Reaction of succinic acid with ammonia
From Synthesis of Succinimide on Thomas' Chemistry:


  Add 186 g of succinic acid to RBF, place the beaker in an ice bath and start adding 220 ml of 26% ammonia slowly. Assemble short path distillation without a condenser, add some boiling chips. Heat the mixture under a small flame to distil of all the water. When the temperature reaches over 100°C the mixture darkens. Switch the receiver and collect everything that comes off before yellow fumes temp 280-300°C. Cool down to room temperature and place the receiver into a freezer for 24h, recrystallize the crude succinimide in hot ethanol. Then filter the crystals and wash with 40 ml of cold ethanol.


(Note that RBF = round-bottom flask)



The catch is that the amide can attack itself to close the ring, forming succinimide.

There are two rounds of amidification via a nucleophilic addition/elimination mechanism.