Decarboxylation

Decarboxylation
Decarboxylation

Decarboxylation is a chemical reaction that releases carbon dioxide (CO2). Usually, decarboxylation refers to a reaction of carboxylic acids, removing a carbon atom from a carbon chain. The reverse process, which is the first chemical step in photosynthesis, is called carbonation, the addition of CO2 to a compound. Enzymes that catalyze decarboxylations are called decarboxylases or, the more formal term, carboxy-lyases (EC number 4.1.1).

Contents

In organic chemistry

Decarboxylation is one of the oldest organic reactions, since it often entails simple pyrolysis, and volatile products distill from the reactor. Heating is required because the reaction is less favorable at low temperatures. Yields are highly sensitive to conditions. In retrosynthesis, decarboxylation reactions can be considered the opposite of homologation reactions, in that the chain length becomes one carbon shorter. Metals, especially copper compounds,[1] are usually required. Such reactions proceed via the intermediacy of metal carboxylate complexes.

Decarboxylation of aryl carboxylates can generate the equivalent of the corresponding aryl anion, which in turn can undergo cross coupling reactions.

Alkylcarboxylic acids and their salts do not always undergo decarboxylation readily.[2][3] Exceptions are the decarboxylation of beta-keto acids, α,β-unsaturated acids, and α-phenyl, α-nitro, and α-cyanoacids. Such reactions are accelerated due to the stabilization of the cyclic transition state. To generate the carboxylate salts for decarboxylation, the parent carboxylic acid is heated strongly with soda lime.[4] Typically fatty acids do not decarboxylate readily.


Named decarboxylation reactions

Many reactions have been named after early workers in organic chemistry. The Barton decarboxylation, Kolbe electrolysis and Hunsdiecker reaction are radical reactions. The Krapcho decarboxylation is a related decarboxylation of an ester.

Protodecarboxylation

Protodecarboxylations involve the conversion of a carboxylic acid to the corresponding hydrocarbon. This reaction is especially common in conjunction with the malonic ester synthesis and Knoevenagel condensations. Many such reactions entail heating the carboxylic acid with concentrated hydrochloric acid.[5]

Common biochemical examples

Common biosynthetic decarboxylations of amino acids to amines are:

Other decarboxylation reactions from the citric acid cycle include:

Case studies

Upon heating, Δ9-Tetrahydrocannabinolic acid decarboxylates to give the psychoactive compound Δ9-Tetrahydrocannabinol.[6]

In beverages stored for long periods, very small amounts of benzene may form from benzoic acid by decarboxylation catalyzed by the presence of vitamin C.[7]

See also

References

  1. ^ Richard H. Wiley and Newton R. Smith, "m-Nitrostyrene", Org. Synth., http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=cv4p0731 ; Coll. Vol. 4: 731 
  2. ^ March, Jerry (1985), Advanced Organic Chemistry: Reactions, Mechanisms, and Structure (3rd ed.), New York: Wiley, ISBN 0-471-85472-7 
  3. ^ http://www.chem.ucalgary.ca/courses/350/Carey5th/Ch19/ch19-3-4.html, Decarboxylation, Dr. Ian A. Hunt, Department of Chemistry, University of Calgary
  4. ^ Jim Clark (2004). "The Decarboxylation of Carboxylic Acids and their Salts". Chemguide. http://www.chemguide.co.uk/organicprops/acids/decarbox.html. Retrieved 2007-10-22. 
  5. ^ "Malonic Ester Synthesis". Organic Chemistry Portal. http://www.organic-chemistry.org/namedreactions/malonic-ester-synthesis.shtm. Retrieved 2007-10-26. 
  6. ^ http://www.cannabisculture.com/articles/2794.html
  7. ^ http://www.cfsan.fda.gov/~dms/benzdata.html

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См. также в других словарях:

  • Decarboxylation — Décarboxylation La décarboxylation est une réaction chimique au cours de laquelle une molécule de dioxyde de carbone (CO2) est éliminée (généralement par chauffage) d une molécule organique portant un groupement carboxyle, selon le schéma général …   Wikipédia en Français

  • décarboxylation — [ dekarbɔksilasjɔ̃ ] n. f. • 1911; de dé et carboxyle ♦ Chim. Perte d un ou de plusieurs groupes carboxyliques provenant d un composé organique. Biochim. Cette action chimique catalysée par une enzyme. ● décarboxylation nom féminin Réaction au… …   Encyclopédie Universelle

  • decarboxylation — decarboxylation. См. декарбоксилирование. (Источник: «Англо русский толковый словарь генетических терминов». Арефьев В.А., Лисовенко Л.А., Москва: Изд во ВНИРО, 1995 г.) …   Молекулярная биология и генетика. Толковый словарь.

  • decarboxylation — [dē΄kär΄bäk΄si lā′shən] n. 〚 DE + CARBOXYL + ATION〛 the removal or loss of a carboxyl group from an organic compound, as amino acid, usually resulting in the formation of carbon dioxide decarboxylate vt., vi …   Universalium

  • decarboxylation — [dē΄kär΄bäk΄si lā′shən] n. [ DE + CARBOXYL + ATION] the removal or loss of a carboxyl group from an organic compound, as amino acid, usually resulting in the formation of carbon dioxide decarboxylate vt., vi. decarboxylated, decarboxylating …   English World dictionary

  • Décarboxylation — La décarboxylation est une réaction chimique au cours de laquelle une molécule de dioxyde de carbone (CO2) est éliminée (généralement par chauffage) d une molécule organique portant un groupement carboxyle, selon le schéma général suivant :… …   Wikipédia en Français

  • decarboxylation — dekarboksilinimas statusas T sritis chemija apibrėžtis CO₂ atskėlimas iš HOOC– grupės. atitikmenys: angl. decarboxylation rus. декарбоксилирование …   Chemijos terminų aiškinamasis žodynas

  • decarboxylation — noun Date: 1922 the removal or elimination of carboxyl from a molecule • decarboxylate transitive verb …   New Collegiate Dictionary

  • decarboxylation — noun The removal of one or more carboxyl groups from a molecule See Also: decarboxylate …   Wiktionary

  • decarboxylation — A reaction involving the removal of a molecule of carbon dioxide from a carboxylic acid. oxidative d. d. requiring the participation of coenzymes such as NAD+, NADP+, FAD, or FMN. * * * de·car·box·y·la·tion (de″kahr bok″sə… …   Medical dictionary


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