Monohydrated sibutramine hydrochloride is a widely used active ingredient for the treatment of obesity. An anhydrous form of sibutramine hydrochloride was prepared starting from its monohydrate form upon heating it at 1408C for 15 min. This dehydration process was monitored using conventional TG/DSC methods. Heated above 1908C, sibutramine hydrochloride sublimes and recrystallizes on the cold walls of the test tube, giving platelet shaped crystals suitable for single crystal X-ray diffraction analysis: monoclinic,
At variance, sibutramine free base was typically recovered as a viscous oily material, upon treatment of its hydrochloride salt in ethyl acetate solution. Recrystallization from hexane yielded a white polycrystalline powder, the structure of which was determined by unconventional ab initio X-ray powder diffraction analysis: triclinic, P-1, a ΒΌ 8.6578(3) A Λ, b ΒΌ 9.3318(3) A Λ, c ΒΌ 11.1224(4) A Λ, a ΒΌ 110.434(3)8, b ΒΌ 100.159(3)8, g ΒΌ 89.201(2)8, V ΒΌ 827.76(5) A Λ3, Z ΒΌ 2. Sibutramine, in its different crystalline environments, was also fully characterized by solid state 13 C NMR analyses. Additional spectral information was obtained by collecting spectra of a metastable, oily sample, before it slowly recrystallizes (within hours).