myristicinaldehyde
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"Mn(V) sulfate" Woes
Based on this post (which is based on neograviton's method), I decided to attempt the preparation of this manganese species, starting with
battery-grade MnO2 and 93% H4SO4.
https://www.sciencemadness.org/whisper/viewthread.php?tid=22...
I did 2 batches- the first a crude prelim. run, to see if anything actually would happen, and then a second, more serious run.
For the "crude run", I threw ~7g MnO2 and a large excess of sulfuric acid in a beaker, and heated it at max on my hotplate with strong
stirring, with a round bottom flask to act as reflux- which worked OK for 15 minutes. After it had cooled, I was left with not the starting black
MnO2 but instead a solidified foam of chocolate brown which when crushed had some reddish flakes. Neat. I then mixed this with some more
acid and toluene in a small round bottom flask and heated gently on a steam bath to see if this would react with xylene- which it did: forming a white
sandy precipitate and the xylene layer turned yellow. I took this as a positive test for "something interesting happened"
For the more serious run, I used 25g of MnO2 and 33g of sulfuric acid (more than equimolar, but that didn't hurt before) into a roundbottom
flask using salt as a sand bath. I used a reflux condenser to control the sulfuric fumes- which worked nicely. However, this foamed up and solidified
into an unstirrable paste- adding more sulfuric acid loosed this up but not for long. The end result, while having a very similar (if wetter)
structure to the first result (a hard foam), is suspiciously close in color to the starting MnO2 and I could not find any red when crushing
the lumps.
If the second run is indeed a failure, then I would blame it on very bad stirring. Should I try again? Does anyone else have experience with this
reaction? I have a reference for the oxidation of substituted toluene with MnO2/sulfuric acid, but not for this "Mn(V) sulfate".
If we don't study the mistakes of the future we're doomed to repeat them for the first time.
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DraconicAcid
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I wouldn't try isolating many manganese sulphates made through this method. Mn(III) compounds are unstable, Mn(V) even more so.
Please remember: "Filtrate" is not a verb.
Write up your lab reports the way your instructor wants them, not the way your ex-instructor wants them.
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Melgar
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Did you use manganese dioxide from actual batteries? Because that has this oily stuff in it that could potentially be what's being oxidized in this
reaction, giving who knows what. If you want purer manganese dioxide, you can either buy it as such, or use potassium permanganate to oxidize just
about anything.
The first step in the process of learning something is admitting that you don't know it already.
I'm givin' the spam shields max power at full warp, but they just dinna have the power! We're gonna have to evacuate to new forum software!
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myristicinaldehyde
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Yup, I used battery crap. Which probably explains the results.
I took the failed second run, added yet more acid, and heated strongly for 1h so that the h2so4 was refluxing in the flask. On cooling, a whitish
crust formed on top of a solidified grey mass. Not a trace of the reddish compound. I dissolved as much as I could with water and filtered, giving a
red-pink aq. solution (which on neutralization with bicarbonate made a brownish mess with no real precipitate) and left behind what I assume to be
leftover MnO2 and graphite. The solution, on addition of bleach, produced a lovely but unfilterable (very fine) chocolate precipitate of MnO2 and some
Cl2.
The end result is that this "Mn(V) sulfate" is not easy to make- in the very first run, the one that did give a product resembling the "Mn (V)
sulfate" I let the H2SO4 boil off slowly, which I did not do for any of the other runs. It is also a *terrible* way to isolate manganese from battery
crap. The NaCl/H2SO4 method works much nicer if you want that.
In the future, I will use pure MnO2, and go from there. Lesson learned...
[Edited on 2017-6-17 by myristicinaldehyde]
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Cryolite.
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You probably can purify your manganese paste via a roundabout process. First, take your paste to manganese sulfate by one of many routes on the
Internet, then treat this with sodium carbonate to precipitate manganese carbonate. Then, take the MnCO3 paste and roast it in an oven at 300 C for 5
hours. What results is charcoal black pure manganese dioxide. While I have not tested this, the product is apparently entirely in the gamma
crystalline form, and therefore can be used to oxidize benzylic alcohols by itself.
