stephill92
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Weird Question about KMnO4
I bought some DCM from Carolina Biological to do an oxidation of nitrotoluene. I tried dissolving the KMnO4 in what I thought was DCM but it didn't
turn purple at all. Is that normal? I haven't tested the boiling point to confirm if it actually is what it's supposed to be but I've never had a
problem with a supplier sending the wrong chemical in the right package.
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Heptylene
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Maybe KMnO4 is completely insoluble in DCM? I have a hunch it's poorly soluble at best. Maybe you were thinking of iodine? It's quite soluble and
makes a purple solution too.
Measure the density and boiling point of your "DCM". You won't know unless you test it.
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Boffis
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@stephill92; who's procedure are you using? What makes you think that KMnO4 is soluble in DCM to an extent that it will colour it? Personally I doubt
it in the absence of a cationic phase transfer agent.
It is important to know what procedure/ target you are aiming at since if its nitrobenzoic acid aqueous alkali and potassium permanganate will
probablt work perfectly well inspite of the sparing solubility of nitrotoluenes in water. If, on the other hand, you are trying to produce
nitrobenzaldehydes then it might be tricky without either a PTC or a suitable co-solvent and I can't see DCM being a particularly good co-solvent in
this case.
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stephill92
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I couldn't find a procedure for oxidizing nitrotoluene to benzoic acid so I didn't know which solvent to use. I didn't think water would work since
nitrotoluenes are insoluble in them so I tried to use DCM.
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Boffis
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I think you will find that nitrotoluenes are more soluble in water than potassium permanganate in DCM  .
I haven't tried using permanganate for this procedure but there is one for dichromate in aqueous medium. There is a published procedure of
2-nitrotoluene to 2-nitrobenzoic acid using permanganate though. Check out Monnet et al, Berichte d. Chem. Ges. vol12, p443.
I have it somewhere but if I can't find it it is available free from the French web site Gallica
Ahh found it, you have to download either page by page (its only 3 pages) or the entire volume (1420 pages).
Its interesting because on a quick look through they are working on mixed isomer then seperating them as salts. But it should work with pure
nitrotoluenes too
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stephill92
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I tried looking for it and can't seem to find it. Would you happen to have a link for the procedure? Also I probably should have clarified I'm using
P-Nitrotoluene.
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Boffis
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Hi stephill92, yep Gallica can be a bit of a pain sometimes but its worth getting to know how to use it. Anyhow I clipped the appropriate pages out of
the full volume and here they are:
Attachment: On the presence of metanitrotoluene in technical nitrotoluenes Berichte v12 Monnet et al 1897 p443.pdf (215kB)
This file has been downloaded 336 times
It is unfortunately in German but you should be able to get the gist with a little help from t'internet
Also check out Richter's Organic Chemistry; Aromatic compounds volume. In my hard copy its volume 3 but the copy that is easiest to download from the
internet is an older edition and its volume 2. It gives several other references that may help including one to chromic acid mixture etc.
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stephill92
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Thanks so much, I'll read both of those.
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ZetekitoxinAB
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Permanganate is insoluble in organic solvents like benzene, DCM etc. Try to oxidize 4 nitrotoluene as a suspension in water, brought to gentle reflux
and stirring to which you add dropwise saturated permanganate.
You can dissolve KMnO4 in benzene and pretty sure in CHCl3 if you add 18 crown 6.
If you want to dissolve the nitrotoluene in an organic solvent, you could try using a 2 phase mixture with saturated permanganate solution to which
you add a PTC like 18 crown 6, benzalkonium maybe etc. I would use in this case a more inert solvent like benzene or CCl4;
Also I would try dissolving the nitrotoluene in acetone and oxidize with a saturated solution of dichromate in 20% sulfuric acid
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stephill92
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If I did it in water would I then just add sulfuric acid and filter then nitrobenzoic acid?
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Boffis
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Also bear in mind the stoichometry of the reaction which, while more complex in reality must be close to:
C7H7NO2 + 2KMnO4 -> KC7H4NO4 + 2MnO2 + KOH + H2O
This suggest that for complete oxidation you will need 2.3g of potasium permanganate per gram of nitrotoluene and so the benzoic acid will end up as
its potassium salt but there will be an excess of alkali. My experience of permanganate oxidations is that you can suspend the organic phase in water
and simply add the KMnO4 as a fine powder slowly to the well stirred mixture. Some require temperature control to keep the temperature down some
don't. The Monnet paper uses 3g of permanganate per g of nitrotoluenes.
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chemplayer...
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Never seen a purple colour from KMnO4 in a DCM layer before. It's probably just insoluble.
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stephill92
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Thanks for the reaction equation, I'll try that and see how it goes.
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S.C. Wack
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BTW Noyes has the separation of the nitrobenzoic acids in English, if anyone is interested in that sort of thing, in the different editions of Org
Chem for the Lab (which I did not scan years ago only because the library copy was too fragile). Vogel gives similar, different directions for toluene
and xylene oxidation.
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karlos³
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I did an oxidation in DCM with an aq. phase of KMnO4 and it worked fine because I used a PTC, TEBAC(triethylbenzylammonium chloride).
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