Selective Syntheses Of Nitro Polycyclic Aromatic Compounds

Nitro aromatic compounds are widly used as pharmaceuticals, high-energy materials, dyestuffs, perfumes, functional materials and their intermediates. The regioselective nitration of 4-bromobiphenyl and 4,4’-dimethylbiphenyl using nitric acid, nitric acid/acetic anhydride, and nitrogen dioxide/molecular oxygen as nitrating agents were respectively explored in the preparation of the nitro compounds. It is found that zeolite HBEA-25 both displayed better catalytic activities. Superior selectivity for production of 4-bromo-4’-nitrobiphenyl and higher mono-nitration yield were obtained among these nitration systems. When the reaction was conducted in nitrogen dioxide nitrating system, an optimization was as follow:2.0 mmol 4-bromobiphenyl,6.0 mmol liquid nitrogen dioxide and 0.35 g HBEA-25 was added in 1,2-dichloroethane and reacted at 40℃ for 10 h. The 4-bromo-4’-nitrobiphenyl to 4-bromo-2’-nitrobiphenyl ratio could reach 4.39 in high yield of 94.3%.For the nitration of 4,4’-dimethylbiphenyl, the satisfactory yield mono-nitration could be achieved by controlling of the reaction temperature, material ratio, catalyst dosage and reaction time. However, adding acetic anhydride facilitated dinitration of 4,4’-dimethylbiphenyl, which resuled in lower mononitraion yield and higher dinitration yield.For the dinitration of 4,4’-dimethylbiphenyl, it is found that the nitration process using 95% nitric acid as nitrating reagent and acetic anhydride as the solvent over various solid acid catalysts appeared to be more attractive. Under optimum conditions, the yield of dinitration was 78.5% and the isomer ratio in 2,3’-dinitro-: 3,3’-dinitro-4,4’-dimethylbiphenyl was improved to 3.80. Efficiency of recycled HBEA-25 and the catalytic mechanism in the nitration of 4-bromobiphenyl were also discussed.