SolutionsPreparation
1. Cyclic anhydrides
Why does succinic acid form its anhydride just on heating whereas acetic acid does not?
In succinic acid both carboxyl groups are in the same molecule and close a very favourable five-membered ring; with acetic acid the reaction is between two molecules and is much less favourable.
2. A mixed anhydride
How would you prepare acetic benzoic anhydride?
By treating sodium acetate with benzoyl chloride (or sodium benzoate with acetyl chloride): one of the acids must be activated as the chloride.
Heating a mixture of both acids would give a mixture of three anhydrides.