Sciencemadness Discussion Board - Purifying Potassium Permanganate

Purifying Potassium Permanganate

Meltonium - 25-9-2016 at 15:49

So recently I ordered about 1.5kg of potassium permanganate off of Amazon. I read the MSDS for the product from the supplier and it says 60-100% KMnO4 with sodium sulfate contamination accounting for the majority of the other percentage. I tried to recrystallize some of it but there was a lot of MnO2 residue from the recrystallizing dish. Is there any way I can separate the Na2SO4 and the KMnO4 without a lot of decomposition?

nezza - 25-9-2016 at 23:38

Potassium permanganate is much less soluble in water than Sodium sulphate so initially I would try washing it with a few changes of slightly acidulated water (a drop of two of sulphuric acid to keep the pH down). Then you can try recrystallising it again in slightly acidulated water. KMnO4 is not very soluble in water (a couple of hundred grams per litre in hot water) so assuming you end up with 700g of KMnO4 you should try 2 or 3 l of water for the recrystallisation. Try doing these on a sample first with scaled down amounts to make sure it will work before committing the lot.

Deathunter88 - 26-9-2016 at 00:40

In my experience when an MSDS lists 60-100% of some ingredient they are purposefully being vague. If you look up some MSDS's for paint thinner some of them say "60-100% Hydrotreated light distillate (petroleum)." But really if you think about it what other thing can be part of paint thinner? So I think that the product you bought can be used as is, unless there is another reason for you to suspect high contaminations (color etc.) A link to the actual MSDS would be helpful though.

byko3y - 26-9-2016 at 03:16

If manganese dioxide precipitate is a problem, then you can just filter the solution using a sinistered glass filter.

wg48 - 26-9-2016 at 06:12

Washing with even very dilute acid is very likely to make more manganese dioxide as it would produce permanganic acid which decomposes to manganese dioxide.

Maroboduus - 26-9-2016 at 06:46

I think acetone might be your answer. Try dissolving some in a minimum of acetone filtering and evaporating.
Low solubility would require an awful lot though.
Got a Soxhlet? perhaps you could leach it out with a Soxhlet, under partial vacuum if needed.

Sodium sulphate might only be common in those permanganate products described as "free flowing' . Perhaps you can find one without this anti-caking agent in it.

Or you could even try buying an actual reagent instead of a can of green sand filter regenerator, or whatever you bought.

Depending on just what you want it for, you might not need to eliminate the sodium sulphate.

[Edited on 26-9-2016 by Maroboduus]

Maroboduus - 27-9-2016 at 12:38

Amazon also sells Black Swan permanganate, which according to the company is 97% Potassium permanganate. A 3lb bottle is around $45 US.

aga - 27-9-2016 at 13:10

Depending on intended usage, just use it as-is.

What is the intended purpose that requires it to be free of sodium suphate ?

Alternatively, buy purer material off ebay :-

http://www.ebay.co.uk/itm/100-g-Potassium-permanganate-Kaliu...

It's not expensive enough to mess about with, although messing about with things is what it's all really about.

SuperOxide - 18-1-2020 at 03:32

@Meltonium - I know this is an old thread of yours, but did you ever find a decent way to purify the KMnO₄? I just purchased 2 pounds of technical grade, looking for a good way to purify it as well.

Quote: Originally posted by Maroboduus

I think acetone might be your answer. Try dissolving some in a minimum of acetone filtering and evaporating.
Low solubility would require an awful lot though.
Got a Soxhlet? perhaps you could leach it out with a Soxhlet, under partial vacuum if needed.[Edited on 26-9-2016 by Maroboduus]

Using acetone and a soxhlet extractor seems like an interesting idea. You thinking just let the soxhlet run and eventually some purified KMnO₄ will precipitate out of the acetone in the bottom flask as it gets overly saturated? I may give this a shot

Thanks!

Sulaiman - 18-1-2020 at 04:23

Quote: Originally posted by SuperOxide

Using acetone and a soxhlet extractor seems like an interesting idea.

I could be worrying for nothing but heating acetone with potassium permanganate sounds like a potential fire bomb

unionised - 18-1-2020 at 06:21

Quote: Originally posted by Sulaiman

Quote: Originally posted by SuperOxide

Using acetone and a soxhlet extractor seems like an interesting idea.

I could be worrying for nothing but heating acetone with potassium permanganate sounds like a potential fire bomb

I second that.

Also, the OP has probably sorted it out in the intervening few years.

DavidJR - 18-1-2020 at 08:26

Quote: Originally posted by Sulaiman

Quote: Originally posted by SuperOxide

Using acetone and a soxhlet extractor seems like an interesting idea.

