Potassium Permanganate from scratch

[former_chemist]

I found this little tidbit of information (1911 encyclopedia) that might be useful to someone somewhere.  I didn't find this information posted anywhere on the hive or rhodium.  I cleaned it up a good bit to make it readable, hopefully I didn't make any errors.

manganese dioxide - also called pyrolusite
  Exists naturally as pyrolusite or by heating manganese carbonate to 260°C in the presence of air and washing the residue with very dilute cold hydrochloric acid. It is a hard black solid which readily loses oxygen when strongly heated, leaving a residue of Mn₃O₄. 

potassium manganate
  Manganates. These salts are derived from manganic acid H₂MnO₄. Those of the alkali metals are prepared by fusing manganese dioxide with sodium or potassium hydroxide in the presence of air or of some oxidizing agent (nitre, potassium chlorate, ect);

 MnO₂+2KOH+O₂ ^__> K₂MnO₄+H₂O

In the absence of air the reaction proceeds slightly differently, some manganese sesquioxide being formed;

 3MnO₂ + 2KOH ^__> K₂MnO₄ + Mn₂O₃ + H₂O

The fused mass has a dark olive-green color, and dissolves in a small quantity of cold water to a green solution, which is, however, only stable in the presence of an excess of alkali. The green solution is readily converted into a pink one of permanganate by a large dilution with water, or by passing carbon dioxide through it:

3K₂MnO₄+2CO₂ ^__> 2K₂CO₃+2KMnO₄+MnO₂

potassium permanganate
  Permanganates are the salts of permanganic acid, HMnO₄. The potasssum salt, KMnO₄, may be prepared by passing chlorine or carbon dioxide through an aqueous solution of potassium manganate, or by the electrolytic oxidation of the manganate at the anode. It crystallizes in dark purple-red prisms, isomorphous with potassium perchlorate. It acts as a powerful oxidizing agent, both in acid and alkaline solution; in the first case two molecules yield five atoms of available oxygen and in the second case, three atoms:

2KMnO₄+3H₂SO₄  ^__>  K₂SO₄+2MnSO₄+3H₂O+5O;

2KMnO₄+3H₂O ^__> 2MnO₂^.H₂O+2KOH+3O.

It completely decomposes hydrogen peroxide in sulphuric acid solution

2KMnO₄+5H₂O₂ +3H₂SO₄ ^__> K₂SO₄ +2MnSO₄+8H₂O +5O₂.

It decomposes when heated to 200-240°C:

2KMnO₄  ^__>  K₂MnO₄+MnO₂+O₂;

and when warmed with hydrochloric acid it yields chlorine:

2KMnO₄+ 16HCl ^__> 2KCl +2MnCl₂+8H₂O+5Cl₂.

Additional Useful Information: MnO₂ is best freshly prepared but can be refreshed by treating with very dilute hydrochloric acid.  When fresh or refreshed it is a mild oxidizer.

MnCO₃ preparation from potassium permanganate is available at

Manganese(III) Acetate

(https://www.thevespiary.org/rhodium/Rhodium/chemistry/manganous.acetate.html)

MnCO₃ and MnO₂ are readily available.

[Lestat]

You mention when warming KMnO4 with HCl, chlorine is evolved, I actually think that might be dangerous to the newbee if he didn't expect it, I make Cl with a little KMnO4 and the 16% cold brick cleaner acid all the time and the amount of chlorine evolved is quite substantial, indeed I often have problems with a nasty brown liquid from the addition squirting out of my reaction bottles.

Is the brown liquid possibly dilute permanganic acid by any chance, it seems reasonable it would be formed, and making it this way would be preferable to using permanganic anhydride  

[former_chemist]

Yes, chlorine gas is quite dangerous.  Mixing KMnO₄ with HCl produces it vigorously.

What are the contents of the addition bottle?  The usual dark fluffy stuff I have seen when KMnO₄ is left standing tends to be MnO₂ when the solution is basic.  If the solution is acidic it is probably Mn⁺² salt of an acid.  Just about anything with a higher oxidation numbers is extremely unstable outside of the narrow neutral range.

Edit: Re-read your post ... since the solution is acidic the brown stuff is most likely MnCl₂

[methymouse]

"Edit: Re-read your post ... since the solution is acidic the brown stuff is most likely MnCl2"

Nope.  MnCl2 is light pink in solution.

And for anyone working with anything involving KMnO4--be extremely careful.  Boilovers can happen with very little warning.  Never heat a solution containing KMnO4 unless you're watching it like a hawk and can dowse the sand in your sandbath.

[Jubrail]

This seems way too much when you can get a bottle of it for $8 from the same sources as always.

[former_chemist]

MnCl₂ is probably still the major constituent if the solution is acidic.  Obviously a lot of other products can be mixed in but they won't be stable in an acidic medium.  If insufficient HCl is present the chloride won't form and the result will be MnO₂ and Mn₂O₃.

[former_chemist]

Potassium permanganate is not available everywhere or available in large quantities.  It is however easy to prepare from chemicals that are readily available.

[ApprenticeCook]

[_mu_]

Anyone who has tried to filter MnO2 through a buchnel funnel hates KMnO4 like the plague. So why bother, other than that it's a nice project for tweakers?

[abolt]

500g containers of KMnO4 for ~$25 from local chemists, may be expensive if your looking at large qty's but how much do you want? its easily sourced from chem suppliers in larger qty's if need bee, no q's asked.

Whats the big problem?


AC, check your facts before giving advice to people. _{(...and preferably do it, with this kind of info, via PM).}

Potassium Permannganate is a category 3 "illicit drug precursor" in Oz.

https://www.thevespiary.org/rhodium/Rhodium/chemistry/law/illicitdrugcode.au.pdf