On the acidity of liquid and solid acid catalysts. Part 2. A thermodynamicand kinetic study for acid-catalysed nitrations

Solid acids prepared by adding sulfuric acid on silica gel have been used a s catalysts in the nitration of nitrobenzenes and their properties have bee n tested by kinetic studies at 25 degrees C. Nitration rates in concentrate d aqueous solutions of sulfuric acid were also analysed and the catalytic e fficiencies of sulfuric acid in liquid and solid phase were compared by usi ng kinetic data of analogous compounds. The results show that the solid aci d samples exhibit nitrating properties very similar to those observed in co ncentrated aqueous solutions of sulfuric acid (range of 90 wt%). The relati onship between nitration rates and effective concentration of electrophilic species [NO2+], determined by studying the protonation-dehydration equilib rium of nitric acid in strong acids (HNO3 +H+ reversible arrow H2O +NO2+), was tested to better understand the acidity properties of medium.