Question

What is the role of acetic acid in a bromination reaction with anisole?

Answer 1

It's just a solvent to dissolve anisole (both are polar). That is, if you meant glacial (anhydrous) acetic acid. It's also easily removed in an aqueous workup, given that it is polar and thus should dissolve in water.

Anisole is a benzene ring containing the methoxy group, which is an activating group (an ortho/para director) with respect to electrophilic aromatic substitution. Thus, the bromination reaction does not require `"FeBr"_3` to be the catalyst, when it would on plain old benzene.

So, your products would still be the ortho (1,2-) and para (1,4-) isomers of bromomethoxybenzene.