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Author: Subject: How to cleave a ketone
detritus
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How to cleave a ketone

Thanks in advance for tolerating my newbie questions here..

I wanted to know a good method to oxidatively cleave a ketone like acetone or MEK.

I was sure permanganate would do it, but my classmate assured me that acetone at least would not be further oxidized by MNO4.
Klute
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How do you want to cleave it?
A haloform would give the acid with one carbon less. A bayer villiger on MEK (no reaction with acetone) would yield acetic acid and ethanol (pôssibly oxidized to more acetic acid depending on the conditions) IIRC.

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detritus
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baeyer-villiger seems like it would work just fine, thanks. any tips on an otc way to do it? trifluoroacetic, peracetic, and CPBA seem like they are more expensive than is worth it.

http://www.organic-chemistry.org/namedreactions/baeyer-villi...
Klute
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Peraectic, performic, or even more OTC persulfuric acid!

H2SO5 is generated from either peroxodisulfate salts (S2O8 2-) and H2SO4, or oxone/H2SO4. I have a neat patent on forming H2SO5 solution is good yieldwith ammonium/potassium/sodium peroxodisulfate and conc. H2SO4, I'll dig it for you later one. Works great for BV oxydations.

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Sauron
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You can pyrolize acetone to ketene on a lab scale with a "ketene lamp" or on any scale with a tube furnace. Ketene is very reactive, corrosive and toxic, carcinogenic, and these properties are not lessened when it is 700 C or so. This is not a procedure for a newbie.

Other than that you might get acetone to fall apart to carbon oxides and soot (soot being a byproduct in ketene process) but I do not know of any way to get anything more useful out of it.

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Klute
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See US 4,049,786 for preparation of persulfuric acid from peroxodisulfates and conc. H2SO4.

The attached article claims 100% yield sof ethanol and acetic acid from MEK with K2S2O8/H2SO4. This will also show you the reaction conditions used.

Attachment: JOC_35_3080-3082_1970.pdf (428kB)

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detritus
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thanks to both of you. no ketene for me, though - that stuff seems pretty awful.

acidified persulfate looks cheapest if i gather that correctly from your post, klute. i was just looking for other routes to basic lab stock, so i did not want to use anything fancy. post that patent info whenever you get a chance, it seems interesting.

any tips on the BV? notes from a rxn you did?

whoops, took too long to post, you already replied! i will look at the patent for their conditions in the MEK rxn. thanks!!

[Edited on 22-5-2008 by detritus]
DerAlte
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@Detritus

My experience has been that permanganate will oxidize acetone, provided water is present. KMnO4 is soluble in dry acetone but will react (fairly slowly) with a solution, assumedly to acetate and perhaps formate plus MnO2. Don't know about MEK but suspect it will also do same due to enol formation. What product are you trying to obtain?

Der Alte
detritus
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acetate and formate, actually. i was just musing on the topic, trying to increase my knowledge of chemistry.
Klute
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Well, for acetate, you would better be off oxidizing ethanol, no?
And you could obtained the formate by doing a haloform reaction on ethanol, giving some usefull haloform too. Just do not acidify the formate with conc. H2SO4 if trying to get formic acid you will generate CO gas.

Using ethanol would surely be wiser economically-speaking. MEK is pretty expensive compared to ethanol. You could be able to make some propionic acid from it with a haloform, but I think the process is much less efficent than with acetone.

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MagicJigPipe
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In my part of the world MEK is much cheaper than EtOH. Especially when "bulk" rates are compared.

For me anhydrous EtOH is $6.35 a gallon (95% not too much cheaper. And without denaturants it is an ungodly$15.50/L) and MEK is $4.25 a gallon. Acetone is even cheaper at$3.35/gallon.

Hardware store rates are different but still in the same order from least expensive to most expensive: Acetone, MEK, Denatured EtOH (w/ MeOH).

Also, Klute, what is the "typical" method for obtaining formic acid from formates? Phosphoric acid?

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detritus
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and don't forget the cool factor. i don't really need any of the reaction products, but to oxidize and rearrange good old acetone or MEK into an ether is just.. well.. cool!

speaking of peracids and cool things: anyone ever see this patent?

US5462692 - Stable solid acetylperoxyborate compounds

you have to vacuum dehydrate your perborate (60C, 25mm, 1h - from another patent) to get the monohydrate, but then just add GAA and you got stable, solid peracetyl borate.

what's it good for you say? just dump this magic powder into water for instant peracetic acid of your desired concentration. pretty neat!
not_important
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 Quote: Originally posted by MagicJigPipe ... Also, Klute, what is the "typical" method for obtaining formic acid from formates? Phosphoric acid?

