[jabi3jabi3]

Hi guys,

so I just performed a lab experiment where aniline is being turned into an amide using glacial acetic acid and acetic anhydrous. After searching everywhere online, it was stated everywhere that only acetic anhydrous is needed for the reaction and that acetic acid is a bi-product. So my question is why did our lab want us to add both (2mL of each) glacial acetic acid and acetic anhydrous to the aniline product? I understand the mechanism of using acetic anhydrous but i dont understand the mechanism or the reason behind using both.

thankyou

[rolnor]

You mean acetic anhydride? Can you draw the reaction?

[jabi3jabi3]

You mean acetic anhydride? Can you draw the reaction?

hi yeah sorry i meant acetic anhydride. And that's the thing I don't know how to draw it because i dont know what the acetic acid is for

[Babcock_Hall]

In some steps a molecule of solvent acts as acid or a base.  That might be the case here.

[rolnor]

Could the acetic acid be partially protonating the anilline to make it less nucleophilic, to make the reaction less vigorous?

[wildfyr]

I agree with rolnor, this reaction should be done under basic conditions. Using acetic acid up front is just plain incorrect in my book. The aniline is a base, and when you protonate it it becomes non-nucleophilic, and non-acetylatable.

[Babcock_Hall]

The pK_a of the conjugate acid of aniline is between 4 and 5.  I doubt that protonation of aniline is complete.  The synthesis is performed in glacial acetic acid, which is empirical evidence that the reaction proceeds.

[rolnor]

I did wright "partially protonated", I think this is the reason to use acetic acid, to slow the reaction down.

[Babcock_Hall]

I would put forth the hypothesis that there is acid catalysis occurring, but I don't have experimental data that bears on the question.

[wildfyr]

Acetic acid as a solvent would see to work against this reaction via Le Chatlier