Sciencemadness Discussion Board

Extraction of Mn2O7 using CCl4?

Jor - 23-1-2010 at 13:52

I have been experimenting on this subject briefly a long time ago, as I read in an article that it is possible to extract Mn2O7 with CCl4 (from H2SO4). This is probably the only organic solvent that even is a candidate, as it has carbon in it's highest oxidation state, unlike all other solvents, wich would get oxidised. I imagine that even things like chloroform and DCM are readily oxidised to phosgene.

I did the following experiment at a temperature of about 5C.

To a small spatula (100mg?) of potassium permanganate were added about 2-2,5mL of concentrated sulfuric acid. the test tube was shaken well, and a dark green solution was obtained, with some crystals still floating around.
Now about 2mL of CCl4 were added, and the mixture was shaken for 20 seconds. This was the result:



As I read that Mn2O7 is a red compound (in CCl4 and if pure), I thought at least some dissolved in the upper layer. But no, after taking a small amount of the CCl4 and vigorously shaking it with water, the water layer remained completely colorless and not even the slightest pink was observed. When pouring the rxn mix in a beaker, there was a green oil, a brownish solution (CCl4) and some brown precitipate (MnO2?)



Now I really wonder what this brown compound is , both the precitipate and the dissolved compound. For formation of MnO2, I can only think of one way, and that is cleavage of the C-Cl bond, with formation of chlorine and phosgene. Is this possible considering the extreme reactivity of Mn2O7?
I really have no clue what the dissolved compund would be, it should be a covalent compound as it is soluble in CCl4...

Any ideas?

What other solvents would possibly be suitable for extracting such a harsh compound? I guess you would need to use inert inorganic solvents, or possibly liquid CO2, wich is ofcourse not in my interest.

woelen - 24-1-2010 at 00:49

If I look at these results then I have the strong impression that Mn2O7 hardly is soluble in CCl4. I can imagina that a very small amount of MnO2 is dispersed in the CCl4 as a solid. Very fine particles of MnO2 can form a yellow/brown colloidal solution. So, I think that this extraction does not work at all. I at least would expect a much darker CCl4 layer.

manimal - 24-1-2010 at 01:10

Maybe because it is present in solution as permanganic acid.

Fleaker - 24-1-2010 at 09:40

Jor,

This is excerpted from Brauer's:
"
Manganese (VII) Oxide
Mn2O7
2 KMnO4 + 2 H2SO4 = 2 KHSO, + Mn2O7 + H2O
316.1 196.2 272.3 221.9
Concentrated H2SO4 (15 ml., d 1.84) is placed in a dry porcellain
mortar precleaned with chromosulfuric acid; then 23 g. of
KMnO4 is carefully added over a period of 10-15 minutes, while
constantly stirring with a pestle. To obtain the desired result, the
following precautions must be observed: only very pure KMnO4
crystals, free of dust and organic substances (preferably Merck
A.R. quality; do not reduce the crystals to powder), can be used.
The reaction slurry should be left standing overnight in a dry
spot, protected against dust. Porous pyrolusite is formed during
this time, and the Mn2O7 oil is very gently kneaded out from it.
Proper safety measures must be observed during the preparation
and further workup of the material, since it often explodes for
no apparent reason (an asbestos face shield with safety glasses
and heavy leather gloves should be worn and one should work
behind heavy glass plate and a fine wire screen).
Yield: 10 g. (62%). The product is entirely free of K+ and SO4{2-}.
SYNONYMS:
Manganese heptoxide, permanganic acid anhydride.
PROPERTIES:
An oil with green metallic luster in reflected light; dark red
in transmitted light. Stable under refrigeration (—10 °C)
provided anhydrous conditions are maintained. Reacts explosively
with most organic compounds; attacks acetic acid, acetic anhydride
and CCl4 even below room temperature. Dangerous compound!
The impact sensitivity of Mn2O7 is equal to that of mercuric
fulminate."

When the editor says it is a dangerous compound, particularly in that book, it means be very, very careful!! Wear a face shield and good gloves & leather apron. I would also say double layer clothing in case any gets on and sets fire to it.

