Examining the Alkaline Stability of Tris(dialkylamino)sulfoniums and Sulfoxoniums

Herein, a synthetic method was developed to prepare a series of tris(dialkylamino)sulfonium and sulfoxonium cations from sulfur monochloride. Alkaline stability studies of these two cation families in 2 M KOH/CD3OH solution at 80 degrees C revealed how degradation pathways change as a function of the increasing Alkaline Stability oxidation state of the S center, as determined by H-1 NMR spectroscopy. The sulfonium cations (S+(NR2)(3)) typically degrade by nucleophilic attack at the sulfur atom with loss of an amino group and a proton transfer reaction to produce sulfoxides, while the sulfoxoniums (O+=S(NR2)(3)) tend to degrade by loss of an R group to form sulfoximines. From the group of sulfoniums and sulfoxoniums explored in this work, the tris(piperidino)- sulfoxonium cation was noted to have excellent alkaline stability. This sulfoxonium should be suitable for future examination as a tethered cation in anion-exchange membranes (AEMs), or as a phase-transfer catalyst in biphasic reactions.