Manganese heptoxide

June 24, 2024
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At first glance, you might think that a molecule with the empirical formula Mn2O7 is an ionic, possibly crystalline, solid. But manganese heptoxide is anything but that. Rather, it’s a volatile dark red oily liquid that must be handled very carefully.

An early mention of Mn2O7 in the chemical literature was an 1894 article by G. H. Bailey of Owens College (Manchester, UK), who considered the stability of oxides in relation to what he called the “periodic law”. Bailey predicted that oxides of the general formula R2O7 (where R is an electropositive element) would be among the least stable. He was right.

In the second edition (1965) of the Handbook of Preparative Inorganic Chemistry, H. Lux reported a synthesis of Mn2O7 via the reaction of solid potassium permanganate (KMnO4) with cold concentrated sulfuric acid (H2SO4). Permanaganic acid1 (HMnO4) is produced first, followed by dehydration to its anhydride, Mn2O7.2

What makes Mn2O7 different from the typical metal oxide? The Mn–O bonds are covalent, not ionic. The bonds are similar to those within the anions pyrophosphate (P2O74–) and dichromate (Cr2O72–).

As seen in the hazard information table, Mn2O7 is nasty stuff. It decomposes slowly at ambient temperature and explodes when heated to 55 °C. When added to water, it decomposes to HMnO4. When it comes into contact with any organic substance, it causes an immediate fire.

In 1948, two C&EN letters to the editor described Mn2Oexplosions. In the first, J. R. Archer of Chicago reported that when KMnO4 and concentrated H2SO4 were combined in an undried flask, the interaction between the acid and the trace of water generated enough heat to cause the contents to explode.

In response to Archer’s letter, Austin M. Patterson of Xenia, OH, recounted that a chemist held freshly made Mn2O7 close to a light to examine it, whereupon a spontaneous explosion injured him severely. Patterson also told of an incident in which a flask with hot H2SO4 cracked, causing the acid to leak into an open container of a permanganate salt, again resulting in an explosion.

Surprisingly, there is a YouTube video on how to make Mn2O7. It strongly warns of the compound’s hazards; but it could be dangerous if viewed by someone with a destructive intent.

1. CAS Reg. No. 13465-41-3.
2. Mn2O7 in the presence of H2SO4 is a green, rather than red, oil.

Manganese heptoxide hazard information*

Hazard class**GHS code and hazard statement
Explosives, division 1.1H201—Explosive; mass explosion hazardChemical Safety Warning
Oxidizing liquids; oxidizing solids, category 1H271—May cause fire or explosion; strong oxidizerChemical Safety Warning
Skin corrosion/irritation, category 1A–1CH314—Causes severe skin burns and eye damageChemical Safety Warning
Acute toxicity, inhalation, category 1–2H330—Fatal if inhaledChemical Safety Warning

*No safety data sheets for Mn2O7 are readily available. Hazard codes are from Wikipedia.
**Globally Harmonized System (GHS) of Classification and Labeling of Chemicals. Explanation of pictograms.

Molecules from the Journals

Gallium trichloride1 (GaCl3) is a deliquescent crystalline solid that readily forms a dimer (Ga2Cl6) and dissolves in solvents ranging from water to hydrocarbons. It was first described in 1888 by Lars Fredrik Nilson* and Otto Pettersson at Uppsala University (Sweden) in an article in a series that explored the chlorides of several elements. Thirty years later, Theodore W. Richards*2, W. M. Graig, and J. Sameshima at Harvard University (Cambridge, MA) reported a new method of purifying GaCl3 by subliming it from other gallium compounds that are much less volatile.

GaCl3 has applications in catalysis, synthesis of gallium compounds, and purification of elemental gallium; but this past April, Eugene Bychkov at the University of the Littoral Opal Coast (Dunkirk, France) and colleagues there and in Japan and Russia described a new use. They used supercritical GaCl3 in the oxidative recycling of rare-earth metals, transuranium elements, platinum, pnictogens, and chalcogens. They showed that the relative amounts of the flat trigonal monomer and the tetrahedral dimer of the supercritical phase can be controlled by adjusting temperature and pressure to optimize the recycling of specific metals.

Durlobactam3 is a diazabicyclooctane β-lactamase inhibitor antibiotic developed by Entasis Therapeutics (Waltham, MA). In 2016, Entasis received a world patent for treating resistant bacterial infections with a combination of durlobactam or other β-lactamase inhibitors with sulbactam4.

In April, Robert A. Bonomo at Case Western Reserve University (Cleveland) and collaborators there and at several other institutions reported that durlobactam is a potential weapon against tuberculosis (TB). Noting that diazabicyclooctane β-lactamase inhibitors also inhibit certain peptidoglycan transpeptidases, the authors showed that durlobactam inhibits the β-lactamase and peptidoglycan transpeptidase enzymes found in the cell walls of Mycobacterium tuberculosis, the bacterium that causes TB.

1. CAS Reg. No. 13450-90-3.
2. Richards was the first American to receive the Nobel Prize in Chemistry (1914).
3. CAS Reg. No. 1467829-71-5.
4. CAS Reg. No. 68373-14-8.

Molecules from the Journals

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Manganese heptoxide
fast facts

CAS Reg. No.12057-92-0
SciFindern nameManganese oxide (Mn2O7)
Empirical formulaMn2O7
Molar mass221.87 g/mol
AppearanceDark red oil or dark green crystals
Melting point5.9 °C
Boiling point55 °C (explodes)
Water solubilityDecomposes
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