Polymorphism of Sulindac: Isolation and Characterization of a New Polymorph and Three New Solvates

The polymorphism of sulindac was investigated. Two polymorphs (I and II) and a new crystalline form (form III) of sulindac were prepared by recrystallization in different solvents. In addition, three new pseudopolymorphs (solvates) from acetone, chloroform, and benzene were obtained, with each containing 1 mol of solvent to 2 mol of sulindac. Different sulindac polymorphs and pseudopolymorphs were characterized by X-ray diffractometry, infrared spectroscopy, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and hot-stage microscopy. The transition behavior of the crystalline forms of sulindac, their melting points, and their enthalpies were investigated by DSC. The melting of form II was observed at 184 °C, and form I subsequently recrystallized from this melt. Similarly, form III melts at 145 °C and then recrystallizes to form I. We also investigated the influence of the crystallization solvent on sulindac crystal shape.