Sodium permanganate (NaMnO₄) is an inorganic compound composed of sodium (Na⁺) and permanganate (MnO₄⁻) ions. It appears as a deep purple to almost black crystalline solid due to the presence of the strongly oxidizing permanganate ion. It is highly soluble in water, forming a purple solution similar to that of potassium permanganate (KMnO₄), its more common counterpart.
Sodium permanganate is a powerful oxidizing agent used in chemical synthesis, water treatment, and environmental remediation. It is closely related to the more commonly encountered potassium permanganate, but it is generally less desirable, because it is more expensive to produce. It is mainly available as the monohydrate. This salt absorbs water from the atmosphere and has a low melting point.
Preparation
Sodium permanganate cannot be prepared analogously to the route to KMnO4 because the required intermediate manganate salt, Na2MnO4, does not form. Thus less direct routes are used including conversion from KMnO4.
Sodium permanganate behaves similarly to potassium permanganate. It dissolves readily in water to give deep purple solutions, evaporation of which gives prismatic purple-black glistening crystals of the monohydrate NaMnO4·H2O. The potassium salt does not form a hydrate. Because of its hygroscopic nature, it is less useful in analytical chemistry than its potassium counterpart.
It can be prepared by the reaction of manganese dioxide with sodium hypochlorite:
2 MnO2 + 3 NaClO + 2 NaOH → 2 NaMnO4 + 3 NaCl + H2O
Properties
- Chemical formula: NaMnO4
- Molar mass: 141.9254 g/mol, 159.94 g/mol (monohydrate)
- Appearance: Red solid
- Density: 1.972 g/cm3 (monohydrate)
- Melting point: 36 °C (97 °F; 309 K) (170 °C for trihydrate)
- Solubility in water: 90 g/100 mL
Natural Occurrence
Sodium permanganate does not occur naturally; it is synthetically produced.
Synthesis: Typically made by reacting potassium permanganate (KMnO₄) with sodium-based salts in a metathesis reaction or by direct oxidation of sodium manganate in an acidic medium.
Example reaction: KMnO₄ + NaCl → NaMnO₄ + KCl
Applications
Because of its high solubility, its aqueous solutions are used as a drilled hole debris remover and etchant in printed circuitry, with a limited utility though. It is gaining popularity in water treatment for taste, odor, and zebra mussel control. It is often used in in situ chemical oxidation (ISCO) for treating contaminated soil and groundwater, especially for oxidizing organic pollutants like chlorinated solvents and hydrocarbons. It is also used in analytical chemistry, where its strong oxidative properties are valuable for redox titrations.
- Water treatment: Removes iron, manganese, hydrogen sulfide, and tastes/odors.
- Industrial cleaning: Due to strong oxidizing action.
- Chemical synthesis: Oxidizing agent in organic and inorganic reactions.
- Medical use: Occasionally used for disinfectant purposes in solution form.
Handling
Handling sodium permanganate requires caution due to its oxidative nature—it can cause fires when in contact with organic materials or reducing agents. It should be stored in a cool, dry place away from incompatible substances. Though less commonly available than potassium permanganate, sodium permanganate offers unique benefits in high-purity or specialty applications.
