THERMAL-BEHAVIOR OF MELT CRYSTALLIZED PHENYLBUTAZONE

In the DSC curves, the melting point of phenylbutazone Form A was affected by the heating rate (first heat cycle). The DSC curves of the melt crystallized phenylbutazone (second heat cycle) showed the endothermic peaks of both Form C and Form A. The change in the first heat cycle of either the heating rate, the upper temperature limit, or the isothermal hold period at the upper temperature limit affected the value of the area ratio between the endothermic peaks of the two polymorphs in the DSC curves of the melt crystallized phenylbutazone. It was therefore suggested that the value of the area ratio is related to the energy supplied to the melt phenylbutazone in the first heat cycle. According to this hypothesis, the energy level that the melt should reach to crystallize as the metastable Form C should be higher than the essential one to crystallize as the stable Form A.