What are the conditions for the decarboxylation reaction? How to control the temperature of heating?

The decarboxylation of aromatic acids is easier than that of fatty acids. For example, benzoic acid can be decarboxylated by adding a little copper powder as a catalyst in quinoline solution and heating.

When a strong electron-withdrawing group is attached to the α-C of the carboxylic acid, heating can make it decarboxylate more smoothly. For example: when the ortho-diaromatic organic acid is heated, it is easy to remove a carboxyl group, but when the temperature is low, an acid anhydride will be formed. When different polycarboxylic acids are heated, according to the different activities, some are decarboxylated, some are dehydrated, some are decarboxylated and dehydrated again, dehydration above pimelic acid, and general decarboxylation below.

Fatty acid: This reaction is generally not used to prepare alkanes for general fatty acids, especially long-chain fatty acids, because the reaction temperature is too high, the yield is low, and it is not easy to separate. However, if the α-carbon atom of the fatty acid has an electron-withdrawing group such as nitro, halogen, carbonyl, cyano, etc., it makes decarboxylation easy and the yield is high, but their reaction processes are not exactly the same.

The general decarboxylation reaction does not require a special catalyst, but is carried out under the following conditions: (1) heating; (2) alkaline conditions; (3) coexistence of heating and alkaline conditions. The most commonly used decarboxylation method is to heat the sodium salt of carboxylic acid with soda lime (CaO + NaOH) or solid sodium hydroxide, and a decarboxylation reaction occurs, that is, -COONa is replaced by an H atom to generate a carbon atom less than the sodium salt of carboxylic acid alkanes.

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