p-Nitroacetanilide synthesis

[Bioc]

Hi, I was wondering why the nitration of acetanilide requires the use of sulfuric acid AND acetic acid. I understand that the acid medium is used to solubilize the acetanilide, so why is concentrated sulfuric acid alone not enough? On a side note, the sulfonitric solution is prepared in another tube and later added to the acetanilide mix.

 

As far as I know, the use of glacial acetic acid is to keep a low percentage of water, and thus, prevent hydrolysis, but this can be achieved using only the concentrated sulfuric acid.

 

So, why is (glacial) acetic acid needed?