THERMODYNAMIC NITRATION RATES OF AROMATIC-COMPOUNDS - PART 4 - TEMPERATURE-DEPENDENCE IN SULFURIC-ACID OF HNO3-]NO2+ EQUILIBRIUM, NITRATIONRATES AND ACIDIC PROPERTIES OF THE SOLVENT

The protonation-dehydration equilibrium of nitric acid (HNO3 + H+ reve rsible arrow H2O + NO2+) has been studied in the range 80-94 wt% H2SO4 as a function of temperature and the variations of [NO2+]/[HNO3] rati os have been analysed to evaluate the dissociation constants (pKNO(2)( +)) and the enthalpy of dissociation of the process. The nitration rat es of some aromatic compounds, related both to the stoichiometric conc entration of nitric acid (rate = k(2obs)[Ar][HNO3]) and to the effecti ve concentration of electrophilic species (rate = k(2)degrees[Ar][NO2]), have been investigated in the range 50-100 wt% H2SO4 and the depen dence upon acidity and temperature of the different rate profiles is d iscussed. Activation energies determined by k(2obs) and k(2)degrees ni tration rates are reported. The k(2)degrees values are found to be ind ependent of medium acidity and allow one to obtain consistent activati on energies as expected for activated and deactivated aromatic substra tes as well as for an encounter limited reaction. Equilibria and rates in sulfuric acid have been analysed using the Me activity coefficient functions whose values have been estimated over a range of temperatur e between 25 degrees C and 90 degrees C, The general trend observed in the acidic properties of the medium is reported. It is shown that the temperature has a small influence on the Mc function.