Ketaki Nalawade Use a strictly nitrogen‑free, non‑nucleophilic solvent and catalyst system (i.e., eliminate ammonia/amines), ensuring dry conditions and inert catalyst to prevent imidation and favor maleic anhydride over maleimide.

Not sure how this is an oxidation reaction when what you propose is a conversion of maleic anhydride (with an O) to maleimide. (N) . The oxidation state is the same (!) and not a side reaction unless you are asking how to prevent reaction at the anhydride while you are reacting the molecule in question with an amine. If that's the case then the reaction of the amine first on the free diacid and then the anhydride should be made.

Not sure what you are asking. What are the specific reaction conditions, starting material and desired end product?