Thermodynamic Nitration Rates of Aromatic Compounds. Part 4. Temperature Dependence in Sulfuric Acid of HNO3 ->NO2+ Equilibrium, Nitration Rates and Acid Properties of the Solvent.

The protonation-dehydration equilibrium of nitric acid (HNO3+ H+===H2O+ NO2+) has been studied in the range 80-94 wt% H2SO4 as a function of temperature and the variations of [NO2+] / [HNO3] rations have been analysed to evaluate the dissociation constants (pK NO2+) and the entalpy of dissociation of the process. The nitration rates of some aromatic compounds, related both to the stoichiometric concentration of nitric acid (rate=k 2obs[Ar] [HNO3]) and to the effective concentration of electrophilic species (rate=k2* [Ar] [NO2+]), have been investigated in the range 50-100wt% H2 SO4 and the dependence upon acidity and temperature of the different rate profiles, is discussed. Activation energies determined by k 2obs and k2* nitration rates are reported. The k2* values are found to be independent of medium activity and allow one to obtain consistent activation energies as expected for activated and deactivated aromatic substrates as well as for an encounter limited reaction. Equilibria and rates in sulfuric acid have been analysed using the Mc activity coefficient functions whose values have been estimated over a range of temperature between 25*C and 90*C. The general trend observed in the acidic properties of medium is reported . It is shown that the temperature has a small influence on the Mc function.

MARZIANO N.C.;  TOMASIN A.;  TORTATO C.;  ZALDIVAR-COMENGES Jose' Manuel; 

1998-09-28

JRC16994

https://publications.jrc.ec.europa.eu/repository/handle/JRC16994,