Study On Catalytic And Selective Synthesis Of Nitro-dimethylbenzene

The regioselective preparation of nitro-dimethylbenzenes was present in thispaper. The reaction was catalyticallycarried out in nitric acid/acetic anhydride,nitric acid， and nitrogen dioxide/molecular oxygen nitrating systems,respectively. It was found that the nitration process using65%nitric acid asnitrating reagent and acetic anhydride as the solvent over various solid acidcatalysts as compared with those of mineral acids appear to be the mostattractive and promising in the selective synthesis of nitro-dimethylbenzene.The isomer ratio of4-nitro-o-xylene to3-nitro-o-xylene could reach4.65whenthe reaction was conducted in acetic anhydride using5.0mmol o-xylene and10mmol65%nitric acid in the presence of0.95g HBEA-500at roomtemperature. A comparative nitration of m-xylene under similar conditions wasalso described. The isomer ratio of4-nitro-m-xylene to2-nitro-m-xylene couldreach8.1in high yield (98.3%). Furthermore, o-xylene reacted with nitrogendioxide/molecular oxygenover zeolite HBEA with Si/Al=500at35℃to yieldmononitro-o-xylenes as the main products, where the4-nitro-o-xylene isomerpredominated up to89%and the4-nitro-:3-nitro-o-xylenes isomer ratio wasimproved to7.8. Efficiency of recycled HBEA500in the preparation ofnitro-o-xylene and plausible mechanisms involving the catalytic nitration werealso discussed.