[naitsabes]

Hey Guys,

I have a question regarding a reaction mechanism. I did an N-acylation (amine to N-propanoyl...) with propionic acid and to my own surprise it worked (quite good).

But to be honest, I do not really know why. Normally you take an anhydrid or an acid chloride for such a reaction. Why does it work so well with simple propionic acid, when it would never work with acetic acid (at least I thought so... but definitely it would not work well I think).

I can think of two explanations, but both are not convincing to me:

-) Propionic acid has a higher boiling point than acetic acid. But than one would just have to cook it longer with acetic acid and I don't think this would work (my reaction took 2 hours at reflux btw).

-) Propionic acid is a weaker acid, therefore there are more molecules which are not deprotonated and in these the carboxylic carbon is much more susceptible for nucleophlic attack of the nitrogen.
Sounds nice (Or do I mistake something?), but I don't think that 4,87 vs 4,75 makes such a difference?

Does anyone know the solution? Or just an idea?

Thank you!

[Babcock_Hall]

This is just a guess, but perhaps the thermodynamics of this reaction are as important as the kinetics.