Knoevenagel reactions have been covered here before, in many threads. It's well known that the reaction progresses faster and yields are usually better when the water that is formed by the reaction is removed, thus IMHO it would probably be best to start out with as dry of Ammonium Acetate as possible, though it isn't critical. Back in November, drying techniques using a vacuum with a reference for drying AA were brought up in a Methods Forum thread titled: Anhydrous or not.... by modesty In the future please use the search engine, it saves everyone a lot of time.