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Decarboxylation

Decarboxylation is any chemical reaction in which a carboxyl group (-COOH) is split off from a compound as carbon dioxide (CO2).

Contents

Common examples

Common biosynthetic decarboxylations of amino acids to amines are:

Other decarboxylation reactions from the citric acid cycle include:

Enzymes that catalyze decarboxylations are called decarboxylases or, more formally, carboxy-lyases (EC number 4.1.1).

Heating or pyrolysis of Δ9-Tetrahydrocannabinolic acid yields the psychoactive compound Δ9-Tetrahydrocannabinol.[1]

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.[2]

In organic chemistry

In retrosynthesis, decarboxylation reactions can be considered the opposite of homologation reactions, in that the chain length becomes one carbon shorter.

Many carboxylic acids can be decarboxylated with heating. Usually the acid is suspended in a high boiling-point liquid in which the acid is insoluble/immiscible. Examples include mineral oil and glycerol, depending on the acid's polarity. After a certain temperature is reached, the carboxyl group will be removed from the acid to form the decarboxylation product and CO2. Simpler acids are not as willing to undergo decarboxylation in this manner.[3]

Occasionally, catalysts such as higher boiling-point ketones or metals, mainly copper are used in this process to obtain better yields and/or reaction time. The addition of catalytic amounts of cyclohexen-2-one has been reported to catalyze the decarboxylation of amino acids. [4] However, using such catalysts may also yield an amount of unwanted by-products.

Pyrolysis of carboxylic acids also yields the decarboxylation product, however the products formed are usually prone to undergo further thermal decomposition under those conditions.

Heating a carboxylic acid strongly with soda lime is also able to affect decarboxylation.[5] Heating the product of the malonic ester synthesis with hydrochloric acid also affords decarboxylation.[6]

Depending on the conditions of the reaction, a decarboxylation can yield anywhere from 20% to nearly quantitative yields.

Decarboxylations are especially easy for beta-keto acids due to the formation of a cyclic transition state for instance in Knoevenagel condensations. The Barton decarboxylation, Kolbe electrolysis and Hunsdiecker reaction are radical reactions. The Krapcho decarboxylation is a related decarboxylation of an ester.

See also

References

  1. ^ http://www.cannabisculture.com/articles/2794.html
  2. ^ http://www.cfsan.fda.gov/~dms/benzdata.html
  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. ^ http://www.erowid.org/archive/rhodium/chemistry/tryptophan.html, Tryptamine from Tryptophan
  5. ^ 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.  
  6. ^ "Malonic Ester Synthesis". Organic Chemistry Portal. http://www.organic-chemistry.org/namedreactions/malonic-ester-synthesis.shtm. Retrieved 2007-10-26.  







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