Investigation of thermal behavior of enoxacin and its hydrochloride

The thermal behaviors of enoxacin and its hydrochloride under inert conditions were investigated by TG, FTIR, and TG/DSC-FTIR. The results indicated that the thermal behavior of enoxacin can be divided into three stages, while its hydrochloride consisted of four stages. The main difference lay in the sequence of decarboxylation and decarbonylation. For the enoxacin, the decarboxylation and decarbonylation occurred simultaneously, but for its hydrochloride, the two processes occurred in turn. The reason for this was the existence of hydrochloric acid in enoxacin hydrochloride, which changed its intermolecular force. The thermal analysis kinetic calculations of their first two stages were carried out, respectively. The apparent activation energy, pre-exponential factor, and the most probable model function were obtained using the master plots method. The results indicated that all these stages can be described by the model of nucleation and nucleus growing.