Chemical Properties and Reactions of Sodium Permanganate
Sodium permanganate (NaMnO4) is a dark purple crystalline solid known for its powerful oxidizing properties. It is a highly soluble compound comprising sodium (Na+) and permanganate (MnO4–) ions that create a deep purple solution when dissolved in water.
Due to its strong oxidizing properties, sodium permanganate plays a crucial role in various industries as an oxidizing agent and disinfectant. In particular, it is used as a reagent for In Situ Chemical Oxidation (ISCO) processes because of its versatility and effectiveness in eliminating pollutants like chlorides, nitrates, organic compounds, and heavy metals.
Learn more about the chemical properties of sodium permanganate and its chemical reactions below.
Chemical Properties of Sodium Permanganate
Below are some of the chemical properties of sodium permanganate:
Sodium permanganate is a highly reactive compound stemming from the high oxidation state of manganese (+7) in the permanganate ion (MnO4−), which gives it its strong oxidizing nature. As a powerful oxidizing agent, it readily participates in reduction-oxidation (redox) reactions as an electron acceptor, oxidizing a wide range of substances, including organic compounds and heavy metals.
Sodium permanganate itself is not combustible. However, it can accelerate the burning of combustible materials when heated or involved in a fire due to its strong oxidizing nature. It can also decompose explosively when heated or react explosively with hydrocarbon fuels.
The aqueous solution of sodium permanganate is alkaline. First, sodium permanganate dissociates into sodium (Na+) and MnO4–, which then reacts with water molecules to produce hydroxide ions (OH–). This is represented by reactions (1) and (2):
(1) NaMnO4 (solid) + H2O (liquid) → Na+ (aq) + MnO4− (aq)
(2) MnO4− (aq) + 2H2O (liquid) → MnO2 (solid) + 4OH− (aq)
The exact pH of the resulting solution will depend on the concentration of the solution.
Solid sodium permanganate is generally stable in ambient environments (around 20-25°C or 68-77°F). However, when exposed to elevated temperatures, it undergoes decomposition, leading to the formation of sodium manganate (Na2MnO4), manganese(III) oxide (Mn2O3), and the release of oxygen gas (O2). This process is represented by reaction (3):
(3) 6NaMnO4 → 5Na2MnO4 + Mn2O3 + 3O2
Potassium permanganate solutions are generally only available as 1-5% solutions because of the low solubility of potassium permanganate (KMnO4). With water kept heated above 65 degrees fahrenheit, a 6% solution is possible, though this is not generally feasible in most uses. In contrast, sodium permanganate is soluble up to 40%, making it readily available in solutions at higher concentrations.
Due to its hygroscopic nature, proper storage is always important when dealing with sodium permanganate. This refers to its ability to absorb water vapor from the atmosphere. When exposed to humid air, sodium permanganate powder:
- Increases in weight
- Transforms from a dry, crystalline solid to a wet or damp state
- Clumps together due to caking
All of these can affect its physical state and handling characteristics. However, proper storage conditions, including humidity control, can help minimize the effects of hygroscopicity.
For these and other reasons, outside of specialized uses, sodium permanganate is broadly available only in liquid form.
At high concentrations, sodium permanganate is considered highly corrosive, especially to the skin and eyes. Exposure may lead to irritation, burns, or tissue damage.
If contact occurs, it is crucial to immediately flush the affected area with copious amounts of water for at least 15 minutes. Remove contaminated clothing and seek medical attention promptly. Proper protective gear, including gloves and safety goggles, should be worn when handling sodium permanganate to prevent direct contact and minimize the potential for skin and eye injuries.
Sodium permanganate is highly toxic and has been classified as “harmful if swallowed.” Animal studies have confirmed that the harmful effects of oral exposure can be severe, emphasizing the need for caution while handling this chemical. Similar studies have also shown its toxicity in aquatic environments, making it dangerous to the environment.
However, because of its strong oxidizing nature, its persistence in the environment may be short-lived as it readily converts to insoluble manganese oxide in the presence of oxidizable materials. Nevertheless, the toxic potential of sodium permanganate still demands that proper handling measures be taken to prevent exposure.