The whole synthesis works as attested, and ONLY as it is written. Make a modification at your peril; trust me when I say this! The manganese dioxide is a byproduct of the reaction--its formation occurs on standing (this MnO2 is the same as pyrolucite).

It is a green, red fuming oil. It smells much like ozone with the odor of KMnO4. I have posted some better photos of it. If you make it, I would not store it. Also, I would not work with it in the light, or humid, or hot conditions, as I have noticed it tends to explode.

I wouldn't dare (now) isolate more than 500 mg of this compound. The 10g prep in Brauer's is easily enough material to lose more than a finger, and certainly will leave horrible scars which do not go away.

Also, be aware that your MnO2 cake from which you knead the material out still contains the Mn2O7 in its matrix and may explode if dropped or left out in the light and currents of air.

The_Davster - 24-1-2010 at 11:27

http://www.sciencemadness.org/talk/viewthread.php?tid=5557#p...

Know what you are getting into, I have made and isolated this stuff a half dozen times by the Brauer method(never more than isolating around 1mL of the pure liquid), never suffering a disastrous incident, but I took every effort to work dust- and organic-free, spotless glassware. Any spillage of even a drop may either detonate or start a fire.

And you are kneading what is essentially a primary in a mortar and pestle....

In all fairness to contrast my uneventful-yet-scary experience, to how things can go wrong here... heed Fleaker's warnings!
https://www.sciencemadness.org/whisper/viewthread.php?tid=42...

[Edited on 24-1-10 by The_Davster]

Jor - 25-1-2010 at 02:23

Yes, I know how dangerous it is, I already read NERV's story on this.

As soon as the H2SO4 was added, I used the hood's sash as a safety shield at all times.

Secondly, I used a dilute solution of the Mn2O7 on purpose, so 100mg in 2-3mL H2SO4! Thought this makes it less sensitive.

Mixell - 2-2-2011 at 12:51

I mixed 4.6 grams of KMnO4 with 3 ml of concentrated sulfuric acid.
I received a black-dark red mud, and I absolutely do not know how to extract the Mn2O7 from this sludge.
Can anyone offer any help?

blogfast25 - 2-2-2011 at 14:29

Quote: Originally posted by Mixell  
I mixed 4.6 grams of KMnO4 with 3 ml of concentrated sulfuric acid.
I received a black-dark red mud, and I absolutely do not know how to extract the Mn2O7 from this sludge.
Can anyone offer any help?


BOOOM!

The_Davster - 3-2-2011 at 02:39

Quote: Originally posted by Mixell  
I mixed 4.6 grams of KMnO4 with 3 ml of concentrated sulfuric acid.
I received a black-dark red mud, and I absolutely do not know how to extract the Mn2O7 from this sludge.
Can anyone offer any help?


See what I linked to above a year ago... Both the how to, and the "how bad it can go"

Arthur Dent - 3-2-2011 at 04:27

This is one of those chemicals that serves little or no purpose and is utterly dangerous. I know that many people attempt to synthetize it just because they can, but frankly, I don't understand why do people want to generate that stuff at all. :o

Even HF is less scary than that (and I'll never get near HF, ever!)

Robert

Mixell - 3-2-2011 at 06:42

Well, it got rid of that useless mess, too much trouble and danger for basically nothing.
And blogfast (again), seriously? I expect to see this kind discussion in some teenage-hackers forum or what not, not in a chemistry forum.
And if you really want to warn me about the dangers associated with this experiment, a simple warning would be appreciated.
But if not, so "BOOM" to you too sir.

[Edited on 3-2-2011 by Mixell]

blogfast25 - 3-2-2011 at 08:36

Quote: Originally posted by Mixell  
I expect to see this kind discussion in some teenage-hackers forum or [...][Edited on 3-2-2011 by Mixell]


But a teenage-hacksters forum is exactly where you belong! You're intent on doing things you simply don't understand and with the most dangerous chemicals possible too!

