Mechanistic understanding of the active intermediates of 2,6-diaminopyridine(DAP) dinitration in the concentrated nitric-sulfuric acid system is of crucial importance for the selectivity control of target product, i.e...Mechanistic understanding of the active intermediates of 2,6-diaminopyridine(DAP) dinitration in the concentrated nitric-sulfuric acid system is of crucial importance for the selectivity control of target product, i.e., 2,6-diamino-3,5-dinitropyridine(DADNP). The active intermediates determining the product selectivity are theoretically studied. The HSO_(4)^(-)-NO_(2)^(+) complex is proposed as the dominant active nitrating intermediate for the first time, which shows low energy barrier(i.e., 10.19 kcal·mol^(-1),1 kcal = 4.186 k J) for direct dinitration of DAP to DADNP. The formed water during the reaction results in not only the formation of less active SO_(4)^(2-)-NO_(2)^(+) complex, but also the occurance of DAP sulfonation(DAP-SO_(3)H intermediate)to facilitate the formation of mononitration byproduct. Meanwhile, the accompanied thermal effects cause the generation of undesirable pyridine-NHNO_(2) intermediate, which is difficult to be rearranged to yield DADNP, inhibiting the reaction and thus giving low DAP conversion. The insights reported here elucidates the importance of thermal effects elimination and water content control, confirmed experimentally in the batch-and micro-reaction systems.展开更多
基金financially supported by the National Natural Science Foundation of China, China (21922803, 22122807, and 22008072)the Innovation Program of Shanghai Municipal Education Commission, China+1 种基金the Program of Shanghai Academic/Technology Research Leader, China (21XD1421000)the China Postdoctoral Science Foundation, China (2020M671025 and 2019TQ0093)。
文摘Mechanistic understanding of the active intermediates of 2,6-diaminopyridine(DAP) dinitration in the concentrated nitric-sulfuric acid system is of crucial importance for the selectivity control of target product, i.e., 2,6-diamino-3,5-dinitropyridine(DADNP). The active intermediates determining the product selectivity are theoretically studied. The HSO_(4)^(-)-NO_(2)^(+) complex is proposed as the dominant active nitrating intermediate for the first time, which shows low energy barrier(i.e., 10.19 kcal·mol^(-1),1 kcal = 4.186 k J) for direct dinitration of DAP to DADNP. The formed water during the reaction results in not only the formation of less active SO_(4)^(2-)-NO_(2)^(+) complex, but also the occurance of DAP sulfonation(DAP-SO_(3)H intermediate)to facilitate the formation of mononitration byproduct. Meanwhile, the accompanied thermal effects cause the generation of undesirable pyridine-NHNO_(2) intermediate, which is difficult to be rearranged to yield DADNP, inhibiting the reaction and thus giving low DAP conversion. The insights reported here elucidates the importance of thermal effects elimination and water content control, confirmed experimentally in the batch-and micro-reaction systems.
