[_Espard_]

Pretty straightforward question, but I can't seem to find much of a direct answer.

Are N-oxides (i.e. pyridine-N-oxide, N-methylmorpholine-N-oxide) stable in aqueous alkaline solution?

[Sir_Goat]

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.

[Dan]

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

[orgopete]

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?