Synthesis Of Several Nitropyridines And Aminopyridines

Nitro and amino-pyridines are important chemical materials and intermediates, which have been widely used in pharmacy, energetic, and polymer-materials industry. With the development of China chemical industry, the compounds constantly have a broad application and optimistic market prospects. Therefore, the deep research about their synthetic routes are still in great desire. In order to get the target compounds with high purity and high yield, now the investigation were carried out from the nitrification and reduction.(1) Nitrification:The initial study was carried out using 2,6-diaminopyridine as the substrate to optimize the reaction conditions. Compared to other synthetic methods, the results showed that super-acid system was much better than the ordinary mixed acid, the yield to 90.0%. In this paper, nitrating agent of 20%SO₃ in H₂SO₄/fuming HNO₃ was also focused on. The effect of different factors were also investigated to find the optimum conditions, which were as follows: V_H2SO4:V_HNO3=5:1, M_DAP:M_HNO3=1:2.1, reaction temperature is 40℃, and the reaction time is 3 h. Under these conditions, a higher 92.5% yield of 2,6-diamino-3,5-dinitropyridine was obtained.2-amino-3-nitro-5-bromopyridine,4-amino-3-nitropyridine,4-amino-3,5-dinit ropyridine and 2,6-diamino-3,5-dinitropyrazine were synthesized by using the optimum reaction condition.(2) Reduction:The initial study was carried out using 2,6-diamino-3,5-dinitropyridine as the substrate to optimize the reaction conditions. The reduction was prepared by three methods. The target compound was not obtained with the iron or hydrazine hydrate methods. However, the catalytic hydrogenation was able to achieve more satisfactory results. The method of hydrogenation by using Raney Ni as the reducer was studied. The effect of different factors were investigated to find the optimum conditions, which were as follows:reaction solvent is ethanol, reaction temperature is 50℃, reaction pressure is 1.0～1.5 MPa, and the amount of catalyst is 10% (weight percent in nitropyridine compounds). Under these conditions, the yield of 2,3,5,6-thaminopyridine hydrochloric acid can reach to 89.0%. The reducer could be recycled for four times, through the treatment of sodium hydroxide solution, which save costs and have a good prospect for industrial application.