Thermoanalytical characterization of pseudopolymorphs of sulphadimidine and sulphadimidine-trimethoprim molecular complexes

In recrystallization experiments of sulphadimidine from water. dioxane: and their mixtures aimed at preparing the unstable hydrate. a non-stoichiometr ic solvate with dioxane C12H14N4O2S.1/5C4H8O2 and a pseudopolymorph with si milar X-ray powder diffraction and infrared absorption properties bur diffe rent thermal behaviour (DSC. TG) were isolated. In co-crystallization exper iments of trimethoprim and sulphadimidine, a monohydrate of the respective 1:2 molecular complex and a methanol solvate of the equimolecular complex w ere obtained from aqueous ethanol and anhydrous methanol. respectively. The thermal stability of both pseudopolymorphic complexes is reflected by the high DSC and TG onset temperatures of solvent escape from the crystal latti ce (T(e)approximate to 163 C and T(e)approximate to 144 C. respectively. fo r water and methanol) and is consistent with the important role of water in the hydrated crystal packing and the very strong hydrogen-bonding interact ion of methanol with a sulphonamido oxygen atom in the methanol solvate cry stal. (C) 1998 Elsevier Science B.V.