Kinetics of Polymorphic Transformation of Sulfathiazole Form I

A quantitative method is presented which utilizes differential scanning calorimetry for the determination of sulfathiazole Form I in the presence of sulfathiazole Form 11. Data are included which demonstrate that the method can be utilized to follow the rate of transformation of Form 1 to Form 11. The kinetics for this transition have been described as being somewhat analogous to diffusion-controlled crystal growth from solution. An activation energy of 56 kcal./mole was calculated for the system. This value was in agreement with the activation energy obtained using a differential thermal method.