Chemical Forums
Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: curiouscat on August 07, 2014, 12:52:47 PM
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I saw a protocol for a hydroxylation reaction that uses H2O2 as the reagent to introduce an -OH group at the ortho / para position on a aromatic ring. Some of the original patents do the reaction in water and the others use dioxane (depending on what molecule is the substrate).
But one variation mentions acetone as a solvent. I was wondering, is it safe to add H2O2 to a medium containing acetone predominantly? The regular flamabality hazards of Acetone are understood but is there a explosion hazard? Triacetone triperoxide? Has anyone done reactions involving addition of H2O2 to acetone? Intuitively adding H2O2 to solvents sounded like an iffy operation.
The H2O2 will be approx. 30% and the reaction calls for a temperature of ~60 to 70 C (at reflux). The initial reaction mixture has ~75% acetone.
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Acetone and peroxide are a dangerous combination especially when heated. I believe the compound formed is dioxirane. Better stick to the Sandmeyer reaction for OH introduction.
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I seem to recall that this mix was what triggered the TSA prohibition on liquids greater than 3 oz on airplanes, so probably pretty powerful explosive !!
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Acetone and peroxide are a dangerous combination especially when heated. I believe the compound formed is dioxirane. Better stick to the Sandmeyer reaction for OH introduction.
Thanks! This is intended for a commercial synthesis at scale so the attractiveness of the H2O2 route is huge. It is single step, fairly cheap and innocuous reagent, no nasty by products, reported yields not too bad (though I have to verify), acetone is easy to flash off and recycle etc.
Instead of ditching the H2O2 route what about swapping the solvent? Ideas? What would be safer (yet cheap, not too nasty) alternatives to using acetone for this particular reaction?
Original patent mentions "acetone, methanol, acetonitrile, t-butanol and dioxane" but they may have been only going for the breadth of their claims.
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Well I would not use any of these. What about an ester, t-butyl acetate or similar?
Make it bulky enough and you should avoid ester hydrolysis and any "Bayer-Villiger" type of chemistry.
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Well I would not use any of these. What about an ester, t-butyl acetate or similar?
Make it bulky enough and you should avoid ester hydrolysis and any "Bayer-Villiger" type of chemistry.
Thanks! I'll try what you suggest.
Out of curiosity, what was the reasoning you used to reject all the others. Not a hard reason perhaps, but what guided your intuition / heuristics? Penny for your thoughts? :)
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The other solvents will all react with peroxide to produce nasty explosive compounds, and if you are doing this on your usual multi-ton scale this is a real safety issue.
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While appreciate disco's prep scale experience, I don't necessarily agree with his advice on this question. I'd argue it is all about rates. The commercial preparation of acetone and phenol is from a peroxide intermediate. I'm going to guess this does not explode because of the quantities and decomposition rates.
The poster appears to be asking about a literature reaction for a Bayer-Villiger reaction. If so, why not repeat the reaction. Does it work? As I recall, a Bayer-Villiger reaction will be less apt to occur with acetone as the migrating ability of a methyl group is low. Peroxides decompose at faster rates as the temperature is increased. Running the reaction at reflux is probably going to result in some decomposition of any peroxides. If the hydrogen peroxide is added slowly, the amount of peroxide present can be kept low, below an explosive level. (Check a bottle of toluene for peroxides, it will likely be positive, yet I never worried about it exploding.)
As I recall, I think some terrorists also didn't realize that the acetone peroxide is thermally unstable and decomposes. The result is a dud, oops, not much or no explosion. Even terrorists are subject to the rules of chemistry.
Let us know what happens (or will we read it in C&E News?).
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The other solvents will all react with peroxide to produce nasty explosive compounds, and if you are doing this on your usual multi-ton scale this is a real safety issue.
Found a very interesting Rhone Poulenc 1989 patent about this:
https://docs.google.com/viewer?url=patentimages.storage.googleapis.com/pdfs/US5003109.pdf
Summary: The risk does exist of forming the explosive compounds but not during the reaction per se but more during the subsequent distillation. It specifically lists hydroxylation of an aromatic ring using H2O2 as one example where risk exists yet considerable commercial interest in using the route.
Further it explores conditions where the nasties can be safely gotten rid of. In brief: Add a Copper salt, keep pH above 5 and temperature above 55 C for at least an hour.
I'll have to explore more.
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Let us know what happens (or will we read it in C&E News?).
Well, I sure hope not. :)
Anyways another tidbit I got from an Eni patent:
"Acetone with hydrogen peroxide forms a compound (CH3)2C(OH)(OOH), which is inert in solution, but in the solid state is explosive and can therefore create considerable safety problems during recovery of the product."
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Don't forget about the O2 generation at higher pH.
Excess peroxide you can test for.
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"Acetone with hydrogen peroxide forms a compound (CH3)2C(OH)(OOH), which is inert in solution, but in the solid state is explosive and can therefore create considerable safety problems during recovery of the product."
The explosivity does not surprise me. I'd say this is a general rule, any concentrated peroxide is a potential explosive.
