The aldehydes will react further with (KMnO4), being oxidized to become carboxylic acids. Controlling the temperature and concentration of the reagent can keep the reaction from continuing past the formation of the glycol.
When aldehydes are reacted with potassium permanganate, they undergo oxidation, transforming into carboxylic acids. The rate of this reaction can be controlled by adjusting both the temperature and the concentration of the potassium permanganate reagent to ensure that it stops at the production of the glycol.