[DavidF]

In the above reaction, what is the action of Triethylamine ?
I believe it acts as a base protonating the amine, not sure though.

i'd be happy for more ideas

thanks,
David

[StarvinMarvin]

How would a base protonate anything? It would rather attack the anhydride and thus facilitate the amine addition to the carbonyl carbon atom.

[DavidF]

sorry, i meant DEPROTONATING the amine (typo)

as for your response, what the Et3N will attack exactly ?

[James Newby]

Triethylamine just removes acidic protons during the reaction.  The primary amine opens up the anhydride and the nitrogen is bonded to 4 things with a formal positive charge.  Triethylamine is more basic than the primary amine so deprotonates it.

The second part is the same and the triethylamine again removes the acidic hydrogen giving the neutral imide

[Arctic-Nation]

In this case, the formal role of triethylamine is to facilitate the exchange of protons between reactants, products and intermediates. Don't forget that water is the second reaction product.

Depending on the exact reaction mechanism, triethylamine also might open up the anhydride as the first step, but in this case the primary amine probably is more reactive.

[orgopete]

Without looking this up, this looks like the Org Syn prep of phthalimides from amino acids. If not that reaction, then it won't result in the product indicated.

If you were to mix the two reagents together without triethylamine. The reaction would slow down halfway through the reaction with the newly formed carboxylic acid protonating the amine. You could add triethylamine to release the amine and allow the reaction to go to completion. In this case, the product will be the amide-acid as its triethylammonium salt. However, with phthalic anhydride, that isn't necessary. The reaction will go to completion without any triethylamine. Amines can be protected from acylation by forming a salt with HCl, but even this does not completely protect the amines.

If I am remembering correctly, in the Org Syn prep, a catalytic amount of triethylamine is used with phthalic anhydride and an amino acid heated in toluene with a water trap. In that case, I think triethylamine is used to solubilize the amino acid and increase the reaction rate.

I am at a disadvantage in trying to guess how you are doing the reaction. If I were doing this reaction, I would skip the TEA.

[spirochete]

Everyone is correct so far, but no one has pointed out why your original idea is so unlikely. 

Triethylamine deprotonating the primary amine would be a fairly disfavored acid base reaction.   R₃NH⁺ has a pka of about 9, but RNH₂ has a pka of about 38.  So this is an acid base reaction that produces a much stronger acid, meaning it's going to happen very little at equilibrium.  This would lead me to look for other ideas about the role of the triethylamine. 

[orgopete]

Everyone is correct so far, but no one has pointed out why your original idea is so unlikely. 

Triethylamine deprotonating the primary amine would be a fairly disfavored acid base reaction.   R₃NH⁺ has a pka of about 9, but RNH₂ has a pka of about 38.  So this is an acid base reaction that produces a much stronger acid, meaning it's going to happen very little at equilibrium.  This would lead me to look for other ideas about the role of the triethylamine. 

I've done this reaction with phthalic anhydride. With a basic amine, triethylamine is not needed for the reaction to occur.

Triethylamine is used in the Org Syn prep with phenylalanine, http://www.orgsyn.org/orgsyn/pdfs/CV5P0973.pdf
It is not used with ethanolamine, http://www.orgsyn.org/orgsyn/pdfs/CV4P0106.pdf

With an amino acid, the reaction is slower. Amino acids are insoluble in toluene. I think triethylamine is added for solubility. I am still guessing that this is a vestigial use from the Org Syn prep. I have witnessed people borrowing procedures from other experiments and if it works, they don't alter it.

Triethylamine might help to suppress the formation of some by-product. If we knew what the by-products were or even the stoichiometry of the reaction, we could guess how it might serve a useful role. However, I really don't see why it should be added. If you wished to acetylate benzylamine with acetic anhydride, I think this will occur very readily without triethylamine. Just my opinion.