[prozen]

A reaction I've tried several times in the past is the hydrogenation of nitroimidazole derivative shown below. The amino product is extremely unstable and rapidly decomposes.

This instability is noted in may pieces of literature and the explanation tends to only go far as saying 'ring fission' occurs.

Question: What is the mechanism of this ring fission? To be clear, I am not interested in getting this reaction to work.... It is no longer a target of mine.

Perhaps the entire mechanism is not determinable, but I presume the amine of one molecule attacks another molecule's imidazole ring? Where would this be? How is fission occuring?

Possibly something to do with the apparently favoured tautomerism between these two forms:

[rolnor]

I think you could trapp the amine if you have some Boc-anhydride present in the hydrogenation step.

[prozen]

I think you could trapp the amine if you have some Boc-anhydride present in the hydrogenation step.

This is true, but I'm currently more interested in why this amino product is so unstable.

[Enthalpy]

Would it be conceivable that the hydrogenation doesn't stop at the aromatic amine but proceeds to the saturated geminal polyamine, which is unstable?
(Apologies in advance if I put nonsense)

[rolnor]

If you get the Boc-amine you could deprotect with acid and se if the amine is stable under acidic conditions, and if so you can make the free base and se if that breaks down.