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Mike Jones

Are N-oxides stable in aqueous alkaline solution?

Chang Liu  Follow
Re posters original question. I'd expect the N-oxides to be reasonably stable. If pyridine-N-oxide were dissolved in water and made basic, I wouldn't expect anything to happen. Did something happen?

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Brian O'Sullivan  Follow
I guess another sensible question to ask is what would happen in acidic solutions? My guess would be that the oxygen would be protonated and become a leaving group, leaving you with, for example, just pyridine.

So I guess it depends how alkaline your solution is? The more H+ available the less stable the compounds.

Seems logical to me anyway but I guess this would explain why there there's no obvious straightforward answer: It depends on the pH of your solution.

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Banti Singh (???? ????)  Follow
Quote from:
My guess would be that the oxygen would be protonated and become a leaving group, leaving you with, for example, just pyridine.

No, that would give you Py2+, which won't happen. To get pyridine from pyridinium N-oxide you need nucleophilic abstraction of O - i.e. the Py is the leaving group, not hydroxide/water.

I'd guess that SNAr reactions (for example with hydroxide: pyridine N-oxide :rarrow: 2-pyridone) would be a more likely degradation pathway - but I don't know the answer to the OP's question.

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