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

In biochemistry

Common biosynthetic decarboxylations of amino acids to amines are:

• tryptophan to tryptamine
• phenylalanine to phenylethylamine
• tyrosine to tyramine
• histidine to histamine
• serine to ethanolamine
• glutamic acid to GABA
• lysine to cadaverine
• arginine to agmatine
• ornithine to putrescine
• 5-HTP to serotonin
• L-DOPA to dopamine

Other decarboxylation reactions from the citric acid cycle include:

• pyruvate to acetyl-CoA
• oxalosuccinate to α-ketoglutarate
• α-ketoglutarate to succinyl-CoA.

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

In organic chemistry

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

Chemical decarboxylations reactions often require extensive heating in high-boiling solvents. Copper salts are often added as catalysts. Heating a carboxylic acid strongly with soda lime is also able to effect decarboxylation. Heating the product of the malonic ester synthesis with hydrochloric acid also affords decarboxylation. The addition of catalytic amounts of cyclohexen-2-one has been reported to catalyze the decarboxylation of amino acids.

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 and Hunsdiecker reaction are radical reactions.

Kolbe electrolysis — the electrolysis of salts of carboxylic acids give the decarboxylated dimer products:

CH₃COOH → CH₃COO⁻ → CH₃COO· → CH₃· + CO₂

2CH₃· → CH₃CH₃

This reaction occurs via a radical mechanism as well.

See also

• Oxidative decarboxylation

References