Raman and kinetic evidence of NO2+ ion in solid acid catalyst

Samples of H2SO4/SiO2 loaded with HNO3 and analysed by Raman spectroscopy exhibit the band of the NO2 + ion, which is formed by the protonation-dehydration equilibrium of HNO3 in strong acidic media. The effectiveness of NO2 + as a nitrating species is tested in the nitration of aromatic compounds towards substrates with high acid requirements for the conversion reagents-products. The acidic properties of the acid systems used as catalysts are also described, and the thermodynamic parameters related to the acid-base proton transfer process are discussed.