Electra
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Is auto-condensation a risk in preparing nitroalkane enolates?
Specifically with longer chain nitroalkanes, 1 (and 2) nitropropane, 1-nitrobutane, 2-nitrobutane, etc.
I found that nitroethane reacts to form nitronate salts, but what exactly is formed is not specified. Condensation products? I found another link
elsewhere that specified the synthesis of Eph that involved preparing two solutions, one of which was Nitroethane + NaOH, and then combining the
solutions, implying the auto condensation does not occur? Why is this?
http://msdssearch.dow.com/PublishedLiteratureDOWCOM/dh_0035/...
I've never heard of this being an issue with mild deprotonating agents such as amines, but is there a risk of irreversible self-condensation when
using NaOH to prepare these enolates? I could imagine the two deprotonated hydrogen coming up and reacting with the OH- anion to form water, leaving
Na+ in the solution with the newly condensed dinitro compound.... but I am not sure if the properties of Nitroalkanes can allow for this due to the
strong electron withdrawing effects. I have also read of people preparing such nitronate salts but haven't found much on if any special procedure is
to be used.
I have found instances of NaOH being used in Nitroaldol reactions in very low ratios (0.025m) with a PTC. I always assumed NaOH wasn't used because in
condensations with aldehydes the NaOH is returned to the solution which leaves it able to induce an over condensation of the product. I am more
interested in preparing the nitronate salt for temporary storage and usage in other reactions that won't return the NaOH back to solution.
If the nitronate salt cannot be isolated, then keeping it in the solution is an option, though I need to be aware of whether or not condensation of
the enolate with a free nitroalkane is possible, or how it might be avoided.
[Edited on 16-4-2014 by Electra]
[Edited on 16-4-2014 by Electra]
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Nicodem
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Quote: Originally posted by Electra  | | If the nitronate salt cannot be isolated, then keeping it in the solution is an option, though I need to be aware of whether or not condensation of
the enolate with a free nitroalkane is possible, or how it might be avoided. |
What enolate? The deprotonation of the nitroalkanes gives the corresponding nitronate anions. None of the nitroalkanes that you listed contains any
carbonyl groups, hence they cannot form any enolates, so no self-condensation is possible.
…there is a human touch of the cultist “believer” in every theorist that he must struggle against as being
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scientific temper, not in the scientific defense of the theory. - Weston La Barre (Ghost Dance, 1972)
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Electra
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Sorry for mixing up the terminology. I for some reason was considering any deprotonated active hydrogen compound an enolate. I suppose nitronate is
etymologically more correct.
I was wondering because the nitronate anion can effectively as a nucleophile, and the nitroalkane by itself can act as an electrophile.
I did some further reading and it seems the condensation is possible, but it seems to not happen very easily, and seems to require much heating. It
would seem that most nucleophilic addition/substitution reactions that use deprotonated nitroalkanes happen exponentially faster than any potential
self-condensation.
Nitromethane on the other hand seems to be an exception, reacting with itself very quickly, as some users here have reported.
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