Primary alcohols and aldehydes are oxidised to corresponding carboxylic acids with oxidising agents such as :
Acidified K2Cr2O7 and Jones reagents often give some amount of esters; therefore, neutral or alkaline KMnO4 is preferred for this purpose.
From aldehydes : Besides the above reagents, aldehydes are easily oxidised to carboxylic acids with mild oxidising agents such as Tollen's reagents.
Aromatic carboxylic acids are prepared by oxidation of alkylbenzenes with alkaline permangnate. The side chain of alkylbenzene is oxidised to -COOH irrespective of the length of the chain; the side products, however, are different depending upon the alkyl group. Take a close look at the following reactions :
Hydrolysis of nitriles with H+ or OH− as catalysts yields carboxylic acids.
One of the methods to prepare aryl nitrile is given below :
Amides on hydrolysis yield carboxylic acids.
Hydrolysis of acid chlorides yields carboxylic acids. It can be done in the following ways :
Similarly, hydrolysis of acid anhydrides yields carboxylic acids.
Hydrolysis of esters either with mineral acids or alkalies gives carboxylic acid. Acidic hydrolysis of esters directly gives carboxylic acids while the basic one gives carboxylates, which upon acidification yield carboxylic acids.
The reaction of grignard reagents with crushed dry ice (solid carbon dioxide) followed by acidification with mineral acids gives carboxylic acids.