13.7 : Préparation des acides carboxyliques : aperçu

Carboxylic acids can be prepared by oxidizing alkenes, alkynes, aldehydes, primary alcohols, or alkylbenzenes.

When alkenes react with hot basic KMnO₄ or, undergo ozonolysis, they yield carboxylic acids.

Similarly, when alkynes are treated with concentrated KMnO₄ or, O₃ followed by H₂O treatment, they undergo oxidative cleavage to form carboxylic acids.

In the case of terminal unsaturation, CO₂ is released along with the acid that is formed.

1° alcohols and aldehydes are oxidized by strong oxidants such as Cr(VI) or Mn(VII) reagents, to generate carboxylic acids. Aldehydes can also be oxidized using mild reagents like Ag₂O .

Aromatic carboxylic acids can be prepared by oxidizing alkylbenzenes, provided at least one benzylic hydrogen is present.

Here, the alkyl group is completely oxidized to give benzoic acid.

Further, the presence of non-oxidizable substituents results in substituted aromatic acids.

Alternatively, alkylbenzenes upon ozonolysis, followed by H₂O₂ treatment, leads to the conversion of the benzene ring to the carboxyl group.