Stability and Ring-Shift Tautomerization of Cyclic Anhydrides of Benzenehexasulfonic Acid

Abstract

Upon heating in a dry atmosphere, benzenehexasulfonic acid forms three cyclic anhydrides. Mono- and dianhydride do not hydrolyze readily due their flatter structures compared to the hydrolysis products. The trianhydride appears more to be reactive toward hydrolysis. In solutions, the mono- and dianhydride undergo ring-shift tautomerization, which is in the latter case shifted toward the para isomer.

Hypersulfonated polyelectrolytes: preparation, stability and conductivity

“…Moreover, intra-and intermolecular reactions to form anhydrides and cyclic sulfones during heating has previously been reported in hexasulfonated benzenes, and this most probably also occurred in S125 resulting in a reduced concentration of free acid. 27 SEC analysis of the samples in the H + form showed a reasonably high molecular weight, and the density was 1.63-1.64 g cm −3 for both S125 and S142 (Table 1).…”

“…groups of S125 was in line with the discrepancy between the theoretical and experimental IEC values, as previously discussed. 27 The proton conductivity of pressed pellets of S125 and S142 was measured by electrical impedance spectroscopy in the temperature range T = 120-140 °C at a constant absolute water vapor pressure of 1 atm 10 and was compared with that of S220. This corresponds to a RH between approximately 20% and 50% at the respective temperature.…”