Potassium permanganate

K 1
Mn 1
O 4

Formula unit Lattice

Choose Lattice to see eight unit cells. Then drag to rotate; pinch or Ctrl + scroll to zoom. Arrow keys rotate, + − zoom, R resets.

6 atoms in one formula unit of an ionic lattice.

The drawing shows one formula unit of an ionic lattice, not a molecule; potassium permanganate has no molecular shape.

IUPAC name: potassium permanganate
Molar mass: 158.0320(60) g/mol
Atoms: 6
SMILES: [O-][Mn](=O)(=O)=O.[K+]
InChIKey: VZJVWSHVAAUDKD-UHFFFAOYSA-N
PubChem CID: 516875

Made of

K Mn O

Light barely passes through a crystal of potassium permanganate. HSDB, the Hazardous Substances Data Bank, describes dark purple or bronze-like crystals with a blue metallic lustre where light reflects from them. ChEBI (Chemical Entities of Biological Interest) files the compound as an inorganic potassium salt of permanganic acid. It is a solid of potassium ions and permanganate ions, each permanganate ion built from one manganese atom and four oxygen atoms. Its molar mass is 158.032 g/mol.

Dry, the crystals stay stable in air and light. HSDB puts their decomposition at about 240 °C, where they give off oxygen. CAMEO Chemicals calls the compound a very powerful oxidising agent, particularly in acid. Iron(II) salts, iodides, oxalates and many other substances break it down readily, HSDB notes, above all when acid is present.

Structure and bonding

In the formula-unit drawing, one potassium ion of charge +1 stands beside one permanganate ion, MnO₄⁻. Inside the permanganate ion, lines join the manganese atom to four oxygen atoms, and the ion’s −1 charge sits on one of them. No line reaches the potassium ion. The pair is one formula unit of an ionic lattice, not a particle that exists alone.

The Lattice view draws eight unit cells, each outlined, so that one ion has all its nearest neighbours in view. A single unit cell holds 4 potassium ions and 4 permanganate ions. HSDB calls the crystals orthorhombic, a system set out on the potassium hydroxide page. With Coordination on, one potassium ion stands out with its 12 nearest oxygen atoms, which belong to 7 permanganate ions and lie 2.80 to 3.46 Å away.

Those four drawn lines are not alike: three are double bonds, and the one to the charged oxygen is single. In the measured crystal structure behind the Lattice view, all four manganese–oxygen distances fall between 1.59 and 1.61 Å, within 0.02 Å of one another.

Where it turns up

Water treatment is the most common use of potassium permanganate in the United States, according to the US Environmental Protection Agency (EPA). Manganese in water can make it look black or brown, leave black stains and give it a bitter metallic taste. Permanganate, like ozone, oxidises the metal into particles that a filter then removes.

Beyond water, its uses on Haz-Map’s list run from bleaching textile fibres and skins and dyeing wood and fabrics to etching rubber and plastics and descaling steel. HSDB adds occasional ones: treating bulbs and rhizomes and dipping grafting knives. In 2019 Glacier National Park planned to use it for several weeks to neutralise rotenone in Camas Creek, below a native-fish project. Rotenone is a fish poison, used there to remove non-native trout.

Why it matters

Making it starts from ground manganese dioxide, oxidised together with potassium hydroxide to potassium manganate. Electrolysis of the manganate solution then crystallises potassium permanganate, the EPA explains. Since at least 1998 the United States has had only one known maker. US output was about 11 million kilograms in 2019. India supplied more than 90 per cent of US imports from 2015 to 2020. The EPA puts water treatment at 36.1 per cent of US consumption, wastewater at 22.8 per cent and water from oil and gas wells at 17.0 per cent.

Fish are treated with it in baths. The US Fish and Wildlife Service groups it with hydrogen peroxide and chloramine-T as strong oxidants killing small parasites, fungi, bacteria and a fish’s outermost skin cells. They oxidise organic molecules on cell surfaces until the cells die. They react so readily, though, that they are spent while seeping into tissue and do not reach deep. The same vigour lets algae, uneaten food and fish waste in a pond use it up quickly.

Properties

Properties of potassium permanganate Molar mass summed from IUPAC/CIAAW 2024 standard atomic weights; formula, atom and bond counts and PubChem's molecular weight from PubChem CID 516875.
Property	Value	Unit	Source
Formula (Hill order)	KMnO₄
Molar mass	158.0320(60) g/mol	g/mol	IUPAC/CIAAW 2024
Potassium atoms	1
Manganese atoms	1
Oxygen atoms	4
PubChem molecular weight	158.034 g/mol	g/mol	PubChem

Safety

Crystals and strong solutions of potassium permanganate are corrosive, and dilute solutions irritate the skin, eyes and airways. The crystals release potassium hydroxide on contact with water, Haz-Map notes, and the compound burns skin and stains it dark brown. Little is absorbed, so whole-body effects are uncommon, HSDB states, though Haz-Map lists liver and kidney injury after swallowing and manganese poisoning after long exposure. The PubChem Laboratory Chemical Safety Summary covers its hazards in full; the card for manganese compounds from NIOSH, the US National Institute for Occupational Safety and Health, covers workplaces.

Questions

Why does potassium permanganate turn brown?

Its colour follows its oxidising power. The US Fish and Wildlife Service describes a purple solution that turns brown as that power is used up. HSDB records that its solutions, unlike the dry crystals, are unstable: they keep best near neutral pH and lose oxygen when acidic or alkaline. They range from faint pink to deep violet.

Is potassium permanganate used in medicine?

Yes, on the skin. ChEBI's roles for it include antiseptic, disinfectant and dermatological drug, and HSDB gives its therapeutic category as a topical anti-infective. The World Health Organization's Anatomical Therapeutic Chemical (ATC) classification files it among dermatological antiseptics and disinfectants as D08AX06, and WHO's Model List of Essential Medicines includes it. The US Food and Drug Administration does not count it a low regulatory priority for animal drugs but has deferred action, as on copper sulfate, pending further study.

Is potassium permanganate dangerous?

Yes. The European Union's harmonised classification gives it the signal word Danger. Its hazard statements say that it may intensify fire as an oxidiser, is harmful if swallowed and is suspected of damaging the unborn child. It is also very toxic to aquatic life, with effects that persist. Nearly half of the company reports to the European Chemicals Agency add severe skin burns and eye damage.

How soluble is potassium permanganate?

Moderately, in water: the International Chemical Safety Card rates its solubility as moderate, with 6.4 g dissolving in 100 mL of water at 20 °C. CAMEO Chemicals lists the compound as soluble in water. Organic liquids are another matter. HSDB records potassium permanganate as soluble in acetone and in methanol, and also as decomposed by alcohol.