Chemical Forums
Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: curiouscat on September 23, 2013, 07:28:03 AM
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What are good solvents for KMnO4 to be used as an oxidizing agent? My substrate is a water immiscible liquid and the idea is to see if reaction rates can be hastened by using an organic dissolved KMnO4 (as opposed to a water solution).
KMnO4 seems unstable in many typical solvents.
Ideas?
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Try a phase transfer catalyst and stir like hell.
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Get a crown ether like 18-crown-6, quadternatery ammonium salt, and some benzene/pyridine solvent (derivatives also work) and mix them all together. Add your KMnO4 right after, and stir. It should completely dissolve.
You never used crown ethers in your entire life? That's disappointing.
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You never used crown ethers in your entire life? That's disappointing.
Sadly true.
But thanks for the tips.
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Try a phase transfer catalyst and stir like hell.
Thanks @disco!
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I think crown ethers may be too expensive for curious, and too toxic. I think he is really large scale!
Phase transfer cats. are certainly cheaper and easier for him to handle.
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I think crown ethers may be too expensive for curious, and too toxic. I think he is really large scale!
Phase transfer cats. are certainly cheaper and easier for him to handle.
My bad. Yes, @disco brings up an important point that I always forget to mention:
This isn't a lab prep but an intended commercial process with target volumes of several tens of tons per month of a not-very-high-value product (~$5-7 / kg).
So, yeah, can't really go for very fancy / nasty or expensive ingredients.
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Several tons per month, now that is a decent scale!
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Several tons per month, now that is a decent scale!
tens of tons.... ;)
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Even better, tons is small scale stuff.
At least you see what you get, more than can be said for the poor Academics with their mgs!
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At least you see what you get, more than can be said for the poor Academics with their mgs!
One reason I switched tracks after my post doc. :)
Most of the stuff I do is quite low brow science not of any fundamental interest though.
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Must be of interest to someone with tens of tons a month.
Anyway high or low brow it's still interesting and each has its own particular problems.
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Must be of interest to someone with tens of tons a month.
Anyway high or low brow it's still interesting and each has its own particular problems.
True! Thanks for your tips as always. I'm going to try some TBAB / Aliquat. Might be challenging finding a PTC that KMnO4 won't oxidize away.
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May make TBAB permanganate?
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-18-crown-6 solvates the potassium ion in KMnO4 while the quad. ammo. salt solvates the MnO4- anion, basically.
If the crown ether is that expensive, then don't buy it. (My recommendation) Instead, why not make some yourself? You could use Williamsom ether synthesis, though chances are there will be multiple products.
Toxicity can be handled with some antidote (if possible), some PPE, and a fume hood. In factories people carry around hydrofluoric acid while whistling, and people almost never get hurt. Why so afraid of crown ethers?
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-18-crown-6 solvates the potassium ion in KMnO4 while the quad. ammo. salt solvates the MnO4- anion, basically.
If the crown ether is that expensive, then don't buy it. (My recommendation) Instead, why not make some yourself? You could use Williamsom ether synthesis, though chances are there will be multiple products.
Toxicity can be handled with some antidote (if possible), some PPE, and a fume hood. In factories people carry around hydrofluoric acid while whistling, and people almost never get hurt. Why so afraid of crown ethers?
If he is making tens of tons a month then he is using very large amounts of catalyst, just take it on a weight basis for an estimate: if the cat is 10% then that is 1 ton of 18-crown-6. Not you can't weigh that out in a fume hood. I am not aware of an antidote for 18-C-6. You need a complete body suit to handle this stuff, with separate air supply, so it is not to be trivialised.
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I used water spiked with pyridine. Worst smell ever.
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This isn't a lab prep but an intended commercial process with target volumes of several tens of tons per month of a not-very-high-value product (~$5-7 / kg).
just my 2 cents: with KMnO4 going at ~ 30$ /kg , and the volumes involved, it might be worthwhile to look into some catalyst / air, oxygen system instead....
regards
Ingo
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Using an air/oxygen mix on this scale may be problematic, you'd have to keep it under the explosion limit and then then reaction may not work due to the dilution with nitrogen.
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This isn't a lab prep but an intended commercial process with target volumes of several tens of tons per month of a not-very-high-value product (~$5-7 / kg).
just my 2 cents: with KMnO4 going at ~ 30$ /kg ,
Are you sure it is so expensive? I was expecting (just intuitively) around $5 /kg; bulk grades. I could be wrong. I'll check again.
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that would be ballpark bulk prices in Europe, based on 100 kgs / shipment CF RoAn
If, however, you became a real huge consumer (like: 100 metric tons/year) and if you imported from, let's say India, you'd significantly would reduce prices down to approx. 1500 euro / metric ton (approx 1 US-$ per pound)
... but: is your production really that huge?
different countries, different connections, different grades, different amounts...
regards
Ingo
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that would be ballpark bulk prices in Europe, based on 100 kgs / shipment CF RoAn
If, however, you became a real huge consumer (like: 100 metric tons/year) and if you imported from, let's say India, you'd significantly would reduce prices down to approx. 1500 euro / metric ton (approx 1 US-$ per pound)
Yes, $1-3 / lb sounds more reasonable to me. It is a bulk chemical after all.
I did a quick estimate and I think we'll end up using not quite 100 tons / year but say 20-30 tons I think.
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They really do rip you off for small orders; that's a 15x price markup we see, and 100 kgs is not that small a quantity after all! ;D
I cringe to see how much Sigma will charge for a kg or two. Probably a 100x markup on bulk prices. ::)
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Sigma in Europe goes at approx 100 Euro / kg (~ 62 US-$/lb , 1 kg single order)
http://www.sigmaaldrich.com/catalog/product/sial/223468?lang=de®ion=DE
... at that's about the level for other lab-suppliers in general here, too
regards
Ingo
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As a supplementary question:
For a KMnO4 oxidation is it necessary / recommended to acidify the reagent? I'm trying to oxidize benzaldehyde. Often I see H2SO4 added for KMnO4 based oxidations.
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the oxidation potential of MnO4- is highly pH- dependant: with slightly alkaline to ~ neutral conditions you'll end up with MnO2 :spindown: , i.e. 3 electrons per permanganate , under acid conditions with Mn2+(aq.) (i.e. 5 electrons per permanganate)
"acid" to the best of my knowledge means pH < 3
regards
Ingo