3-(N-Alkylammonium)propanesulfonate Inner Salts, A Short Series

Reaction of even parity primary alkyl amines with propanesultone produces 3-(N-alkylammonium)propanesulfonate inner salts as slightly-soluble solids in polar solvents and in good yields. A short series of amines, n-C_nH_2n+1NH₂ with n = 4, 6, 8, 10, was studied. Crystals of the N-butyl analog from water occurred as a dihydrate, orthorhombic, P nma, with molecules lying on mirror planes and waters in general positions. Secondary ammonium ions are hydrogen-bonded to waters of crystallization, which are hydrogen-bonded to sulfonate oxygens with only two-centered⁺N-H…O_w and O-H…O^- interactions. Beginning with the N-hexyl homolog, crystals are polycrystalline, fibrous and with sufficient alignment coherence to allow determination as though single crystals. The degree of fiber misalignment was 3–5^o, approximately. Crystals from water are triclinic (unsolvated), P -1, with molecules lying between crystal (0 2 2) planes. Molecular packing shows adjacent molecules hydrogen-bonded between secondary ammonium ions and sulfonate ions in which all ⁺N-H…(O, O’)^- interactions are three-centered. Terminal alkyl groups pack in adjacent regions so that both hydrogen-bonding and dispersion attractions contribute to increasing intermolecular attractions and melting temperatures, exceeding 260 ^oC for the N-decyl homolog. The four compounds are further characterized by infrared spectroscopy and proton and carbon magnetic resonance spectroscopy and solubilities in common solvents.

Graphical Abstract

3-(N-Butylammonium)propanesulfonate zwitterions are mirror symmetric in P nma, while hexyl, octyl and decyl homologs are fibrous triclinic (P -1) structures with molecules lying approximately along the (0 1 1) planes