Doc B
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Extremely strong bases for enolization
Is there any suggestions for a convenient extremely strong base, obtainable for the hobbiest, that is able to tautomerise acetone to the enol?
http://en.wikipedia.org/wiki/Keto-enol_tautomerization
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sargent1015
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Is NaOH not an option?
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UnintentionalChaos
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Not if you want quantitative conversion. Probably sodium amide is a solid choice.
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Doc B
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SGT: no NaOH's conjugation pKa is not high enough.
UC: the sodium aide is defiantly an option, however it's acquisition &/or synthesis (al la Vogel) is currenty precluding it.
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kristofvagyok
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Sodium-isopropoxide or sodium-tertbutoxide will do it.
NaOH is a weak base fot this.
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DJF90
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Sodium hydride is a good choice, as is sodamide. What do you want quantitative enolate formation for? What reaction are you doing? Have you tried
using an enolate equivalent, e.g. enamine?
Hydroxide is actually a very strong base its just the fact most reactions are performed using it in aqueous solution. In methanol solution, I've used
KOH to deprotonate an acetylene (pKa of phenylacetylene is ~28) prior to reaction of the anion. Phase transfer catalysis in say toluene has also been
used to deprotonate very non-acidic protons, those that would typically be taken using sodamide or LDA or KHMDS. I think the problem with this
application is the fact that quantitative conversion needs to occur rapidly, to avoid self condensation. I don't know how such systems stand up on
this basis.
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AndersHoveland
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I have a feeling that sodium amide would cause a different reaction, particularly in the absence of any other reactant.
"The cleavage of ketones by sodium amide was discovered in 1906 by Semmler"
see the Haller-Bauer reaction
R-CO-R' --> R-CO-NH2 and H-R'
not sure if this only applies to non-enolisable ketones
[Edited on 6-11-2012 by AndersHoveland]
I'm not saying let's go kill all the stupid people...I'm just saying lets remove all the warning labels and let the problem sort itself out.
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zed
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Ummm. Enolize Acetone....Might be difficult to do by ordinary methods. A relatively useful method for forming the enol of Acetone, is reacting
acetone with Ketene.
The resulting product is Isopropenyl Acetate. The Acetate Ester of Acetone Enol.
The product is commercially available at less than $100.00 U.S./Liter.
Ketene itself, isn't too hard to generate, but its use is fairly dangerous. Given the chance, it will rip though your lungs like a raging
Roto-Rooter.
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Doc B
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The MeOH sounds the most convenient. Ketene is another good option and easy to obtain for the hobbyist. However being that my eyes still feel like
sand paper from my last experiment synthesising formic acid and alkyl alcohol, I'm not sure I'm an enthusiastic enough hobbyist to risk a good waft of
ketene at the moment.
The enol is theorised to be used in a halo condensation. Most of the super bases mentioned will work but the acquisition is out of my range at
present. I'll give the MeOH a go first and report back.
Cheers
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DJF90
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A halo condensation? You mean halogenation? Depending on your substrate, you may suffer from regioselectivity issues. If the molecule is symmetrical
(e.g. acetone) then this is of little concern. Monohalides are typically formed under acidic conditions, if that helps.
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Doc B
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Quote: Originally posted by DJF90  | | A halo condensation? You mean halogenation? Depending on your substrate, you may suffer from regioselectivity issues. If the molecule is symmetrical
(e.g. acetone) then this is of little concern. Monohalides are typically formed under acidic conditions, if that helps. |
The enol displaces the halogen, I'm not exactly sure of the reactions name. I guess it's an Adol condensation?
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SM2
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| Quote: Originally posted by zed | Ummm. Enolize Acetone....Might be difficult to do by ordinary methods. A relatively useful method for forming the enol of Acetone, is reacting
acetone with Ketene.
The resulting product is Isopropenyl Acetate. The Acetate Ester of Acetone Enol.
The product is commercially available at less than $100.00 U.S./Liter.
Ketene itself, isn't too hard to generate, but its use is fairly dangerous. Given the chance, it will rip though your lungs like a raging
Roto-Rooter. |
if you filled a flower jar w/ acetone, and had a nice coated Pt catylist floating and fixed above, could you just heat the catylist, and then, it
would be exothermic, with the evaporation sendingg a stream of acetone over the glowing Pt?
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ScienceSquirrel
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| Quote: Originally posted by Fennel Ass Ih Tone | | Quote: Originally posted by zed | Ummm. Enolize Acetone....Might be difficult to do by ordinary methods. A relatively useful method for forming the enol of Acetone, is reacting
acetone with Ketene.
The resulting product is Isopropenyl Acetate. The Acetate Ester of Acetone Enol.
The product is commercially available at less than $100.00 U.S./Liter.
Ketene itself, isn't too hard to generate, but its use is fairly dangerous. Given the chance, it will rip though your lungs like a raging
Roto-Rooter. |
if you filled a flower jar w/ acetone, and had a nice coated Pt catylist floating and fixed above, could you just heat the catylist, and then, it
would be exothermic, with the evaporation sendingg a stream of acetone over the glowing Pt? |
That sounds like an excellent way to get a good solvent fire going.
Acetone is quite volatile and flammable.
This is how you should go about it.
http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=cv1...
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Salmo
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I think you need a really strong base to move the equilibrium between the two tautomers, LDA maybe? i think sodium amide would be a nucleophile other
than a base.
sodium/potassium tertbutoxide would work too, something that is a strong base but too big to be a good nucleophile too..
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DJF90
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Its alpha-halogenation of a ketone/aldehyde. Like I said, if you want mono-halogenation, a good method is to use e.g. bromine in acetic acid. Under
basic conditions, halogenation tends to be exhaustive e.g. methyl ketones undergo the haloform reaction. Complete formation of the enolate and
reaction with an electrophilic halogen source (e.g. N-Halosuccinimide) will also work. Again, I'll mention the regioselectivity issue you may
or may not have; you'll get more help if you can be more transparent regards your substrate.
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chemrox
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Na shot in xylene - it's cheap and convenient
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DJF90
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You sure you wouldn't get competing pinacol coupling, Chemrox?
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TheChemINC
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what about something like sodium methoxide?
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