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the elimination of CO2 from the carboxyl group of carboxylic acids RCOOH. Heating such an acid with soda lime yields the hydrocarbon RH and CO2. Such carboxylic acids as cyanoacetic acid, CNCH2COOH, and malonic acid, CH2(COOH)2, lose CO2 upon simple heating. Upon treatment with concentrated H2SO4, oxalic acid yields CO, CO2, and water; formic acid yields CO2 and H2. Aromatic acids undergo decarboxylation when heated in quinoline in the presence of copper powder.
Fermentation decarboxylation plays an important part in metabolic processes. Amino acids are decarboxylated by decarboxylases, whose coenzyme is primarily phosphopyridoxal. Decarboxylation of amino acids is widespread among microorganisms, particularly the bacteria that are part of the microflora of the intestines of animals and man. Decarboxylation of a number of amino acids in animal tissues leads to formation of biogenic amines (histamine and serotonin, as well as γ-aminobutyric acid, taurine, and noradrenaline). The decarboxylation of α-keto acids is brought about by decarboxylases, whose coenzyme is thiamine pyrophosphate. The oxidation decarboxylation of pyrotartaric and α-ketoglutaric acids in animals and plants plays a large part in the Krebs cycle. In cells of microorganisms, pyrotartaric acid can be decarboxylated without access of oxygen, for example, in alcoholic fermentation.