Antwain
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oxidation of primary alcohols to carboxylic acids
This has been covered in many other threads scattered all over the forum, but none of those seemed appropriate to post this.
When I get back to lab work in a few weeks I am hoping to oxidise at least 2 alcohols (isobutanol and isoamyl alcohol) to the corresponding acids. My
reagents of choice will be either K2Cr2O7 (or CrO3) or KMnO4.
Now in theory this is quite simple, I have used ethanol as a reducing agent before to reduce CrO3. However under the wrong conditions at least the
following can happen...
1) oxidation to aldehyde without oxidation to acid. This is probably more likely with CrO3.
2)Oxidation to CO2 or at least C-C bond cleavage. I saw one reference to oxidation of isobutanol leading to CO2 and acetone, which would be less than
ideal.
I would probably end up going for permanganate, however that still depends on the responses to this question. If I use that reagent, I have also seen
a reference to using it in solutions with pH of 11+, which strikes me as unintuitive. Of course it is quite possible that this is the preferred
method, as it should prevent destructive oxidation. Of course, If I have 10 times too much base, how will I isolate my acids? Neutralization then
distillation? If so then I guess obtaining them anhydrous is out of the question.
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guy
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Permanganate is good at oxidizing alcohols to their acids in alkaline pH. You just have to reacidify the solution to get the acids. I suppose you
could isolate it by extracting it with ether.
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Antwain
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Ok, so that will be Mn(VII) ----> Mn(IV).
edit - I can't count this morning it seems. Will come up with the sociometry later
Whilst it seems that MnO2 is good for oxidising alcohols to aldehydes it goes no further, so it is unlikely that MnO2 will cause bond cleavage at
respectable pH (not that I am saying it ever does).
Now, If I was to use ether to extract then I would have to be careful about the mineral acid right? If it is not in huge, massive excess then it
should stay in the aqueous layer. A slight excess may help the organic acid to stay associated and move into the ether phase...?
Do I have to worry about ether peroxides with MnO2 + acid + Et2O ?
PS. that last one may sound stupid if I don't need to worry. But my father was once sitting on a lawn when a wall blew out 2 stories above him due to
a very small amount of an ether peroxide, so I tend to be rather scared of these substances.
[Edited on 12-10-2007 by Antwain]
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The_Davster
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I would go with permanganate as well, Chromium 6+ is something I like avoiding.
What I would do:
Oxidize the alcohol under phase transfer catalysis conditions, kill any MnO2 formed with bisulfite, , be sure solution is acidic, keep organic layer,
extract salt of acid into water using a NaOH solution. Take the sodium salt to the acid however you want.
[Edited on 11-10-2007 by The_Davster]
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solo
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Quote: Originally posted by The_Davster  | I would go with permanganate as well, Chromium 6+ is something I like avoiding.
What I would do:
Oxidize the alcohol under phase transfer catalysis conditions, kill any MnO2 formed with bisulfite, , be sure solution is acidic, keep organic layer,
extract salt of acid into water using a NaOH solution. Take the sodium salt to the acid however you want.
[Edited on 11-10-2007 by The_Davster] |
....i have been working on oxidation of primary alcohols and also noted an option to bisulfite,
"When most of the alcohol is consumed,e the excess of potassium
permanganate can be optionally destroyed by adding aqueous Na2SO3 or
an excess of an alcohol such as methanol."
.....source , chapter 1, pg. 5
Oxidation of Primary Alcohols to Carboxylic Acids: A Guide to Current Common Practice (Basic Reactions in Organic Synthesis)
Gabriel Tojo, Marcos I. Fernandez
http://ifile.it/7cyv9jb/64056___oxidation.of.primary.alcohol...
It's better to die on your feet, than live on your knees....Emiliano Zapata.
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not_important
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Hypochlorite bleach plus a nickel salt as catalyst:
http://www.sciencemadness.org/talk/viewthread.php?tid=12832&...
For the alcohols/acids you intend the workup should be simple. Nickel will be a precipitate of mixed valence hydroxides/oxides and can be filtered
from the solution of product; you could always toss a little NaHCO3 in first to make sure all nickel is in the ppt. Concentrate the solution, acidify
and extract with immiscible solvent of your choice.
Besides using a small alcohol such as MeOH or EtOH to destroy excess oxidant, table sugar pr glucose or fructose syrups can be used. The products are
hydroxy-acids and possibly oxalic acid for some oxidisers, high boiling points and much more soluble in water than in organic solvents so extraction
of product is simple.
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Sedit
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I was just getting ready to link to that exact thread N_I since I have used the nitric acid method as a means on small scale to generate acetic acid
from EtOH but never really quantified anything yet just took notes on how the reaction would proceed in a test tube. With a little effort im sure I
could turn KNO3+H2SO4 and alcohol into a simple over the counter means of oxidising alcohols. The reaction pushes itself along once you get it started
and fizzes away like soda till the reaction is almost complete with no external heating. I did seem to have trouble getting it to take off with MeOH
for some reason though and I never quite figured this one out.
Knowledge is useless to useless people...
"I see a lot of patterns in our behavior as a nation that parallel a lot of other historical processes. The fall of Rome, the fall of Germany — the
fall of the ruling country, the people who think they can do whatever they want without anybody else's consent. I've seen this story
before."~Maynard James Keenan
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Jimmymajesty
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I led acetaldehyde vapors into a test tube full of cc nitric acid and cobal chloride, but annoyed by the nitrogen oxides and pour the content of the
test tube into the drain.. I am gona try it out again when I have a moment to breathe..
I also lead the actealdehyde into all kind of oxidisers that I had at hand at the moment.. but nothing special(acetic..) Maybe I should tweak the
methods just to have a chance to success, not doing them when I have 5 min to do sg in the lab..
I also heated Pt on Al2O3 catalyst chips (catalyst converter) anddropped them into a test tube full of ethanol.. also nothing acetic.. I tried out
gasoline and diesel type of converters too, but failed, however I am fully aware of the fact the the catalyst in oxidative atmosphere absorb oxygen
and the conversion of alcohols and aldehydes to CO2 and H2O is almost 100%, so I am building a setup to test them in oxigen deficient conditions.
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