Reactivity of ethyl acetate and its derivatives toward ammonolysis: Ramifications for ammonolysis-based microencapsulation process

The reactivity of three ester organic solvents toward ammonolysis was examined in relation to the development of an ammonolysis-based microencapsulation process. Ethyl acetate, ethyl chloroacetate, and ethyl fluoroacetate were chosen as ester organic solvents. Progesterone was considered as a model drug to be encapsulated into poly-D,L-lactide-co-glycolide microspheres. A polymeric dispersed phase was emulsified in an aqueous phase, to which ammonia was added to initiate ammonolysis. The polarization status of a carbonyl group in the backbone of the ester was found to decide the magnitude of the ester reactivity. In fact, the simple ester ethyl acetate hardly reacted with ammonia, while ethyl chloroacetate and ethyl fluoroacetate showed greater reactivity toward ammonolysis. The rapid completion of ammonolysis led to the conversion of the water-immiscible solvents into water-soluble solvents, thereby providing an efficient tool for microsphere solidification. Among microencapsulation parameters, the type of dispersed solvent, the molar ratio of ammonia to a dispersed solvent, and the percentage of the progesterone payload decisively influenced the characteristics of the microspheres. Subsequently, variations in such parameters accom-panied considerable influence on microsphere morphology, incorporation efficiency, thermal behavior, the degree of residual solvents, and the physical status of progesterone. Optimization of the process parameters would not only contribute to improving the ammonolysis-based microencapsulation process, but would also permit the tailoring of microsphere properties to specific demands.