18.1 Carboxylic acids

Reflux a primary alcohol or aldehyde with acidified dichromate/manganate to obtain a carboxylic acid. Nitriles and esters can be hydrolysed, then an alkaline product is acidified when required.

Choose conditions from the starting functional group. Reflux keeps a primary oxidation product in the flask; hydrolysis breaks C–N or ester bonds and acidification converts the carboxylate into the free acid.

Propan-1-ol → propanoic acid under reflux. CH₃CH₂CN + 2H₂O → CH₃CH₂COOH + NH₃ after acid hydrolysis, with the atom balance checked.

Distillation isolates an aldehyde; reflux drives further oxidation to the acid. Do not leave an alkaline carboxylate when the requested product is the acid.

Carboxylic acids react with reactive metals to release H₂, with alkalis to form salt and water, and with carbonates to form salt, water and CO₂. With alcohols they esterify in concentrated sulfuric acid.

The same acid functional group supports different observations: gas evolution with metal/carbonate, neutralisation with alkali, and a reversible condensation with alcohol. Write the correct products for the reagent.

2CH₃COOH + 2Na → 2CH₃COONa + H₂; CH₃COOH + Na₂CO₃ → 2CH₃COONa + H₂O + CO₂. Ethanoic acid + ethanol ⇌ ethyl ethanoate + water.

A carboxylic acid is weak, not non-reactive; and esterification is not complete neutralisation because it is reversible.