Aldehydes are easily oxidized to carboxylic acids, and this reaction is often used to prepare carboxylic acids from aldehydes. The most common oxidizing agents used for this purpose are:

- Jones reagent (CrO3 in aqueous H2SO4)

- Potassium permanganate (KMnO4) in aqueous solution

- Silver nitrate (AgNO3) in aqueous ammonia