Furosemide Solvates: Can They Serve As Precursors to Different Polymorphs of Furosemide?

In the present work, four solvates of furosemide with tetrahydrofuran S(THF), 1,4-dioxane S(DIOX), N,N-dimethylformamide S(DMF), and dimethylsulfoxide S(DMSO) were crystallized, the crystal structures were solved for S(THF), S(DIOX), and S(DMF). The existence of S(THF) and S(DMSO) was not reported before; for the previously known S(DIOX) and S(DMF), the crystal structures remained unsolved. The detailed structural analysis of furosemide containing crystal structures showed that the molecule of furosemide has a high conformational lability because of the rotations of the sulfamoyl and furanylmethylamino fragments. Some of the furosemide conformations were shown to be stabilized by the intramolecular N-H center dot center dot center dot Cl hydrogen bond. Desolvation of the four solvates was studied by TG and X-ray diffraction and was shown to give different products depending on the precursor and particle size: the desolvation of powder of S(THF) and the large crystals of S(THF), S(DIOX), and S(DMF) gives Form-III of furosemide, whereas powders of S(DIOX), S(DMF), and S(DMSO) give Form-I.