Nuclear magnetic resonance investigation of solutions of nitric acid and perchloric acid in water + dimethyl sulphoxide mixed solvents

Abstract

Solutions of nitric and perchloric acids in a mixed water + dimethyl sulphoxide (DMSO) solvent have been studied by proton magnetic resonance. Variations in solvent composition and acid concentration have little affect on the resonance of the methyl groups of the DMSO molecule, although the signal of the hydroxylic protons is considerably influenced by both factors. Chemical-shift data suggest that there is a prevalence of water protonation in an excess of water and that the amount of non-structured water freed by the acid decreases as the DMSO content increases, while in an excess of DMSO there is incomplete ionization of the acids and DMSO is preferably protonated. The signal of the hydroxylic protons broadens when the mole fraction of DMSO approaches unity in solutions of nitric acid, indicating a decrease in the rate of exchange among mobile protons.