You might wish to look at the commercial production of phenol, http://en.m.wikipedia.org/wiki/Hock_rearrangement
The Wikipedia route does not show a capture of hydrogen peroxide, but I'd be surprised that it should not happen. None the less, I'd think acetone may simply be a hydrogen peroxide carrier. If acetone sequestered all of the hydrogen peroxide, the Bayer-Villiger reaction of an acetophenone would fail. Since it does not and the patent citation using hydrogen peroxide virtually shows acetone does not sequester all of the hydrogen peroxide, I suggest this should not be a worry during the reaction. Isolating and concentrating residual peroxides, of any source, should be a concern. They need to be destroyed or removed. The Bayer-Villiger reaction actually consumes peroxide. I might anticipate that in order to improve the rates, excess amounts of peroxide are used and may be present after the reaction is complete and unless removed, contained in a more concentrated form in the product.
I too had a peroxide education "experience" as part of an ozonization reaction. They can be dangerous, even though not identified as the adduct to acetone has been.
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I seem to recall that this mix was what triggered the TSA prohibition on liquids greater than 3 oz on airplanes, so probably pretty powerful explosive !!
I confirm. The resulting peroxide is a high explosive, very sensitive above all. Though, the reaction conditions may differ (hopefully)
http://en.wikipedia.org/wiki/Acetone_peroxide
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I seem to recall that this mix was what triggered the TSA prohibition on liquids greater than 3 oz on airplanes, so probably pretty powerful explosive !!
I confirm. The resulting peroxide is a high explosive, very sensitive above all.
The solid? Or in solution too?
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I would think it's the solid. But at the liquid/gas interface you may get some deposition of the solid which could cause you some trouble, especially when stirring. This could cause some of the solid to contact each other and cause a minor friction induced decomposition.
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I would think it's the solid. But at the liquid/gas interface you may get some deposition of the solid which could cause you some trouble, especially when stirring. This could cause some of the solid to contact each other and cause a minor friction induced decomposition.
Very good point. Very practical. This is exactly the sort of local phenomenon that causes process disasters. On average a process may seem safe but there might be local fluctuations that create dangerous conditions.
The overall summary I have in mind for now is somewhat like this:
There's no doubt there are severe hazards in the process
OTOH the commercial attractiveness for the route is also very high. The yields n selectivity are high. RM and solvents are relatively cheap. Single processing step and not too hard separations.
Competing routes seem more than marginally more difficult & expensive. More effluent problems.
The hazards do not seem insurmountable if tackled carefully. i.e. it does not seem a stupid, unwarrented or unmitigable risk
Other processes seem to have generated and lived with similar peroxide risks. So lessons may be learnt from those.
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Carrying out an in depth risk analysis to identify hazards and methods for dealing with them will be required. This is not an impossible task. I'm sure that it can be done safely.
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Carrying out an in depth risk analysis to identify hazards and methods for dealing with them will be required. This is not an impossible task. I'm sure that it can be done safely.
Indeed. I agree.
In any case, for now it is only lab experiments with H2O2 doses not exceeding 10 ml or so.
In case the results are promising I'll start the formal hazard analysis process before scaling up.
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London bombings were carried out with acetone peroxide, it was discussed at CF in the past. I believe it is interesting from a thermodynamical POV as the reaction is mostly entropy driven.
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London bombings were carried out with acetone peroxide, it was discussed at CF in the past. I believe it is interesting from a thermodynamical POV as the reaction is mostly entropy driven.
Here's a great paper on the entropic explosion part:
http://tx.technion.ac.il/~keinanj/pub/122.pdf
For oxidation to happen each molecule of TATP would need 10.5 molecules of O2. That's saying 1 gm of the compound needing ~8 Litres of air at STP. (if I did my math right!) That's like saying a volume of TATP would need 8000 equivalent volumes of air at STP to burn completely. Maybe this access is the hard part. I'm speculating that the combustion literally chokes itself.
Decomposition to acetone is enough to cause the entropic explosion OTOH. 3 gas molecules from one TATP.
Caution: Above calculations are my antics. Not in the article. I could be spewing nonsense.
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Thanks for the link.
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TATP fully detonates without air. It's a high explosive (5300m/s). Only the complete combustion would need additional oxygen, what does not happen in the detonation (but the initial TNT-like detonation then transforms the reactor's contents in an air-breathing bomb, and may detonate the concentrated hydrogen peroxide as well).
The Wiki article seems voluntarily botched. The London bombings were carried using TATP.
In your risk analysis, will you detonate some TATP too see what happens then? To get an intuitive idea of how sensitive and powerful it is. Better try a tenth of a gram before having tons.
From the linked Pdf, second paragraph: "TATP is one of the most sensitive explosives known" and "with power close to that of TNT". This does of course not rely on additional air.
Beware the linked Pdf has only estimated the heat of formation by software. More serious sources measured +91kJ/mol and +151kJ/mol - and this does not include the partial combustion, for instance 6* 110kJ/mol for the CO, unless you do believe that a detonation produces ozone besides hydrocarbons.
Primary Explosives, By Robert Matyáš, Jiří Pachman (available from Google Book)
and
http://onlinelibrary.wiley.com/doi/10.1002/prep.201100100/abstract
Maybe you could drag Anders Hoveland in this conversation, if he's still reachable? He has practical experience with explosives, at least in lab amounts.