ppm. Symptoms of exposure to this compound include nausea, vomiting, headache. These symptoms may not happen immediately. The perception limit of acetaldehyde in air is in the range between 0.07 and 0.25 ppm.[13] At such concentrations, the fruity odor of acetaldehyde is apparent. Conjunctival irritations have been observed after a 15-minute exposure to concentrations of 25 and 50 ppm, but transient conjunctivitis and irritation of the respiratory tract have been reported after exposure to 200 ppm acetaldehyde for 15 minutes. It has a general narcotic action and large doses can even cause death by respiratory paralysis. It may also cause drowsiness, delirium, hallucinations, and loss of intelligence. Exposure may also cause severe damage to the mouth, throat, and stomach; accumulation of fluid in the lungs, chronic respiratory disease, kidney and liver damage, throat irritation, dizziness, reddening, and swelling of the skin.

Irritation

Acetaldehyde is toxic when applied externally for prolonged periods, an irritant, and a probable carcinogen.[32] Acetaldehyde naturally breaks down in the human body[33] but has been shown to excrete in urine of rats.[34]

Toxicity

Dangers

[13] The

Exposure limits

Safety

China is the largest consumer of acetaldehyde in the world, accounting for almost half of global consumption in 2012. Major use has been the production of acetic acid. Other uses such as pyridines and pentaerythritol are expected to grow faster than acetic acid, but the volumes are not large enough to offset the decline in acetic acid. As a consequence, overall acetaldehyde consumption in China may grow slightly at 1.6% per year through 2018. Western Europe is the second-largest consumer of acetaldehyde worldwide, accounting for 20% of world consumption in 2012. As with China, the Western European acetaldehyde market is expected to increase only very slightly at 1% per year during 2012–2018. However, Japan could emerge as a potential consumer for acetaldehyde in next five years due to newfound use in commercial production of butadiene. The supply of butadiene has been volatile in Japan and the rest of Asia. This should provide the much needed boost to the flat market, as of 2013.[31]

Product USA Mexico W. Europe Japan Total
Acetic Acid/Acetic anhydride - 11 89 47 147
Acetate esters 35 8 54 224 321
Pentaerythritol 26 43 11 80
Pyridine and pyridine bases 73 10 * 83
Peracetic acid 23 * 23
1,3-Butylene glycol 14 * 14
Others 5 3 10 80 98
Total 176 22 206 362 766
(* Included in others -glyoxal/glyoxalic acid, crotonaldehyde, lactic acid, n-butanol, 2-ethylhexanol)

Consumption of acetaldehyde (103 t) in 2003[13]

Production Of Acetaldehyde

Global market for acetaldehyde is declining. Demand has been impacted by changes in the production of plasticizer alcohols, which has shifted from n-butyraldehyde based on acetaldehyde to hydroformylation of propylene. Likewise, acetic acid, once produced from acetaldehyde, is made predominantly by the lower-cost methanol carbonylation process.[30] The impact on demand has led to increase in prices and thus slowdown in the market.

Traditionally, acetaldehyde was mainly used as a precursor to acetic acid. This application has declined because acetic acid is made more efficiently from methanol by the Monsanto and Cativa processes. In terms of condensation reactions, acetaldehyde is an important precursor to pyridine derivatives, pentaerythritol, and crotonaldehyde. Urea and acetaldehyde combine to give a useful resin. Acetic anhydride reacts with acetaldehyde to give ethylidene diacetate, a precursor to vinyl acetate, which is used to produce polyvinyl acetate.

Uses

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.[29] In the brain, alcohol dehydrogenase has a minor role in the oxidation of ethanol to acetaldehyde. Instead, primarily the enzyme catalase oxidizes ethanol to acetaldehyde.[29] The last steps of alcoholic fermentation in bacteria, plants, and yeast involve the conversion of pyruvate into acetaldehyde and carbon dioxide 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.

Biochemistry

Acetaldehyde forms a stable acetal upon reaction with ethanol under conditions that favor dehydration. The product, CH3CH(OCH2CH3)2, is in fact called "acetal".[28] although acetal is used more widely to describe other compounds with the formula RCH(OR')2

Three molecules of acetaldehyde condense to form “paraldehyde,” a cyclic trimer containing C-O single bonds. The condensation of four molecules of acetaldehyde give the cyclic molecule called metaldehyde.

Acetal derivatives

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”).[27]

In a Strecker reaction, acetaldehyde condenses with cyanide and ammonia to give, after hydrolysis, the amino acid alanine.[25] 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.[26]

[24].4OH)2, C(CHpentaerythritol add to MeCHO to give formaldehyde In one of the more spectacular condensation reactions, three equivalents of [23]

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