The decarboxylation is a Chemical reaction during which a carbonic gas molecule (CO2) is eliminated (generally by heating) from an organic molecule carrying a grouping Carboxyle, according to the following general outline:
The synthetic interest of this reaction is to remove a grouping which can have been used as intermediary of synthesis in order to this bring back to an alkane. This reaction is more or less easy according to group R. For a simple acid (such as for example the ethanoic acid), the temperature of decarboxylation is higher than 500°C. This is thus not usable during the development of natural products, because at this temperature, the other functionalities on the products are likely to be destroyed. On the other hand, certain groupings R electro-attractile which stabilize a negative charge in alpha support this reaction. For example, the malonic acids can undergo this reaction at temperatures about 180°C.
Decarboxylation of an amino-acid
An Amino-acid has a grouping carboxyl (in red on the image) which can be decarboxylé. There exists a Enzyme décarboxylase by amino-acid. For example, the Histidine () gives the Histamine (). In the bacteria, decarboxylation takes part in the Putréfaction; the Lysine () gives the Cadavérine (), the Ornithine () gives the Putrescine ().
Beta-cetonic decarboxylation of the acidsThe decarboxylation of the acids having a function ketone is carried out on their carbon , because it can then occur a circular mechanism of transfer thanks to the hydrogen bond. The molecules undergoing this elimination are form: R-CO-CH2-COOH or: HOOC-CH2-COOH (standard malonic acid). Mechanism: . The hydrogen bond is announced in green, daplacement of doublets are indicated by the red flêches.
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