What Is Potassium Permanganate?
Potassium permanganate is an inorganic compound with the chemical formula KMnO4 and a molecular weight of 158.03. It has a density of 2.703 g/cm3, a decomposition point of 200°C, and a CAS number of 7722-64-7. This compound consists of potassium ions and permanganate ions.
The manganese in permanganate ion has an oxidation number of +7, making it a potent oxidizing agent. Classified as a hazardous substance under the Fire Service Law and as a toxic substance under the Industrial Safety Law, it must be labeled properly.
Uses of Potassium Permanganate
Known for its strong oxidizing properties, potassium permanganate is used in metal surface treatment, purification of acids, and tanker cleaning. In organic chemistry, it facilitates oxidation reactions, such as converting alcohols to ketones and aldehydes, cleaving alkenes to diols, and transforming alkyl groups on aromatic rings to carboxy groups. It also serves as a coloring reagent for TLC.
Additionally, it acts as an antiseptic and disinfectant, and is used in water purification and sewage treatment, reflecting its versatility in inhibiting microorganism growth and as a standard solution for redox titration.
Properties of Potassium Permanganate
At room temperature and pressure, potassium permanganate appears as purplish-black or greenish-black columnar rectangular crystals with a metallic luster, turning into a dark purplish-red solution when dissolved in water. It is highly soluble in water, slightly soluble in organic solvents like methanol and acetone, and in sulfuric acid, but decomposes in alcohol.
As one of the strongest oxidizers, it exhibits potent oxidation capabilities in both acidic and basic solutions. In acidic environments, it reduces to the light pink Mn2+ ion, while in basic solutions, it forms manganese dioxide (MnO2), a brown precipitate.
Other Information on Potassium Permanganate
1. Production Process
The production of potassium permanganate involves melting manganese dioxide with KOH or K2CO3 and air oxidizing in a resistant container, or mixing with an oxidant like potassium chlorate for oxidation. After cooling, the synthesized potassium manganate is dissolved in water, filtered to remove impurities, and then treated with carbon dioxide to precipitate potassium permanganate, with potassium carbonate as a byproduct.
2. Hazards
Adding potassium permanganate to alcohol can cause a violent exothermic reaction, potentially melting containers or igniting combustible materials. It is crucial to avoid flammable materials and be cautious of oxidation and hazardous substance release. Mixing with concentrated sulfuric acid can produce explosive manganese oxide (Mn2O7), and adding hydrochloric acid to a concentrated solution or solid form generates toxic chlorine gas.