Sciencemadness Discussion Board

KMnO4 > MnO2 + HNO3 > Mn(NO3)X

bolbol - 25-1-2015 at 23:40

Hi everyone

I have two questions regarding the synthesis of manganese nitrate that I want to do.

I have some potassium permanganate laying around so I thought of making a Manganese salt with it.

I want to decompose the KMnO4 to MnO2 but I am not sure if there is any easy way to do that. I know the H2O2 method but that would require tons of bottles since I cant get my hands on concentrated stuff and i would probably have gallons of liquid to filter off which is just messy..
I also know that heating it will decompose too but I have never attempted it a larger scale so I don't know if its really safe to do so.

Then theres the reaction of MnO2 with Nitric acid. I believe there is no Mn(NO3)4 compound so if Im correct then Im guessing it gets reduced to Mn(NO3)2?

DJF90 - 26-1-2015 at 00:07

Treat the permanganate with stoichoimetric MnSO4. The MnO2 that forms is particularly active for the oxidation of allylic/benzylic alcohols to the corresponding aldehydes/ketones.

bolbol - 26-1-2015 at 00:19

Unfortunately I don't have MnSO4 to begin with and In fact I don't have that kind of stuff around.
Somewhere else someone said to make an alkaline solution and treat it with a reducing agent like sugar or ethanol, but he didn't really go into detail on how exactly I could make an alkaline solution with it

woelen - 26-1-2015 at 04:24

Dissolve some KMnO4 in water, make it as concentrated as possible.
Add this solution to a solution of sugar, to which also some NaOH is added. Soon, MnO2 settles at the bottom. Let the liquid stand for one day, I expect a dark brown precipitate to settle at the bottom and having a clear solution above it.

Use 1 teaspoon of sugar, half a teaspoon of NaOH and add half a teaspoon of KMnO4, dissolved in water.

MnO2 does not form Mn(NO3)2 with HNO3 though. You also need some reductor. I would try oxalic acid, which is completely oxidized to CO2 and then evaporate the liquid to get Mn(NO3)2. I do not expect an easy separation, Mn(NO3)2 is very hygroscopic and I am afraid you will have a hard time getting dry crystals.

bolbol - 26-1-2015 at 14:15

So are u saying MnO2 wouldn't react with nitric acid at all?

bolbol - 26-1-2015 at 16:43

Alright so I did it in two different ways to see the difference.

For experiment #1
-Dissolved 6 grams of KMnO4 in 200 mls of water.
-Then I added 6 grams of NaOH in it.
-After all was dissolved, I added around 50 mls of 91% isopropyl alcohol

the solution immediately turned a nice green color and then after a while turned into a brown goo... resembling the color of.. well u know what

For experiment #2
-Dissolved 1 gram of KMnO4 in around 50 mls of Acetone (Not all of it dissolved)
-Added 100 mls of water to the mixture
-Added 1 gram of NaOH

The solution turned a dark color, probably dark brown couldnt really tell, but after a while I noticed the solution was clear and I could see what I think is the MnO2 particles all over the place.


I've added H2O2 to permanganate before and the resulting solution resembled what I got out of experiment #2.

Whats wrong with #1? are there any water insoluble impurities or should I let the solutions sit for a while

woelen - 26-1-2015 at 23:34

Particles of MnO2 can be very fine and it may be hard to isolate it. Boiling a solution for a while may help, it makes precipitates coarser and easier to filter.

MnO2 will not react with dilute HNO3, with more conc. HNO3 I also doubt that there will be any reaction. Keep in mind that for the MnO2 to turn into a manganese(II) salt, you need a reductor and with HNO3 only you don't have that. Adding oxalic acid to MnO2 suspended in dilute nitric acid certainly will lead to reduction of the MnO2, but with HNO3 alone you won't get Mn(NO3)2.

bolbol - 26-1-2015 at 23:44

Theres a difference in color of the product that occured which im not sure if its due to the particle size or contaminates but with isopropyl method my product was brown and with Acetone and H2O2 the product was a much darker brown.