You can use sulfuric, but only as a cold diluted acid; then distill to get the 75 percent acid (excess of formate so no free H2SO4). With calcium formate, using concentrated HCl should give you two layers, one of fairly concentrated formic acid and the other of strong CaCl2 solution; separate and treat the formic acid with additional formate to clean up any excess HCl.

Molinari and Pope's Treatise on General and Industrial Organic Chemistry (out of copyright) discusses using sulfuric acid, as do other old chemistry books.

Odder methods include heating stearic acid with sodium format, while stearic acid is weaker than formic it is much less volatile so the formic acid can be distilled out of the (messy) mixture. Oxalic acid can be used instead, but some of it may come over with the formic. Treating lead format with H2S is another.
Klute
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Detritus, that patent on the use of perborate to form peracetic acid is said to work very well. It tried it for a bayer villiger some years ago, and worked very nice, although you do have a thick slurry to stir and latter filter/extract. The reaction is best conducted near 40-50°C, even up to 60°C.
There is hardly any difference when using the mono-hydrate, the amount of water introduced is still kept minimal, so you can directly use what you have.

Basic perborate/H2O2 is said to work for Dakin type reactions, aswell as epoxidation, and perhaps BV when no other reaction si possible (it will favor epoxidation over BV in the case of a,b-unsaturated ketone though).

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detritus
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the most interesting thing about that patent is that you can create a dry, stable form of peracetic that can be used later. i was thinking they wanted the monohydrate in order to push the balance over to the peracetyl borate (PAB) side rather than the aqueous peracetic side.

it seemed to me that if the mixture has too much water, most of the consitutents will exist as peracetic and degrade by the time you dry them out. but yep, if you just want PAA right then and there, the water content is not a big deal.
Klute
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Yes, but you would better be off storing the perborate . And just generate the peracid (other acids can be used) when you need it

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Jome
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How about reacting it with a sulfite to get an organic acid and a sulfonic acid, or am I missing something? (I obviously am)
Klute
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Reacting what with sulfite? The peracetyl borate? That would just give you sulfate, acetate and borate ions..

reacting acetone or MEK will give you the addition compound of each ketone with bisulfite:

Me-C(O)-R + HSO3- --> Me-C(OH)(SO3-)-R

with R= Me for acetone and R=Et for MEK.

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Jome
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No, the sulfite (SO3-2). I was under the impression the result would be a sulfonate of one of the R-groups, but I cannot find the reference despite 45 frenzied minutes of searching.
Klute
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But how could a sulfite form a sulfonic acid with a ketone? Loosing a proton doesn't chang the sulfite capabilities to that extent. The only recation would be an nucleophilic addition on the carbonyl, forming the adduct. If the pH is too high, the adduct will not form, that's why the reaction is usually written with bisulfite, which predominates at neutral pH.

The only way of forming a sulfonic acid with sulfite would be an electrophilic addition on a carbocation, like in the Bucherer reaction, which is not going to happen here!
How would a sulfite break a CO-C bond? Leaving a O=C(R)- ? Unlikely!

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Ephoton
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I have made a lot of formic in my time and H2S is not a pritty way to go.
I will never and I mean never try it again.
oxalic was the cheapest with glycerol and then use the cold sulfuric to
get a concentrate.

then use boric anhydride to get it near pure.

very expensive though.

I have had very little success with beayer villagers with persulfates
unless they were in acetic acid which kind of kills the whole reason to
use them.

I have found that kodak stop bath is 90% acetic acid and when mixed
with some 98% sulfuric acid and 50% peroxide found at the hydro shop.
or if you can only get 30%, slowly heat it under vacuum to around 70C as
stated some were on this board you will get a nice peracetic mix.

you can buy peracetic premade as a cleaning solvent from many cleaning companys. I can not remeber the name at the moment peroxy or something like that but it might save you a lot of time.
it can be purchased with out id or address in large volumes as well.

I still go for performic my self as I like the smell sick arnt I.

[Edited on 14-6-2008 by Ephoton]

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 Sciencemadness Discussion Board » Fundamentals » Organic Chemistry » How to cleave a ketone Select A Forum Fundamentals   » Chemistry in General   » Organic Chemistry   » Reagents and Apparatus Acquisition   » Beginnings   » Responsible Practices   » Miscellaneous   » The Wiki Special topics   » Technochemistry   » Energetic Materials   » Biochemistry   » Radiochemistry   » Computational Models and Techniques   » Prepublication Non-chemistry   » Forum Matters   » Legal and Societal Issues   » Test Forum