Heating-Induced Phase Transition of Bupropion Hydrobromide Polymorphs

Abstract

Crystal phase transition and isothermal crystallization kinetics of bupropion hydrobromide is studied by thermal analysis, X-ray powder diffractometry, and scanning electron microscopy. As well known, bupropion hydrobromide has two stable polymorphic forms, form I and form II, during the production. Here it is found that form II will convert into form I with thermal treatment. Avrami exponent n is evaluated to be around 2.0 in the range 170°C-190°C, which indicates that the phase transition is a process of one-dimensional nucleation growth. This viewpoint is also confirmed by microscope morphology study. In addition, phase-transition active energy is calculated to be 239.4 kJ/mol, which means that a high energy barrier needs to be overcome to start up the phase transition.