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 °C revealed how degradation pathways
change as a function of the oxidation state of the S center, as determined
by 1H 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.