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 degrees C, and form I subsequently recrystallized from this melt. Similarly, form III melts at 145 degrees C and then recrystallizes to form I. We also investigated the influence of the crystallization solvent on sulindac crystal shape.