On the acidity of liquid and solid acid catalysts. Part 3. Esterification of benzoic and mesitoic acids

Abstract

Methyl esters of benzoic and mesitoic acid have been prepared with high yields (>98 wt%) from the corresponding carboxylic acids + methanol in aprotic solvents over samples of H2SO4/SiO2 at 60°C. The results show a high catalytic efficiency of the solids but also suggest an acid strength comparable to that observed in concentrated aqueous H2SO4 (range >90 wt%) when the acid requirements for the esterification of analogous compounds in aqueous acid solutions are taken into account. Indeed, different reacting species, i.e., ArC(OH) 2 + from benzoic acid and 2,4,6‐triMe‐ArC=O+ from mesitoic acid are involved in the esterification, but the mesitoyl cation can be formed and esterified in the acidity ranges between 92 and 98 wt% H2SO4.