Simple and efficient one-pot solvent-free synthesis of N-methyl imines of aromatic aldehydes
作者:Niko S. Radulović、Ana B. Miltojević、Rastko D. Vukićević
DOI:10.1016/j.crci.2013.01.010
日期:2013.3
Résumé A one-pot solvent-free synthesis of N-methyl imines in good to excellent yields was performed by grinding together aromatic aldehydes and methylamine hydrochloride in the presence of a base. The best yields were achieved when an excess of methylamine hydrochloride and inexpensive sodium hydrogen carbonate was used (usually in a molar ratio ArCHO/CH3NH2·HCl/NaHCO3 = 1:5:5), allowing the reaction to proceed for 1 h (in the case of aromatic aldehydes containing electron-withdrawing substituents) or overnight (in the case of electron-rich aldehydes). After a simple work-up (extraction with diethyl ether) the obtained products were mostly pure enough for spectral characterization. In this way, 31 N-methyl imines were prepared, among which eight were synthesized for the first time. Their structures were elucidated by spectral means (1H- and 13C-NMR, IR, MS) whenever it was possible. In the case of salicylaldehyde and 4-chlorobenzaldehyde, the synthesis of the corresponding imines was also conducted on a gram-scale with a 72% and 84% isolated yield, respectively. The present approach not only provides good to high yields, but also eliminates the disadvantages of the traditional synthesis of N-methyl imines, such as the use of hazardous solvents and more or less expensive catalysts and the necessity of work/handling with an anhydrous gas in pressurized containers.
简述 在碱存在下,通过将芳香醛和盐酸甲胺研磨在一起,实现了 N-甲基亚胺的单锅无溶剂合成,收率从良好到极佳。当使用过量的盐酸甲胺和廉价的碳酸氢钠时(通常摩尔比 ArCHO/CH3NH2-HCl/NaHCO3 = 1:5:5),让反应进行 1 小时(如果是含有抽电子取代基的芳香醛)或过夜(如果是电子丰富的醛),可获得最佳收率。经过简单的处理(用二乙醚萃取)后,得到的产物大多纯度很高,足以进行光谱鉴定。通过这种方法,共制备出 31 种 N-甲基亚胺,其中 8 种是首次合成。在可能的情况下,通过光谱手段(1H-和 13C-NMR、IR、MS)阐明了它们的结构。对于水杨醛和 4-氯苯甲醛,也在克级规模上合成了相应的亚胺,分离收率分别为 72% 和 84%。本方法不仅产量高,而且消除了传统合成 N-甲基亚胺的缺点,如使用有害溶剂和或多或少昂贵的催化剂,以及必须在加压容器中使用无水气体工作/处理。