Chemistry of alkenyl azlactones. VII. Preparation and properties of multiazlactones derived from mercaptan‐functional compounds and oligomers

The reaction of polymercaptans and 2-alkenyl azlactones has been further investigated, and several new multiazlactones which are liquids at room temperature have been prepared and characterized. Michael addition yielding the multiazlactones was found to take place slowly in the absence of and rapidly in the presence of acid catalysts. If basic impurities capable of forming mercaptide ion were present, however, the reaction underwent a substantially different course producing primarily ring-opened products. A source of these basic impurities was determined to be the method of preparation of the alkenyl azlactone itself. When the azlactone was prepared from its acyclic N-substituted aminoacid precursor by cyclodehydration by use of ethyl chloroformate and triethylamine, a small amount of triethylamine remained that dramatically altered the course of reaction. Nonbasic cyclodehydration agents such as dicyclohexylcarbodiimide were effective at eliminating this side reaction, as well as was the practice of adding excess acid to the reaction system to neutralize the basic impurities.