And yes I understand, I will try hot conc HNO3 with MnO2 tho just to confirm that there wont be a reaction

AJKOER - 27-1-2015 at 06:14

You may consider looking at dry cell batteries as a source for MnO2. To quote from Wikipedia http://en.m.wikipedia.org/wiki/Battery_(electricity)#Dry_cell :

"A standard dry cell comprises a zinc anode, usually in the form of a cylindrical pot, with a carbon cathode in the form of a central rod. The electrolyte is ammonium chloride in the form of a paste next to the zinc anode. The remaining space between the electrolyte and carbon cathode is taken up by a second paste consisting of ammonium chloride and manganese dioxide, the latter acting as a depolariser. In some designs, the ammonium chloride is replaced by zinc chloride."
-------------------------------

Note the following reaction path:

MnO2 + 4 HCl → Cl2 (g) + 2 H2O + MnCl2 [edit correction]

MnCl2 + 2 AgNO3 →2 AgCl (s) + Mn(NO3)2

For the dry salt, unsure if two moles of moist NO2 acting on MnO2 works (see http://www.sciencedirect.com/science/article/pii/S0925400511... and this educational reference site https://www.google.com/url?sa=t&source=web&rct=j&... ).

I will let others comment on feasibility.

[Edited on 27-1-2015 by AJKOER]

blogfast25 - 27-1-2015 at 07:43

Quote: Originally posted by AJKOER  
Note the following reaction path:

MnO2 + 4 HCl → Cl2 (g) + 2 H2O

MnCl2 + 2 AgNO3 →2 AgCl (s) + Mn(NO3)2



AJ and the case of the magically disappearing manganese!

Don't waste silver nitrate on this. Instead precipitate the MnCl2 as MnCO3(s) with Na2CO3 solution. Filter, wash and dry carefully.

MnCO3 is a very stable, slightly pink solid. It does not oxidise to MnO2 easily.

Dissolve it in any relevant dilute acid (including HNO3) to obtain the relevant Mn(II) salt.

[Edited on 27-1-2015 by blogfast25]

AJKOER - 27-1-2015 at 09:21

Yes, and the accidental deletion has been corrected via the magical edit function;).

I also added an unknown educational link which actual cites my direct action by NO2 on MnO2 forming the nitrate.

The accidental formation of dry Al(NO3)3 via NO2 was, per recollection, once reported on SM as well. Interestingly, as Aluminum/Al2O3 does resist direct attack by HNO3 to form a nitrate, Aluminum and Manganese oxide may behave similarly with NO2.

[Edit] Found the thread here http://www.sciencemadness.org/talk/viewthread.php?tid=22790 shown below:
Quote: Originally posted by Antiswat  

[/rquote]
What I found interesting was that anhydrous aluminum nitrate can be prepared from AlCl3 in N2O4 at 0 °C.

[Edited on 23-12-2012 by AndersHoveland][/rquote]

A bit off topic, but when ive made Pb(NO3)2 by HNO3 + Pb i have covered my flask with 10 layers of aluminium foil, and apparently the NO2 formed can and WILL react with the aluminium foil to make aluminium nitrate, infact this reaction is probably taking place right now, just thought its weird that aluminium wont react with HNO3 but NO2 reacts with aluminium


Here is also a general reference thanks to Wikipedia on NO2, to quote:

"Conversion to nitrates

NO2 is used to generate anhydrous metal nitrates from the oxides:[6]

MO + 3 NO2 → M(NO3)2 + NO"

Because NO2 is toxic upon inhalation of small quantities, I would recommend working with NO and O2 passed through broken glass (in the ratio of 2 to 1 which is the cited method enabling mixing of gases and NO2 formation ) brought into contact with the MnO2.

One preparation for NO, not even requiring HNO3 is:

2KNO3 + 6FeCl2 + 8HCl→ 2KCl + 6FeCl3 + 2NO + 4H2O
---------------------------------------------------------

With respect to aqueous methods, one can replace the expensive AgNO3 with say Pb(NO3)2, assuming the Lead toxicity is not an issue.

[Edited on 27-1-2015 by AJKOER]