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To investigate the effects of solvent, the condensation reaction of benzaldehyde, dimedone, ethylacetoacetate, and ammonium acetate in various organic solvents at room temperature using 4.85 wt.% Ni0-nanoparticles as the catalyst was carried out. About 75% of the expectedproduct 4a was obtained when the solvent was ethanol. Obviously, thepolar solvents such as ethanol and acetonitrile [Table 2] were much better than non polar solvents. It was observed that in the presence ofsolvent the reaction takes more time to give high yields of product under similar ratio of the reactants. This may be due to the competitive adsorption of the solvent with the substrate molecule on the catalyst surface; hence reaction under solvent-free condition gives better yields in less time. The model reaction was carried out without any catalyst,but the product formation was in poor yield. Therefore, the catalyst plays an important role in the success of the reaction in terms of rate and yields of Hantzsch polyhydroquinoline derivatives. The reaction was also investigated with acid activated Mont. alone as catalyst and only a negligible amount of product formation was observed. Therefore, it is evident that supported Ni0 -nanoparticles are the active sites.

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1楼2014-09-25 10:30:35

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笔墨轻点: 金币+25, 翻译EPI+1, ★★★★★最佳答案 2014-09-25 20:20:29

为研究溶剂的作用，在室温条件下用各种有机溶剂和4.85%（重量百分比）的Nio纳米颗粒作为催化剂对苯甲醛，双甲酮，乙酰乙酸乙酯和醋酸铵进行了缩合反应。当用乙醇为溶剂时，可以获得约75％的预期产物。显然，极性溶剂如乙醇和乙腈[表2]均明显优于非极性溶剂。据观察，在反应物比例相似的条件下，有溶剂存在时反应需要更多时间以得到高产物产率。这可能是由于溶剂与催化剂表面上底物分子的竞争吸附作用; 因此，无溶剂条件下反应，在更短的反应时间内能够得到更好的产率。在没有任何催化剂存在的模型反应，形成产物的产率低。因此，催化剂在合成Hantzsch多聚羟基喹啉衍生物的反应中，不管在反应速率还是产率方面的成功都发挥重要作用。同时还以酸活化蒙脱石为催化剂单独使用，研究了反应情况，结果产物产量可以忽略不计。显而易见，支持的Nio纳米颗粒是活性位点。

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