I could be worrying for nothing but heating acetone with potassium permanganate sounds like a potential fire bomb

I've distilled acetone from potassium permanganate before and it's fine.

unionised - 18-1-2020 at 10:30

Quote: Originally posted by DavidJR

Quote: Originally posted by Sulaiman

Quote: Originally posted by SuperOxide

Using acetone and a soxhlet extractor seems like an interesting idea.

I could be worrying for nothing but heating acetone with potassium permanganate sounds like a potential fire bomb

I've distilled acetone from potassium permanganate before and it's fine.

So have I. It's a good way to strip (some) impurities out of the acetone.
But the relevant question is "Have you distilled acetone from permanganate that contains unspecified impurities?".

BingTinsley - 4-3-2023 at 20:02

What is the answer to the OP's question?

Surely someone on the forum has figured out how to separate potassium permanganate from a powdered mixture that contains sodium sulfate.

Potassium permanganate is incompatible with alcohols and inorganic solvents, so exploitation of Na2SO4's insolubility in organics seems unlikely.

So the obvious plan B is recrystallisation, right? Heat solution of the two compounds, cool it slowly, and (due to lower solubility of pot. perm. in water) there should be nice majestic purple crystals in a few hours or the next morning...

BUT it seems to me that potassium permanganate is eagerly ready to destroy itself and degrades to manganese dioxide at any opportunity!

Does anyone have a proven method to separate KMnO4 from Na2SO4 ?

[Edited on 5-3-2023 by BingTinsley]

Keras - 5-3-2023 at 11:41

Matter of fact, I was attempting last week-end to separate KMnO₄ from KCl {I obtained potassium permanganate using oxidation of manganese dioxide with potassium hydroxide the usual way, but without extra potassium nitrate, then after dissolving the manganate in water, I used HCl to neutralise the hydroxide and cause the manganate to disproportionate}. I couldn't recrystallise it properly. Now I just think the yield was super poor (it was more a proof of concept than anything else), because KMnO₄ is much more soluble than KCl at high temp and much lower at low temp, so this makes it the perfect candidate for recrystallisation from hot water, really.

Jome - 6-3-2023 at 00:46

Potassium permanganate slowly decomposes in solutions even at room temperature, so any process involving heating a solution beyond that will destroy a lot of the product. I did the MnO2-KOH air oxidation, IIRC the yield was 11-13% (by sodium oxalate titration)

Keras - 6-3-2023 at 01:05

Quote: Originally posted by Jome

I did the MnO2-KOH air oxidation, IIRC the yield was 11-13% (by sodium oxalate titration)

Thanks for the figure.
Apparently it is possible to operate up to 65 °C. Probably the lack of any solubility data above this point is due to rapid decomposition, but 65 °C is quoted in several sources so it might be possible to raise the solution at this temperature without suffering to much loss.

teodor - 6-3-2023 at 01:55

+1 use it as it is
Purifying of permanganates/manganates is a challenging task which requires special techniques.

Keras - 13-5-2023 at 01:18

I managed to get a batch of pretty pure potassium permanganate crystals from MnO₂ using KClO₃ as oxidant during the fusion with KOH, and then by bubbling CO₂, from a simple generator made with sodium bicarbonate on which I dripped hydrochloric acid, until the solution of potassium manganate turned purple.

This procedure is different from that of (the late) Chemplayer who couldn't achieve a clean separation using KNO₃ and sodium bicarbonate.

I could probably from then have optimised the crystallisation process, but that first run was just a demo. KCl and KCO₃ are much more soluble than KMnO₄, so recrystallisation is easy. Apparently, evaporating down the permanganate solution until the first crystals appear is a viable option. Some permanganate reverts to manganese dioxide, but it doesn’t really impact the yield.

clearly_not_atara - 15-5-2023 at 07:40

https://pubs.acs.org/doi/pdf/10.1021/ed064p1058

There seems to be little awareness that sunlight catalyzes the decomposition of permanganate solutions. As do cobalt and nickel:

https://www.sciencedirect.com/science/article/abs/pii/002219...

As such it is important to consider whether you can effectively avoid sunlight, Ni and Co when attempting this purification. The decomposition is also catalysed by MnO2 itself.

Keras - 15-5-2023 at 09:36

Quote: Originally posted by clearly_not_atara

https://pubs.acs.org/doi/pdf/10.1021/ed064p1058

There seems to be little awareness that sunlight catalyzes the decomposition of permanganate solutions.

Purification of Laboratory Chemicals explicitly states that evaporation should be done in the dark. Matter of fact, I let my permanganate solution dry for 3 weeks or more on a sunlit shelf (behind windows, of course), and I’m not sure much decomposed into manganese dioxide.

Keras - 29-5-2023 at 11:57

(Partial) Result of last batch.