AAMC Organic Chem Mechanism Question?

[stester77s]

I attached an image of the mechaism in question. My question, is how does the middle oxygen get protonated while the other oxygen has a negative charge? Shouldn't the oxygen with the negative charge get protonated before the neutral oxygen?


What is the name of this synthesis (so I can look up alternative mechanisms)?

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[tdod]

my best answer is that the alkoxide oxygen probably does pick up a proton first. however, there is no way to break up the compound, so eventually that proton gets lost. in contrast, when the central oxygen picks up a proton, the compound can collapse and will not reform.

 

[syoung]

Actually that mechanism looks weird on a couple of levels. What's the solvent? That would determine how the mechanism proceeds.

 

[SuperSneaky24]

So my guess is that what you said also occurs (that the negative oxygen is protonated instead). What you'll get is both forms, kind of like a keto-enol tautomerization but not exactly the same. It is the form in the image that is reactive and will cause the forward reaction to occur.

http://chemwiki.ucdavis.edu/Organic...d_Anhydrides_React_with_Amines_to_Form_Amides
Found the reaction online, except that hydride shift never occurs, so it's probably not that critical of a step

 

[DrknoSDN]

So my guess is that what you said also occurs (that the negative oxygen is protonated instead). What you'll get is both forms, kind of like a keto-enol tautomerization but not exactly the same. It is the form in the image that is reactive and will cause the forward reaction to occur.

http://chemwiki.ucdavis.edu/Organic...d_Anhydrides_React_with_Amines_to_Form_Amides
Found the reaction online, except that hydride shift never occurs, so it's probably not that critical of a step

Nice, I was about to repost the same link as you. It does show a better mechanism.

To find lots of mechanism pictures just search google images and type all the functional groups... I.E. "Anhydride Amine Amide", pops right up.