X-ray structural studies and physicochemical characterization of the 1-butanol, 1-pentanol, and 1,4-dioxane solvates of succinylsulfathiazole.

The crystal structures and thermal decomposition of three solvated forms of the antibacterial drug succinylsulfathiazole (SST) have been studied. The solvates, with 1:1 host-guest stoichiometry, are SST x 1-butanol (1) SST x 1-pentanol (2), and SST x 1,4-dioxane (3). Solvates 1 and 2 crystallize in the triclinic system, space group P1, with two formula units per cell, and are nearly isostructural. The OH groups of the guest molecules in both solvates engage in hydrogen bonding to the host SST and occupy cavities in the crystals. Solvate 3 is triclinic, space group P1, with two formula units per cell, but the two independent solvent molecules are located in crystallographically distinct channels. In one channel, solvent molecules are hydrogen bonded to the host while, in the other, they are held by van der Waals interactions only. The structural results are in accord with thermogravimetric and differential scanning calorimetric data which indicate one-step desolvation for 1 and 2 but two-step desolvation for 3. X-ray powder diffraction was used to attempt identification of the polymorphic forms of SST resulting from desolvation of 1-3. Desolvation of 1 and 3 appears to yield pure polymorphs of SST while 2 yields a mixture of polymorphs. The activation energies for the desolvation of the nearly isomorphous solvates 1 and 2 were found by dynamic thermogravimetry to be 155 and 149 kJ mol(-1), respectively.