Reactions of Sodium Permanganate
Sodium permanganate is widely used for soil and groundwater remediation through ISCO. As a strong oxidizing agent, it facilitates the breakdown of various contaminants, which is represented in the following chemical reactions:
(4) NaMnO4 + C2Cl4 → MnO2 + CO2 + 2NaCl
In the treatment of chlorinated ethenes (tetrachloroethylene or perchloroethylene -TCE or PCE- in the above example), sodium permanganate acts as a strong oxidizing agent, facilitating the oxidative degradation of the target substance.
In this reaction, sodium permanganate replaces chlorine atoms in PCE, producing manganese dioxide (MnO2), carbon dioxide (CO2), and two moles of sodium chloride (NaCl). The reduction of manganese in sodium permanganate forms manganese dioxide, while dechlorination of PCE releases carbon dioxide.
This remediation process mitigates environmental contamination, transforming harmful chlorinated ethenes into less hazardous byproducts and preventing their spread in groundwater and soil.
(5) NaMnO4 + C6H4(OH)2 → MnO2 + CO2 + 2H2O + NaOH
The above example shows the oxidation of the phenolic compound hydroquinone C6H4(OH)2. In this reaction, sodium permanganate replaces hydrogen atoms in the phenolic ring, oxidizing the compound to form manganese dioxide, carbon dioxide, two moles of water (H2O), and sodium hydroxide (NaOH).
The reduction of manganese in sodium permanganate results in manganese dioxide, while the phenolic compound releases carbon dioxide. This process helps to break down phenolic pollutants and convert them into less harmful substances, thereby reducing environmental risks.
Polyaromatic Hydrocarbons (PAHs)
(6) 6NaMnO4 + C10H8 → 6MnO2 + 2CO2 + 8H2O + 6NaOH
During the oxidation process, sodium permanganate is reduced to form manganese dioxide. Simultaneously, naphthalene is oxidized to produce carbon dioxide, water, and sodium hydroxide. This remediation reaction transforms naphthalene, a PAH pollutant, into less harmful byproducts, mitigating its environmental impact and aiding in the cleanup of contaminated sites.
The reaction between RDX and sodium permanganate is an important environmental remediation process in sites contaminated with residue from explosives. RDX, more commonly known as cyclonite, is a cyclic nitramine explosive and is oxidized by sodium permanganate during this process, represented by reaction (7):
(7) 10NaMnO4 + 2C3H6N6O6 → 10MnO2 + 6CO2 + 3H2O + 5NaOH + 6N2
Sodium permanganate oxidizes RDX and breaks it down into carbon dioxide, water, nitrogen gas (N2), sodium hydroxide, and manganese dioxide. This process helps to degrade the complex structure of RDX, resulting in less harmful byproducts. The formation of manganese dioxide confirms the reduction of manganese in sodium permanganate.
HMX is a colorless solid that explodes violently at high temperatures. Also known as octogen, it is used in various kinds of explosives, rocket fuels, and burster chargers because of its explosive nature. It is also formed as a byproduct in the production of RDX, although in small amounts.
The chemical reaction between sodium permanganate and HMX during environmental remediation is represented by reaction (8):
(8) 9NaMnO4 + 2C4H8N8O8 → 9MnO2 + 8CO2 + 10H2O + 5NaOH + 4N2
The reaction shown above involves the oxidation of HMX by sodium permanganate, forming several byproducts, such as manganese dioxide, carbon dioxide, water, sodium hydroxide, and nitrogen gas. This process breaks down the complex structure of HMX, leading to the formation of less harmful byproducts.
Find Effective Environmental Remediation Solutions at CAP Remediation
Sodium permanganate is one of the most versatile reagents used in the in situ remediation of soil and groundwater systems. However, while it may effectively remove a wide range of contaminants, as shown in the above reactions, other reagents may be more suitable for other applications.
CAP Remediation supplies a wide range of remediation-grade chemical reagents that promote the effectiveness of your environmental remediation projects while preserving the integrity of the environment. Browse our list to find the products you need. You are also welcome to get in touch with us to learn more about how we can help support your projects today!