When (not if) you get that BOOOOOM!, I won't even tell you 'I told you so'... Some people aren't worth engaging with.

madscientist - 3-2-2011 at 12:02

It's good to offer warnings, but your current tone needs to go - you're derailing the thread.

Don't be so quick to dismiss Jor's idea! See the attached paper. :cool:

Attachment: dimanganeseheptoxideinsolvent.pdf (361kB)
This file has been downloaded 1100 times

woelen - 3-2-2011 at 23:46

Quote: Originally posted by Mixell  
I mixed 4.6 grams of KMnO4 with 3 ml of concentrated sulfuric acid.
I received a black-dark red mud, and I absolutely do not know how to extract the Mn2O7 from this sludge.
Can anyone offer any help?
I understand your interests in energetic mixes like this, I also had (and still have) ;)

I just want to suggest that you use smaller quantities in your experiments. Don't use gram quantities. This mix of 4.6 grams of KMnO4 with 3 ml of H2SO4 could indeed have exploded and such a quantity is enough to maim yourself or have a serious fire in your house.

Limit yourself to quantities of appr. 200 mg (a pile on the tip of a medium size screw driver or small knife and a few drops of liquid). No need to use such large quantities. It adds more risk, costs more money and gives more waste.

Micro scale chemistry is the key to a long, affordable and safe home chemistry career :)

The above words apply even stronger when dealing with highly energetic materials and that is the case in your experiment.

So, keep up the experimenting and try to explore and let your curiousity lead you in your experiments, but keep safe!

Formatik - 4-2-2011 at 11:58

It's confusing that there are references saying CCl4 is alright for extraction of Mn2O7, then others are saying it reacts. The reference below says it reacts. This reference is where some saftey about the compound comes from.

It says acetic acid and even carbon tetrachloride in the cold are quickly oxidized, and that the chlorine that is generated from the CCl4 can be determined by smell and through o-tolidine.

Attachment: Mn2O7 - Z. anorg. u. allg. Ch. 1953, 271, 293.pdf (1.3MB)
This file has been downloaded 620 times

madscientist - 4-2-2011 at 12:08

I can't read German so I'm unable to comment on that.

The reference I gave mentions the reaction with solvents, and explains how to avoid it. It states the solution is stable and safe to handle, and they give a number of examples of low temperature organic oxidations.

blogfast25 - 4-2-2011 at 13:50

Quote: Originally posted by madscientist  
It's good to offer warnings, but your current tone needs to go - you're derailing the thread.

Don't be so quick to dismiss Jor's idea! See the attached paper. :cool:


I'm not dismissing Jor's idea: we know it's possible to make Mn2O7. I was addressing Mixell.

madscientist - 4-2-2011 at 18:08

I owe you an apology, my writing was unclear - I was referring to others in the thread. Sorry about that!

Mixell - 5-2-2011 at 04:11

Quote: Originally posted by woelen  
Quote: Originally posted by Mixell  
I mixed 4.6 grams of KMnO4 with 3 ml of concentrated sulfuric acid.
I received a black-dark red mud, and I absolutely do not know how to extract the Mn2O7 from this sludge.
Can anyone offer any help?
I understand your interests in energetic mixes like this, I also had (and still have) ;)

I just want to suggest that you use smaller quantities in your experiments. Don't use gram quantities. This mix of 4.6 grams of KMnO4 with 3 ml of H2SO4 could indeed have exploded and such a quantity is enough to maim yourself or have a serious fire in your house.

Limit yourself to quantities of appr. 200 mg (a pile on the tip of a medium size screw driver or small knife and a few drops of liquid). No need to use such large quantities. It adds more risk, costs more money and gives more waste.

Micro scale chemistry is the key to a long, affordable and safe home chemistry career :)

The above words apply even stronger when dealing with highly energetic materials and that is the case in your experiment.

So, keep up the experimenting and try to explore and let your curiousity lead you in your experiments, but keep safe!


Well, yes, I admit that I was way over my head in this case, need to stick to more safer alternatives, preferably compounds that have a good shock/heat resistance and offer some use outside of the usual "yay, I managed to produce it".