Determination of the onset of crystallization of N1-2-(thiazolyl)sulfanilamide (sulfathiazole) by UV-Vis and calorimetry using an automated reaction platform; subsequent characterization of polymorphic forms using dispersive Raman spectroscopy

This work describes the use of UV/visible spectroscopy and calorimetry to follow the onset of crystallization of a commercially available compound, N 1-2-(thiazolyl)sulfanilamide (sulfathiazole), during crystallization reactions performed using an automated reaction platform. Sulfathiazole has been the subject of numerous publications through which considerable confusion about the morphic form is apparent. This work does not attempt to investigate exhaustively the polymorph issue, but rather to exploit the use of the HEL auto-MATE for monitoring the onset of crystal formation. Real-time calorimetry and UV-Vis spectroscopy are compared as tools for determining the onset of crystallization. Subsequently, differential scanning calorimetry, dispersive Raman, and infrared spectroscopy analysis serve to identify the crystal forms generated by the HEL auto-MATE. A solvent–anti-solvent matrix and several bench-top crystallization experiments were performed to supplement the investigation in terms of generating the desired polymorphs.