Despite the high profile of amphetamine, there have been relatively few structural studies of its salt forms. The lack of any halide salt forms is surprising as the typical synthetic route for amphetamine initially produces the chloride salt. (S)-Amphetamine hydrochloride [systematic name: (2S)-1-phenylpropan-2-aminium chloride], C9H14N(+)·Cl(-), has a Z' = 6 structure with six independent cation-anion pairs. That these are indeed crystallographically independent is supported by different packing orientations of the cations and by the observation of a wide range of cation conformations generated by rotation about the phenyl-CH2 bond. The supramolecular contacts about the anions also differ, such that both a wide variation in the geometry of the three N-H...Cl hydrogen bonds formed by each chloride anion and differences in C-H...Cl contacts are apparent. (S)-Amphetamine hydrobromide [systematic name: (2S)-1-phenylpropan-2-aminium bromide], C9H14N(+)·Br(-), is broadly similar to the hydrochloride in terms of cation conformation, the existence of three N-H...X hydrogen-bond contacts per anion and the overall two-dimensional hydrogen-bonded sheet motif. However, only the chloride structure features organic bilayers and Z' > 1.
Keywords: (S)-amphetamine salts; active pharmaceutical ingredients; crystal structure; organic bilayers; pharmaceuticals; salt screening.