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.
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机译:Structure Determination and Mechanistic Insights of: I.Cyanobacteriochrome NpR6012g4 Light Sensor Protein in Phototaxis II.Retinal Degeneration 3 (RD3) Protein in Vision III.Ryanodine Receptor 2 (RyR2) Regulation by Calmodulin (CaM) in Cardiac Function =结构测定和机理洞悉:I.趋光性中的蓝细菌色素NpR6012g4光敏蛋白 II.视觉作用中的视网膜退化蛋白3 III.心脏功能中的钙调蛋白调控兰诺定受体2