Reactions of nitronium sulfates: Hunting for dinitro sulfate

Abstract

AbstractNearly 70 years ago, it was shown that the reaction between equimolar amounts of SO3 and N2O5 results in dinitronium disulfate (NO2)2S2O7 rather than monosulfate (NO2)2SO4. Because SO3 can dimerize, it was believed for long that this feature is the main cause of the formation of nitronium disulfate. Then, it was discovered that the reaction of NOSO3Cl with N2O5 results in dinitronium disulfate, and (NO2)2SO4 was suggested as an intermediate. The development of Raman spectroscopy made it possible for us to solve the fundamental problem of the existence of an elusive dinitro sulfate. The inevitability of dinitro sulfate formation was demonstrated by the transformations of nitronium sulfates (NO2)2S2O7, NO2HSO4, and (NO2)[CF3C(O)OSO3], and the Raman spectroscopy technique has shown the presence of the compound in the solid reaction products. In order to establish the structure of solid dinitro sulfate, quantum chemical calculations of the nitro ester form (O2NOSO3NO2) and of the [OSO3NO2]− anion were performed, but the conclusions about the diionic structure [NO2]+2[SO4]2− were made only due to the synthesis of the related nitronium sulfates K (NO2)SO4 and K (NO2)S2O7 whose Raman spectra were compared with that of dinitro sulfate. The decomposition pathways of all these unstable molecules were established. Reactions of nitronium disulfates, (NO2)2S2O7 or (NO2)[CF3C(O)OS2O6], with CF3COOH showed that, unlike HNO3, the organic acid does not destroy the sulfate chains but can substitute terminal groups including nitronium ion. So the chemistry of nitronium monosulfates was studied for the first time, and the existence of an unstable dinitronium sulfate was proved using Raman spectroscopy.