The reaction of primary aromatic amines with alkylene carbonates for the selective synthesis of bis-N-(2-hydroxy)alkylanilines: the catalytic effect of phosphonium-based ionic liquids
作者:Maurizio Selva、Massimo Fabris、Vittorio Lucchini、Alvise Perosa、Marco Noè
DOI:10.1039/c0ob00105h
日期:——
At T ≥ 140 °C, different primary aromatic amines (pX–C6H4NH2; X = H, OCH3, CH3, Cl) react with both ethylene- and propylene-carbonates to yield a chemoselective N-alkylation process: bis-N-(2-hydroxyalkyl)anilines [pX–C6H4N(CH2CH(R)OH)2; R = H, CH3] are the major products and the competitive formation of carbamates is substantially ruled out. At 140 °C, under solventless conditions, the model reaction of aniline with ethylene carbonate goes to completion by simply mixing stoichiometric amounts of the reagents. However, a class of phosphonium ionic liquids (PILs) such as tetraalkylphosphonium halides and tosylates turn out to be active organocatalysts for both aniline and other primary aromatic amines. A kinetic analysis monitored by 13C NMR spectroscopy, shows that bromide exchanged PILs are the most efficient systems, able to impart a more than 8-fold acceleration to the reaction. The reactions of propylene carbonate take place at a higher temperature than those of ethylene carbonate, and only in the presence of PIL catalysts. A mechanism based on the Lewis acidity of tetraalkylphosphonium cations and the nucleophilicity of halide anions has been proposed to account for both the reaction chemoselectivity and the function of the catalysts.
在T ≥ 140 °C时,不同的氨基芳烃(pX–C6H4NH2;X = H, OCH3, CH3, Cl)与乙烯碳酸酯和丙烯碳酸酯反应,产生了化学选择性的N-烷基化过程:双-N-(2-羟基烷基)苯胺[pX–C6H4N(CH2CH(R)OH)2;R = H, CH3]是主要产品,同时竞争性形成碳酸酯的可能性大大降低。在140 °C下,在无溶剂条件下,苯胺与乙烯碳酸酯的模型反应通过简单混合化学计量的反应物而达到完成。然而,一类磷阳离子液体(PILs),如四烷基磷铵卤化物和托烷基物,证明对苯胺和其他氨基芳烃均为活性有机催化剂。通过13C NMR光谱监测的动力学分析表明,溴化物交换的PILs是效率最高的系统,能使反应加速超过8倍。丙烯碳酸酯的反应发生在比乙烯碳酸酯更高的温度下,并且仅在PIL催化剂的存在下进行。已经提出了一种基于四烷基磷铵阳离子的路易斯酸性和卤离子的亲核性的机制,以解释反应的化学选择性和催化剂的功能。