QUANTITATIVE RAMAN-SPECTROSCOPIC STUDIES OF NITRONIUM ION CONCENTRATIONS IN MIXTURES OF SULFURIC AND NITRIC-ACIDS

The intensity of the nu(NO) stretching band of NO2+ at DELTAnu = 1400 cm-1 in the Raman spectra of nitric acid-water-sulphuric acid mixtures has been studied to determine nitronium ion concentrations over the temperature range 293-313 K. The nitronium ion concentration in these mixtures was found to decrease with increase in temperature. The nitrating species for acid mixtures used in mono- and di-nitrations is consistent with nitronium ion, NO2+, but at a typical acid concentration of less than H2SO4:HNO3:H2O = 30:15:55 mole % used in industrial mononitrations, there is no spectroscopic evidence for the presence of NO2+. It is suggested that the nitrating species in these weaker acid solutions is the acid hydrate, H2NO3+, which is a weaker nitrating species than NO2+.