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首页> 外文期刊>RSC Advances >RANEY (R) nickel-catalyzed reductive N-methylation of amines with paraformaldehyde: theoretical and experimental study
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RANEY (R) nickel-catalyzed reductive N-methylation of amines with paraformaldehyde: theoretical and experimental study

机译：RANEY（R）镍催化的低聚甲醛对胺的还原N-甲基化：理论和实验研究

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RANEY (R) Ni-catalyzed reductive N-methylation of amines with paraformaldehyde has been investigated. This reaction proceeds in high yield with water as a byproduct. RANEY (R) Ni can be easily recovered and reused with a slight decrease of the yield. Using density functional theory (DFT), the mechanism of RANEY (R) Ni-catalyzed reductive N-methylation is discussed in detail. The reaction pathway involves the addition of amine with formaldehyde, dehydration to form the imine and hydrogenation. In the transition state of hemiaminal dehydration, the C-O bond cleavage of the aromatic amine is more difficult than that of the aliphatic amine. For the aromatic amine, a higher energy barrier must be overcome, which results in a relatively low yield. After addition of amine with formaldehyde and dehydration, imine is obtained and preferred to adsorb on the bridge site of the Ni(111) surface. The preferential pathways of imine hydrogenation involve the pre-adsorbed hydrogen atom attacking the nitrogen atom of the imine. The energy barrier of hydrogenation is much lower than that of addition and dehydration. Thus, the hydrogenation of imine is a relatively rapid reaction step. In the reductive N-methylation of secondary amine, the possible dehydration pathway is different from the one of the primary amine. In the dehydration of the secondary amine, the intermediate hemiaminal is initially adsorbed on the bridge site of the Ni(111) surface, then undergoes C-O bond cleavage, and eventually the hydroxyl is located in the bridge site. With the final hydrogenation, the product is obtained by adsorption on the top site of the Ni(111) surface.
机译：已经研究了RANEY（R）镍与多聚甲醛的胺还原N-甲基化反应。该反应以水作为副产物以高收率进行。 RANEY Ni可以很容易地回收和再利用，而收率略有下降。利用密度泛函理论（DFT），详细讨论了RANEY（R）Ni催化还原性N-甲基化的机理。反应途径包括胺与甲醛的加成，脱水以形成亚胺和氢化。在半胱氨酸脱水的过渡状态下，芳族胺的C-O键裂解比脂族胺的C-O键裂解更困难。对于芳族胺，必须克服更高的能垒，这导致相对较低的产率。在胺与甲醛加成并脱水后，获得了亚胺，并且优选吸附在Ni（111）表面的桥位上。亚胺加氢的优先途径涉及预吸附的氢原子攻击亚胺的氮原子。氢化的能垒远低于加成和脱水的能垒。因此，亚胺的氢化是相对快速的反应步骤。在仲胺的还原性N-甲基化中，可能的脱水途径不同于伯胺之一。在仲胺的脱水中，中间半缩醛首先被吸附在Ni（111）表面的桥位上，然后经历C-O键裂解，最后羟基位于桥位上。经过最终的氢化，通过吸附在Ni（111）表面的顶部获得产物。

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