Preparation Of 1,5-dinitronaphthalene From Catalytic Nitration Of 1-nitronaphthalene With NO₂ Over Novel Solid Acid

Dinitronaphthalene is an important chemical intermediate,which can be widely used in dye processing and plastic material preparation.Polyurethane material prepared from 1,5-dinitronaphthalene as precursor has important application value because of its heat resistance and resilience.The traditional industrial production of 1,5-dinitronaphthalene mainly adopts the mixed acid method of nitric acid and sulfuric acid,in which concentrated nitric acid is the nitrating agent and concentrated sulfuric acid is the catalyst.However,this nitration process has some drawbacks,such as high acid use,serious environmental pollution and only about 35%selectivity of 1,5-dinitronaphthalene.In this paper,the efficient and stable solid acid catalysts were developed to replace the sulfuric acid catalyst for the nitration of 1-nitronaphthalene with high selectivity under mild conditions employing using green and economical nitrogen dioxide acid as a nitrating agent.The main conclusions of this paper are as follows:（1）The metal oxides catalysts were screened using a nitration system of nitrogen dioxide,oxygen,and acetic anhydride,and the cheap metal oxides Cu O/Zn O catalyst performed well.By optimizing the preparation conditions of the catalyst and under the optimal reaction conditions,the molar ratio of 1-nitronaphthalene to nitrogen dioxide was 1:4,the reaction temperature was 40°C,the pressure of oxygen was 0.7 MPa,the reaction time was 4 h,the dosage of catalyst was 0.5 g,the conversion of 1-nitronaphthalene was 98.4%and the selectivity of 1,5-dinitronaphthalene was 49.9%.The Cu O/Zn O catalyst demonstrated good stability after 5 cycles,with the conversion of 1-nitronaphthalene and selectivity of 1,5-dinitronaphthalene being nearly unchanged.The results indicated that the strong acid or strong acid sites of catalyst has an important effect on the nitration reaction.（2）The solid superacid catalyst S₂O₈^2-/Zr O₂ modified by Cu or Fe were screened.The solid superacid catalysts(S₂O₈^2-/Cu-Zr O₂ and S₂O₈^2-/Fe-Zr O₂)exhibited good catalytic performance.The preparation conditions of the catalyst were optimized,including oxide content,sulfur species impregnation and calcination temperature.When S₂O₈^2-/Cu-Zr O₂ was used,under the optimal conditions,the molar ratio of 1-nitronaphthalene to nitrogen dioxide was 1:4,oxygen pressure was0.7 MPa,reaction temperature was 35°C,reaction time was 5 h,the amount of catalyst was 0.4 g the conversion of 1-nitronaphthalene and the selectivity of 1,5-dinitronaphthalene were 97.0%and 54.9%respectively.When S₂O₈^2-/Fe-Zr O₂ was used,under the optimum reaction conditions,the molar ratio of 1-nitronaphthalene to nitrogen dioxide is 1:3,the oxygen pressure is 0.7 MPa,the reaction temperature is 40°C and the reaction time is 5 h,the conversion of 1-nitronaphthalene was 96.8%and the selectivity of 1,5-dinitronaphthalene was 62.6%.Both solid superacid catalysts showed good stability.The conversion of 1-nitronaphthalene and the selectivity of 1,5-dinitronaphthalene only decreased by 3%after the catalyst was recycled 5 times.The selectivity of 1,5-dinitronaphthalene was improved significantly by the synergistic catalysis of Lewis acid site and strong acid site.Therefore,the nitration system of nitrogen dioxide-oxygen-acetic anhydride was selected in this paper.The reaction conditions were mild,the selectivity of the target product was high,the environmental pollution was small and the cost was low.The prepared solid acid catalyst has excellent catalytic performance,good cycle stability and low cost in the nitration of 1-nitronaphthalene.This study provides a new idea for the preparation of 1,5-dinitronaphthalene with high selectivity,which has important theoretical significance and good application prospect.