Effect of the temperature on a hydrate diclofenac salt

The salt Diclofenac/N-(2-hydroxyethyl) pyrrolidine when crystallizes from water forms a di-hydrate, which looses the crystallization water molecules on heating or in the presence of silica gel, undergoing a phase transition. The two processes were followed at room temperature, at 40 and 50 degrees C by thermal analysis and analyzing the dimensional parameters obtained by scanning electron microscopy as a function of the changes occurring in the solid state. The fractal dimension of the particle surface (DS) was determined for the di-hydrate, the anhydrate and the anhydrous forms: DS values are close together suggesting that the processes modify only slightly the external morphology of the particles. The reactive dimension (DR) to dissolution suggests that the salt after the thermal treatment has a dissolution behaviour identical to that observed for the salt obtained from organic solvents. The two processes de-hydration and phase transition can be carried out at relatively low temperature, suggesting an important pathway to obtain the anhydrous form starting from the di-hydrate one.