nightshade
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peracids
hey when making a ketone using using peracid, what acids can be combined with h2o2 to make a usable peracid.
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Klute
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That depends how you "make a ketone". Are you talking about epoxidation of an alkene? Bayer-Villiger oxidation?
Alot of acids form peracids readibly with H2O2, but the most common are formic, acetic, and sulfuric. A quick search would have revealed that. Other
peracids such as m-chloroperbenzoic acid, perphosphoric acid, perphtalic acid, peroleic needs more involved conditions.
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Nicodem
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The question is too unspecific for a useful reply. I'm moving this to Beginnings in case the original poster decides to explain what he is asking. I
know of no reactions using peracids that would yield a ketone except for the oxidation of secondary alcohols for which peracids are not really
appropriate reagents (since they react with the resulting ketone as well, often much more rapidly).
The Baeyer-Villiger oxidation yields esters (or sometimes phenols with aromatic ketones, if the resulting esters are unstable toward hydrolysis in
aqueous media), while the epoxidation of alkenes yields epoxides (or sometimes glycols in aqueous media if the epoxides are unstable toward hydrolysis).
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Klute
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If of course ketones can't be directly obtained through those reactions, but BV reaction of an a,b-unsaturated ketone yield a enol ester which gives a
ketone upon hydrolysis, and the gylocol/epoxide obtained with a alkene can rearrange to ketone with acidic reflux as you mentionned.
I guess the poster just skipped the steps and only considered the pathway to ketones.
Indeed, the question is too unspecific and in any case a little searching would have sufficed.
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nightshade
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the epoxidation of alkenes. now can one use boric acid to make peracid?
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Nicodem
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Depends on the nucleophilicity of the alkene, its substitution, conjugation, etc. Your question is way too unspecific for any useful answer.
About perborates... Enones can be easily epoxidized with sodium perborate, but they and other such conjugated electrophilic alkenes can usually be
epoxidized even with plain hydrogen peroxide in basic media. But the mechanism of epoxidation of enones is completely different from the epoxidation
of nucleophilic alkenes. For the epoxidation of some nucleophilic alkenes, sodium perborate in acetic acid can be used (see: Tetrahedron, 51,
(1995) 6145-6166).
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Klute
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Here a document related to the use of borax-H2O2 to form insitu perborates used in Bayer-Villiger oxydations. In this case, oxidation of unsaturated
ketones give epoxidesas Nicodem wrote. I'm pretty sure i've seen similar articles for alkene epoxidation with either borax/h2o2 or direct perborate.
My guess is yes, it should work. Try finding some revelant literature.
[Edited on 4-4-2008 by Klute]
Attachment: PerborateInSitu.pdf (325kB)
This file has been downloaded 1242 times
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angelhair
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performic preparation question
Usually I mix the two in a beaker, H2O2 about 4deg C and Formic about -7 Deg C, leave on the bench for 1 hr then in the freezer till about 0 Deg.
This timeI want to prepare as aboue, then stick it in the freezer is a sealed PE bottle. Depending on the quantity, It may be in the freezer for up to
2 hours.
Will it develope any pressure in the bottle?
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Nicodem
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In two hours in a freezer not much of the performic acid would decompose, so not much of pressure would develop (unless your formic acid contains
traces of metallic ions or other contaminants that catalyze the decomposition of hydrogen peroxide).
But why not just screwing the stopper less tightly if you are worried of the bottle blowing up?
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angelhair
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I was worried about my sinuses more than any thing else. Usually I just cover with plastic wrap, then when I go back to the freezer I forget that I'm
going to smell the stuff and bang, blocked nose for another 2 weeks.
I did try puting it in a tightly sealed bottle and in the freezer for 90 min and it was OK. No pressure at all.
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Fyndium
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A bayer-villiger synthesis asks for perborate. Can it be substituted with hydrogen peroxide in a molar eq? There was discussion that percarbonate is
unsuitable for the reaction.
Perborate could be made from borax, NaOH and H2O2, but if this borate step is unnecessary, it would save a trouble.
[Edited on 11-10-2020 by Fyndium]
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clearly_not_atara
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Quote: Originally posted by Fyndium  | | A bayer-villiger synthesis asks for perborate. Can it be substituted with hydrogen peroxide in a molar eq? There was discussion that percarbonate is
unsuitable for the reaction. |
I would not recommend it. However it may be possible to produce perborate in situ by rxn of H2O2 and Na3B3O6. The latter known as sodium metaborate is
preferred for making perborates.
The active reagent in perborate oxidations varies but is often interpreted as being the hydroperoxytrihydroxyboronate(III) species (OH)3BOOH- which is
not present in solutions that lack boron. This species is particularly suited to transfer an equivalent of OOH- to a carbonyl group since the freed
B(OH)3 may then complex with the carbonyl oxygen.
It might also be possible to produce perborate by rxn of metaboric acid H3B3O6 with sodium percarbonate.
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Fyndium
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It seems that perborate is actually easy to produce if H2O2 is available. It is basically done by dissolving borax, adding sodium hydroxide and then
H2O2 and collecting the crashed out perborate.
There are some sources that cite Baeyer-Villiger done with H2O2, but it seems that the aqueousness is an issue on it's own, since the perborate is
dissolved in GAA medium in other source, which indicates so.
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