World Library  
Flag as Inappropriate
Email this Article

Decarboxylation

Article Id: WHEBN0000193461
Reproduction Date:

Title: Decarboxylation  
Author: World Heritage Encyclopedia
Language: English
Subject: Aldol condensation, Pyruvate dehydrogenase, Azomethine ylide, Tyramine, Phosphatidylethanolamine
Collection: Substitution Reactions
Publisher: World Heritage Encyclopedia
Publication
Date:
 

Decarboxylation

Decarboxylation

Decarboxylation is a chemical reaction that removes a carboxyl group and 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 carboxylation, 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 1
    • Protodecarboxylation 1.1
  • In biochemistry 2
  • Case studies 3
  • References 4

In organic chemistry

The term "decarboxylation" literally means removal of the COOH (carboxyl group) and its replacement with a proton. The term simply relates the state of the reactant and product. 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-Barton decarboxylation, Kolbe electrolysis, Kochi reaction and Hunsdiecker reaction are radical reactions. The Krapcho decarboxylation is a related decarboxylation of an ester. In ketonic decarboxylation a carboxylic acid is converted to a ketone.

Protodecarboxylation

Protodecarboxylations involve the conversion of a carboxylic acid to the corresponding hydrocarbon. This is conceptually the same as the more general term "decarboxylation" as defined above except that it specifically requires that the carboxyl group is, as expected, replaced by a proton. The reaction is especially common in conjunction with the malonic ester synthesis and Knoevenagel condensations. The reaction involves the conjugate base of the carboxl group, a carboxylate ion, and an unsaturated receptor of electron density, such as a protonated carbonyl group. Where reactions entail heating the carboxylic acid with concentrated hydrochloric acid such a direct route is impossible as it would produce protonated carbon dioxide. In these cases, the reaction is likely to occur by initial addition of water and a proton.[5]

In biochemistry

Common biosynthetic oxidative 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] The addition of catalytic amounts of cyclohexenone has been reported to catalyze the decarboxylation of amino acids.[8] However, using such catalysts may also yield an amount of unwanted by-products.

References

  1. ^ Richard H. Wiley and Newton R. Smith. "m-Nitrostyrene".  
  2. ^  
  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. Retrieved 2007-10-22. 
  5. ^ "Malonic Ester Synthesis". Organic Chemistry Portal. Retrieved 2007-10-26. 
  6. ^ "Does marijuana have to be heated to become psychoactive?". 
  7. ^ http://www.cfsan.fda.gov/~dms/benzdata.html
  8. ^ http://www.erowid.org/archive/rhodium/chemistry/tryptophan.html Tryptamine from Tryptophan
This article was sourced from Creative Commons Attribution-ShareAlike License; additional terms may apply. World Heritage Encyclopedia content is assembled from numerous content providers, Open Access Publishing, and in compliance with The Fair Access to Science and Technology Research Act (FASTR), Wikimedia Foundation, Inc., Public Library of Science, The Encyclopedia of Life, Open Book Publishers (OBP), PubMed, U.S. National Library of Medicine, National Center for Biotechnology Information, U.S. National Library of Medicine, National Institutes of Health (NIH), U.S. Department of Health & Human Services, and USA.gov, which sources content from all federal, state, local, tribal, and territorial government publication portals (.gov, .mil, .edu). Funding for USA.gov and content contributors is made possible from the U.S. Congress, E-Government Act of 2002.
 
Crowd sourced content that is contributed to World Heritage Encyclopedia is peer reviewed and edited by our editorial staff to ensure quality scholarly research articles.
 
By using this site, you agree to the Terms of Use and Privacy Policy. World Heritage Encyclopedia™ is a registered trademark of the World Public Library Association, a non-profit organization.
 


Copyright © World Library Foundation. All rights reserved. eBooks from Project Gutenberg are sponsored by the World Library Foundation,
a 501c(4) Member's Support Non-Profit Organization, and is NOT affiliated with any governmental agency or department.