Solid acids as substitutes for sulfuric acid in the liquid phase nitration of toluene to nitrotoluene and dinitrotoluene

Abstract

Our results demonstrate that sulfuric acid supported on preshaped silica is a good catalyst for the nitration of toluene to dinitrotoluene using 65 wt.% nitric acid with respect to catalyst performance (activity, selectivity, regenerability) and catalyst handling (storage, stirring, separation). It is imperative to carefully control the water content of the catalyst prior to reaction in order to obtain high activity. The reusability of the catalyst without compromising performance has been demonstrated. Non-polar solvents seem to be required in order to prevent dissolution of the impregnated acid. Hence, the application of acetic anhydride as a solvent with potential water trapping ability was unsuccessful. Solvent-free operation is limited by the necessity to maintain a mixture that can be stirred. Hence, a maximum conversion of about 30% is achievable for the nitration of nitrotoluene to dinitrotoluene in one reaction cycle.