Selective Syntheses Of Nitro Polysubstituted Mononuclear Aromatics

Nitro poly substituted aromatic compounds are widely used in the preparation of pharmaceuticals, dyestuffs, perfumes, high-energy materials, polymers, and their intermediates. Various nitration methodologies involving nitric acid/acetic anhydride, nitric acid, and nitrogen dioxide/molecular oxygen nitrating systems were conducted to nitrate poly substituted mononuclear aromatics, respectively, in order to improving the regioselectivity in nitration.It was found that a typical substrate,m-xylene, could be selectively nitrated up to 92.2% isomer ratio of 4-nitro-m-xylene in yield of 96.7% mono nitrated products using 95% nitric acid as nitrating reagent in acetic anhydride medium over various solid acid catalysts. Compared with those of mineral acids involving nitrosulfuric acids in the ratios of 45%-55%, the process appear to be the most attractive and promising in the selective synthesis of nitro polysubstituted mononuclear aromatics.Nitric acid could affect the preparation nitro polysubstituted mononuclear aromatics. The solid catalysts promoted conversion of substrate and synthetic yield. Furthermore, m-xylene reacted with nitrogen dioxide/molecular oxygen over zeolite HBEA of Si/Al=280 at mid conditions to yield mono nitro-m-xylenes as the main products, where the 4-nitro-m-xylene isomer predominated up to 91.6% and the nitro-m-xylenes yield was improved to 96.0%. A comparative nitration of other poly substituted aromatics under similar nitrating systems was described, and the reaction mechanism was also discussed in the selective preparation of the nitro compounds.