nb198
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How to do KMno4 oxidation workup?
I am oxidizing 1-butanol to butyric acid using KMno4. My reaction seemed to work but I have excess kmno4 in solution. Likely something like 0.02mol
extra. 0.056 mol of butanol was used. The butyric acid is in its sodium salt form. Solvent is water. Sodium carbonate was added to neutralize the
butyric acid
How can I work this up? I obviously need to filter off the mno2, but i should destroy the excess kmno4. There are several ways I can do this, but
which one would you recommend?
Sodium thiosulfate? An alcohol? H2o2? I feel like dilute h2o2 could work or super dilute sodium thiosulfate. Alcohols oxidation products will be way
too hard to separate.
I have little experice with kmno4
[Edited on 18-5-2014 by nb198]
From what I found, sodium thiosulfate might be the best.
[Edited on 18-5-2014 by nb198]
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Zyklon-A
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Just use hydrogen peroxide. It will contaminate it less.
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blogfast25
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Assuming you're in alkaline conditions, hydrogen peroxide will reduce KMnO4 to MnO2, IIRW.
But even after filtering you're not out of the woods yet. How do you plan to isolate the butyric acid (assuming that is your goal)? Acidifying will
liberate the acid which should then separate out (it's only slightly soluble in water), so a separation funnel should do it.
I hope you realise just how vile this stuff stinks... paradoxically it does make some real fruity short chain esters.
[Edited on 18-5-2014 by blogfast25]
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nb198
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Quote: Originally posted by blogfast25  | Assuming you're in alkaline conditions, hydrogen peroxide will reduce KMnO4 to MnO2, IIRW.
But even after filtering you're not out of the woods yet. How do you plan to isolate the butyric acid (assuming that is your goal)? Acidifying will
liberate the acid which should then separate out (it's only slightly soluble in water), so a separation funnel should do it.
I hope you realise just how vile this stuff stinks... paradoxically it does make some real fruity short chain esters.
[Edited on 18-5-2014 by blogfast25] |
I just got stuck and the killing the KMno4 stage. I will then filter off the MnO2, evaporate on a hot water bath to reduce the volume, acidify, then
extract it 3-4 times with diethyl ether. I just didn't know if it was a good idea or not to use H2O2. I have never does any synthesis using KMno4
before, so I was/am really unsure.
I plan to make some nice non-stinky esters out of it.
I have made it before. I used a really roundabout way though. I brominated 1-propanol and then did a grignard with CO2. My yield was horrible, but I
was left with about 0.5mL of the acid. I ran the H-NMR and it was clean. Weirdly enough, I don't think it stinks that bad. I can smell the
concentrated stuff and it just smells like an acid. More dilute, it smells barfy, but it isn't really bad. Just something I wouldn't want on my hands
or clothing. Maybe i am just not very sensitive to it.
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mnick12
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Depending on how pure you need your acid to be, I would distill the final product after acidification. T
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Nicodem
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Thread Moved
18-5-2014 at 10:30 |
Etaoin Shrdlu
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| Quote: Originally posted by nb198 | | Weirdly enough, I don't think it stinks that bad. I can smell the concentrated stuff and it just smells like an acid. More dilute, it smells barfy,
but it isn't really bad. Just something I wouldn't want on my hands or clothing. Maybe i am just not very sensitive to it. |
That's exactly the way I feel about it. I got a bottle in to make esters with and was actually afraid to open the external packaging after what I'd
heard about the smell, and the payoff when I opened the bottle itself was a letdown. It just smells like a carboxylic acid. Like really, really
aromatic cheese or rancid butter, maybe. I'm surprised people use it as a "weapon."
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blogfast25
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Rancid butter contains small amounts of it of course. Maybe its reputation is overblown... interesting.
[Edited on 19-5-2014 by blogfast25]
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aga
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Tatteifraiche.
Now there is a Cheese to fear.
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Oscilllator
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Maybe some people are genetically predisposed to smell it, like with cyanide. My chemistry teacher opened a jar of it for me to sniff, and the smell
was so bad I nearly vomited
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phlogiston
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Same here. It's not pleasant, but it does not smell extremely bad to me either, certainly not worse than other short chain acids.
Some other compounds are much, much worse. I really dislike primary amines (cadaverine, putresceine, TEMED), sulfides/thio comounds, and some alkynes.
-----
"If a rocket goes up, who cares where it comes down, that's not my concern said Wernher von Braun" - Tom Lehrer |
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nb198
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Well, I decided to use sodium thiosulfate to neutralize the KMno4. It worked great and cleared everything up nicely.
Then I went to regenerate the butyric acid from its salt...and that is when I facepalmed. So much sulfur popped out of solution. Oops.
So, H2O2 is 100% definitely the way to go and the way that I should have gone. I have no idea how it didn't occur to me that this would happen. For
some reason in my mind once neutralized, there was no excess sodium thiosulfate.
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