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myristicinaldehyde
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Quote: Originally posted by Cryolite.  | | You probably can purify your manganese paste via a roundabout process. First, take your paste to manganese sulfate by one of many routes on the
Internet, then treat this with sodium carbonate to precipitate manganese carbonate. Then, take the MnCO3 paste and roast it in an oven at 300 C for 5
hours. What results is charcoal black pure manganese dioxide. While I have not tested this, the product is apparently entirely in the gamma
crystalline form, and therefore can be used to oxidize benzylic alcohols by itself. |
Thanks! I had some manganese ii carbonate from a previous run- it's baking now. Tommorow, I will test this MnO2.
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Cryolite.
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Here is the paper the carbonate route comes from. However, I must retract my claim about purity. According to the second attached paper, the mixture
of oxides is roughly MnO1.85, although the temperature of roasting is not provided and the lower valence manganese can be washed out with
nitric acid and recycled . This mixture can still probably be used as is for dissolving in sulfuric acid however-- any manganese(III) oxide will just
disproportionate in the acid to manganese sulfate and manganese dioxide.
Attachment: mno2 oxidation.pdf (566kB)
This file has been downloaded 285 times
Attachment: 19800140502_ftp.pdf (5.9MB)
This file has been downloaded 343 times
[Edited on 18-6-2017 by Cryolite.]
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AJKOER
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Per the following redox reaction, I suspect, one may attempt the creation of Mn(V):
Mn(IV) + HOCl = Mn(V) + Cl- + .OH
Citing possible support for this path (link: http://pubs.acs.org/doi/abs/10.1021/ic201430v?journalCode=in... ):
"Hypochlorous acid (HOCl) produced during turnover was found to rapidly and reversibly react with manganese(III)TDMImP to give dioxoMn(V)TDMImP and
chloride ion. The measured equilibrium constant for this reaction (Keq = 2.2 at pH 5.1) afforded a value for the oxoMn(V)/Mn(III) redox couple under
catalytic conditions (E′ = 1.35 V vs NHE)."
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myristicinaldehyde
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| Quote: Originally posted by AJKOER | Per the following redox reaction, I suspect, one may attempt the creation of Mn(V):
Mn(IV) + HOCl = Mn(V) + Cl- + .OH
Citing possible support for this path (link: http://pubs.acs.org/doi/abs/10.1021/ic201430v?journalCode=in... ):
"Hypochlorous acid (HOCl) produced during turnover was found to rapidly and reversibly react with manganese(III)TDMImP to give dioxoMn(V)TDMImP and
chloride ion. The measured equilibrium constant for this reaction (Keq = 2.2 at pH 5.1) afforded a value for the oxoMn(V)/Mn(III) redox couple under
catalytic conditions (E′ = 1.35 V vs NHE)." |
However, MnO2 in bleach gives permanganate- the solution turns purple, not blue. I would need some strong ligand to keep it stable, too- especially
considering mn(v) without the ligands described is unstable except under very high pH.
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j_sum1
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Cited from http://www.explorechem.com/manganese-redox.html
25.3.8 Manganese V
Manganese V is very hard to produce. There have been numerous attempts using reducing agents on permanganate or manganate starting points or oxidizing
manganese II or IV. Here we oxidize manganese IV oxide using only air in alkaline conditions.
1. Add 350mg of manganese dioxide and 530mg of sodium hydroxide ( a 10% excess) to a pestle and mortar and carefully grind together to form a smooth
powder.
2. Quickly transfer this powder to a TOTALLY DRY tube. Do not dither about as the powder will absorb moisture from the atmosphere quickly and water
will destroy the experiment!
3. Heat by holding the tube over a Bunsen with the lid removed. Heat for 15s then remove the tube for 15s. Repeat this until 4 minutes have passed.
Now allow the tube to cool for 1 minute. Repeat the whole of this step a further 3 times then remove and allow to cool for 4 extra minutes. At all
times make sure any steam is allowed to escape the tube and not run down the sides. Manganese V is instantly destroyed by water.
4. Watch the tube as it cools. The colour will lighten and a bright blue crust of sodium hypomanganate will have formed above the black dioxide. Where
any water has touched the tube green manganese VI will be formed instead.
12NaOH + 4MnO2 + O2 gives 4Na3MnO4 + 6H2O.
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Rhodanide
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"Dither about" well, there's something I haven't heard before.
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