Sciencemadness Discussion Board

Reduction of KMnO4

guy - 4-6-2005 at 23:00

When KMnO4 (dry) is reduced by glycerin it forms Mn2O3, BUT what hapens when you reduce KMnO4(solution) with glycerin? I tried it and it turned red. What is complete reaction?

Really

chloric1 - 5-6-2005 at 07:02

That sounds cool. any precipitate? HOw intense is the red? Add a drop of 3% H2O2 to see if there is a MnO2 deposit.

Pyridinium - 5-6-2005 at 07:34

That could be a complex one with multiple species in equilibria, maybe even some polymeric components as well.

Might be worth it to do some digging through the literature to see if anyone's analyzed the system. Sounds very interesting.

guy - 5-6-2005 at 12:09

It is a dark red color. Adding H2O2 does precipitate MnO2.

Can someone who has these materials try this and report their results?
Just add glycerine in to a solution of KMnO4.

[Edited on 6/5/2005 by guy]

[Edited on 6/5/2005 by guy]

S.C. Wack - 5-6-2005 at 14:05

Asstalking guess: the color is Mn+3 some acid. The oxalate seems reasonable and manganic oxalate solutions are a lovely dark red. Don't know about the other acids.

guy - 5-6-2005 at 14:37

Is it possible that the glycerin could somehow have been oxidized to an organic acid, since it is an alcohol, and then formed a complex with the manganese ion?

Borek - 5-6-2005 at 14:45

Glycerine has complexing ability by itself, so there is no need for oxidation products. Which doesn't mean they are not taking part in complexation.

guy - 5-6-2005 at 15:31

I forgot to say that after a while the red color disappears and MnO2 is left.

Could this be the process? I am not sure at all, this may look stupid but its the best i can do.

KMnO4 + C3H8O3 --> C3H6O4 + KMnO3 + H2O --> K3Mn(C3H5O4)6 --> K2CO3 + MnO2

[Edited on 6/6/2005 by guy]

12AX7 - 5-6-2005 at 15:40

Manganese manganate? :o :P

I wonder if the MnO2 is from atmospheric oxygen (since H2O2 ppt's it immediately), perhaps see if it changes at all while sealed?

Oh, could plain manganate be produced? But I don't remember if that's red.

Tim

[Edited on 5-6-2005 by 12AX7]

guy - 5-6-2005 at 16:14

When KMnO4 is in Basic soloution, it turns green.
Wht is the reaction? K2MnO4?

On adding glycerin, it turns orange. What is responsible for this color?

[Edited on 6/6/2005 by guy]

[Edited on 6/6/2005 by guy]

Pyridinium - 5-6-2005 at 18:59

Quote:
Originally posted by 12AX7
Manganese manganate? :o :P

I wonder if the MnO2 is from atmospheric oxygen (since H2O2 ppt's it immediately), perhaps see if it changes at all while sealed?

Oh, could plain manganate be produced? But I don't remember if that's red.


S.C.W. might be right. The fact that the red color isn't stable is interesting. I'd be curious to see if sulfate ion stabilized the color for a longer time. Then again, the oxalate itself is supposed to make Mn(III) stable... so maybe that's what you're seeing.

I'm still thinking there's multiple oxidation states in that solution. Even without atmospheric O2, you will get MnO2 after a while, via catalytic breakdown. Small amount of MnO2 causes a positive feedback cycle, making more MnO2, etc.

Funny that in the case of (per)manganate, H2O2 acts as a reducing agent.

Also, manganate (VI) is a teal color (blue green) and is stable only in alkaline soln.

Experiment

MadHatter - 5-6-2005 at 20:44

Guy, sounds like have a series of reactions taking place. I have the materials you
mentioned so I'll try this one out for myself and post back.

More Colors!

guy - 5-6-2005 at 21:03

I never knew I could do so much with KMnO4.
KMnO4 - violet , add glycerine - red

Making the solution basic gives:

K2MnO4-Green, add glycerine or isopropyl alcohol - orange.
or
K2MnO4-Green, add NaHCO3 - hot pink
or
K2MnO4-green, add KCl - light orange.

I DON'T KNOW WHAT THESE COMPOUNDS ARE THOUGH. Does someone know the reactions.

I don't have any sulfites, but my book said it will reduce manganates to hypomanganates - Blue.

[Edited on 6/6/2005 by guy]

Pyridinium - 6-6-2005 at 15:15

Sulfite will reduce, but sulfate should stabilize Mn(III). Same with acetate. I just did some reading and found that with acetate you may get:
[Mn3O(OAc)6](OAc)(HOAc)

Apparently you can produce a hydrous form with glacial HOAc, and the anhydrous form with acetic anhydride. I don't know how stable this Mn acetate is.

I hadn't known this either, but apparently there are plant enzymes which have Mn(III) as a stable component. They are purplish in color.

Edit: by the way, Mn(III) is a pretty strong oxidizer itself.

[Edited on 6-6-2005 by Pyridinium]

guy - 6-6-2005 at 15:43

I just did a rxn with KMnO4 and NaOAc and got a red color. It lasted for about 30-45mins and its starting to precipitate MnO2.

I am a fish - 9-6-2005 at 13:28

I recently tried making hypomanganates by reducing dilute potassium permanganate solution with sodium sulphite solution. However, I merely obtained a dark brown precipitate (presumably MnO<sub>2</sub>;) and a colourless supernatant. I then repeated the experiment, but this time, I added the sodium sulphite far more slowly. Initially, I obtained a blood-red solution. However, following the addition of more sodium sulphite, I then obtained the previously mentioned brown precipitate.

I presume that the red stuff is a manganese(V) (or possibly a manganese(VI) ) compound, which is readily reduced to the manganese(IV) state.

guy - 9-6-2005 at 14:16

This is what my chem. dictionary said

Manganates(V) (hypomanganates), [MnO4]3-. Deep blue ion (MnO2 in conc. KOH; [MnO4]- plus excess [SO3]2-). The salts are rapidly hydrolysed.

I am a fish - 10-6-2005 at 00:03

I'm moving this thread from "Beginnings" to "General Chemistry".