Many derivatives of industrially useful cellulose have hydroxyls of the anhydroglucose(AHG) units uncompletely substituted. Since each AHG unit of a cellulose molecule is a trihydric alcohol,consisted of one primary(p...Many derivatives of industrially useful cellulose have hydroxyls of the anhydroglucose(AHG) units uncompletely substituted. Since each AHG unit of a cellulose molecule is a trihydric alcohol,consisted of one primary(position 6) and two secondary hydroxyl groups(positions 2 and 3), the distribution of substituents in these trihydric alcohol units could be different for different derivatives. The展开更多
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
There was a complete set of cross-polar distributive data of nitrate （NO<sub>3</sub><sup>-</sup>） content inthe surface snow of the Antarctic ice sheet along the route of the 1990 Internation...There was a complete set of cross-polar distributive data of nitrate （NO<sub>3</sub><sup>-</sup>） content inthe surface snow of the Antarctic ice sheet along the route of the 1990 International Trans-Antarctica Expedition. We have shown the profiles of nitrate concentration and flux alongthe route as the plots associated with geomagnetic latitude for further analysis on the展开更多
文摘Many derivatives of industrially useful cellulose have hydroxyls of the anhydroglucose(AHG) units uncompletely substituted. Since each AHG unit of a cellulose molecule is a trihydric alcohol,consisted of one primary(position 6) and two secondary hydroxyl groups(positions 2 and 3), the distribution of substituents in these trihydric alcohol units could be different for different derivatives. The
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.
基金Project supported by the National Committee for Antarctic Research of China, the State Commission of Science and Technology of China, and the National Natural Science Foundation of China.
文摘There was a complete set of cross-polar distributive data of nitrate （NO<sub>3</sub><sup>-</sup>） content inthe surface snow of the Antarctic ice sheet along the route of the 1990 International Trans-Antarctica Expedition. We have shown the profiles of nitrate concentration and flux alongthe route as the plots associated with geomagnetic latitude for further analysis on the
