September 17, 2021, 08:46:25 PM
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Topic: Stability of specific nitrones under heat? Melting points as reference in post  (Read 59 times)

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Offline donaxad704

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I want to recrystallise a nitrone of a synthesis I did. The compound is Disufenton Sodium, a variant of the alpha-Phenyl-N-tert-Butyl Nitrone which has two sulfonic groups in addition. The synthesis itself happened under nitrogen atmosphere in refluxing methanol for around 24 hours. I already checked the synthesis with NMR and indeed obtained the desired nitrone. The only difficulty left is doing the purification. For the recrystallisation I want to use ethanol under reflux (i.e. 78 degrees celsius). If necessary also under nitrogen atmosphere. My worry (or rather the one of a colleague) is that the nitrone might decompose under these conditions (i.e. the higher temperatures). Hence I want to ask whether this is the case (i.e. whether 78 degrees will cause degradation) and if not what temperatures might be problematic.
I have found a great source that contains at the end example synthesises of many aromatic nitrones derived from a-Phenyl-N-tert-Butyl Nitrone but with additional functional groups. I linked the source path the end of this post. The important things one can find is that in most cases benzene is used as solvent for the synthesis and the synthesis happens under "gentle relux" for mostly more than 16 hours. I assume that this implies temperatures of around 80 degrees can be assumed for the time of the synthesis. The melting points of many of these compounds are much higher. Just to name a few:

  • alpha-N-Diphenyl Nitrone: 112°C
  • alpha-Phenyl-N-tert-butyl Nitrone : 74°C
  • alpha-(4-Hydroxyphenyl)-N-tert-butyl Nitrone (PBN-OH): 228°C
  • alpha-(4-Nitrophenyl)-N-tert-butvl Nitrone (PBN-NO2): 139°C

My assumption is that the examples mentioned proof that the common denominator ( the phenyl ring+the nitrone part and the N-tert-butyl part) is stable up to high temperatures of well above 100 degrees celsius as otherwise the nitrones might degrade and could not melt at say 228°C. However, this assumption is based on the belief, that the additional groups on the phenyl do not influence/increase the stability of the 'nitrone part' of the molecule. In any case I am mostly interested whether the Disufenton Sodium will degrade if one tries to dissolve it in neat ethanol at 78 degrees with or without nitrogen atmosphere. If so, I would probably have to use/try other solvents for the recrystallisation.

I am very thankful for any feedback on this regard!
Thank you in advance!

P.S. the source for the above mentioned samples and many more is:
« Last Edit: September 10, 2021, 11:42:13 AM by donaxad704 »

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