Carboxylic acids can undergo reduction reactions. Reduction is the opposite of oxidation.

For example, ethanoic acid (CH₃COOH) can be formed by the oxidation of ethanol as shown below.

As reduction is the opposite of oxidation, it can be defined as the removal of oxygen or the addition of hydrogen to a molecule.

Carboxylic acids can also react with bases to form a salt and water in neutralisation reactions. When long chain 'fatty' acids are used, the salt formed is a soap.

For example:

sodium oxide + butanoic acid → sodium butanoate + water

potassium hydroxide + oleic acid → potassium oleate + water

copper carbonate + ethanoic acid → copper ethanoate + water + carbon dioxide