officescape
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ozonolysis alkene->aldehyde, used in industry?
I read an interesting paper which stated that using acetone as a solvent with a bit of water will allow for cleaving double bonds into aldehydes in
excellent yields.
Ozonolysis seems like it would have a lot of uses in synthesis but I have never seen it outside of o-chem uni classes.
I always thought it was because ozonoid intermediates are unstable but using the acetone/solvated water method allows for instant reaction to
completion, seems to be a very handy tool - does anyone know of any industrial processes/synthesis which utilize ozonolysis or is it doomed to the
land of academia?
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Sigmatropic
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Pyridine has been used as a cosolvent in a pretty much identical fashion. https://pubs.acs.org/doi/abs/10.1021/ol300617r
What do you mean doomed to the land of academia? Only on paper? Only at microscale? Gram scale?
I am aware of ozonolysis being used at gramscale but would also like to know if it has been used in process chemistry.
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officescape
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Yes, I was curious if it was used in industry at the gram scale +
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Melgar
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Well, the main issue with it is that if your ozone generator starts with just regular air, the percentage that's ozone is very small. So you need
pure oxygen for it to be a significant fraction. the other issue is that with all the air going through the system, it carries away a LOT of vapors.
Including and especially acetone.
Other than that, it does work, but mostly just takes forever.
The first step in the process of learning something is admitting that you don't know it already.
I'm givin' the spam shields max power at full warp, but they just dinna have the power! We're gonna have to evacuate to new forum software!
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clearly_not_atara
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One issue with ozone is that ozonolysis generally does not consume all of the ozone in the gas stream, so some O3 is
released to the atmosphere. (wrong, see replies) Tropospheric ozone is a greenhouse gas and an irritating pollutant:
https://en.wikipedia.org/wiki/Tropospheric_ozone#Health_effe...
Detoxifying ozone increases costs. Also ozone is not produced very efficiently even by the best method (PbO2-catalyzed electrolysis), so it's usually
(but not always!) cheaper to use something else where possible.
[Edited on 1-5-2018 by clearly_not_atara]
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Melgar
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Actually, with an ozonolysis setup, the O3 is so selective at cleaving C=C bonds that the way you tell when the reaction is done is you run it into a
solution of KI and starch. Any ozone that gets through would immediately turn it black.
The first step in the process of learning something is admitting that you don't know it already.
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Dr.Bob
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I used to run ozonolysis reactions in industry all of the time. They liked them because the reagent is made in-situ, scalable, cheap, and gentle,
with no heavy metals to deal with. The standard method is to run it in DCM at -78 C (lowers the volatility) until the reaction turns blue, then you
quench with DMS to cleave the intermediate into the aldehyde, and often just keep blowing N2 through the reaction. I did that on scales of mg to
multigram (I think up to 30 g). The DMS stinks, but is easily trapped with bleach. The ozonolysis apparatus was big and bulky, but the cost once
you had it was only electricity, so price was not bad once you have it. And many reactions only took 30-60 minutes.
If you had a symetrical alkene, even better, but most reactions were a terminal olefin that released acetaldehyde as a by product, which evaporated
away, so not too bad a byproduct. I never used acetone or pyridine as a cosolvent, but we generally followed an SOP, and DCM was liked because it
was non-flammable.
I have also done OsO4/NMO, which is nasty, toxic, and expensive. I also used Pb(OAc)4, also toxic and horrible. There are other methods, none as
easy as ozone. I vote for it. Much like industry loves swern oxidations, while they are a pain in the lab on a small scale, they are easy with
most big reactors, the temps are easy to achieve, the reagents are cheap and common in industry, and the smells easy to control with bleach. And
they are easily scalable to manufacturing scale for cheap. Try that with Dess-Martin reagent, which I happen to love on a small scale. A catalytic
Dess-Martin reaction would be a great win.
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unionised
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I'm fairly sure the industrial production of azeleic acid is based on ozonolysis of oleic acid on a tonne scale.
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