[foxfourfive]

Hi all,

I'm melting a sample of an amino ketone in a vacuum oven and keep running into the same problem.

Basically the recorded melting point of the compound is 217-218°C, and I'm heating it in a partial vacuum (so it doesn't evaporate) and nitrogen filled so it doesn't oxidize, but no matter what I do it ends up brown, sticky and smelling burnt. The result I'm after is a melt recrystalisation with no decomposition but I'm unsure of what is going wrong. I understand that the vacuum only lowers the boiling point, not the melting point, but I feel like by the time it melts it has already decomposed.

Can anyone tell me what I'm missing? I'm due to have this completed late today and starting to become extremely frustrated.

[kriggy]

Did you analyze your sample after melting? It just might look like decomposed but it can be fine

[Enthalpy]

Do the amine and ketone functions react to make a cross-linked polymer?
Dissolve instead of melting?

I don't understand the usefulness of vacuum. It won't change the melting point, but helps evaporation. To avoid evaporation, a higher pressure would help. And in fact, nitrogen pressure only helps against boiling; against quiet evaporation, only the partial pressure of your compound helps.