Synthesis of Methyl Carbamates from Primary Aliphatic Amines and Dimethyl Carbonate in Supercritical CO<sub>2</sub>: Effects of Pressure and Cosolvents and Chemoselectivity
作者:Maurizio Selva、Pietro Tundo、Alvise Perosa、Federico Dall'Acqua
DOI:10.1021/jo0477796
日期:2005.4.1
selectivity is observed with polar protic media (i.e., MeOH), plausibly because of solvation effects (through H-bonds) of RNHCO2- moieties. The reaction shows also a good chemoselectivity: bifunctional aliphatic amines bearing either aromatic NH2 or OH substituents [XC6H4(CH2)nNH2, X = NH2, OH; n = 1, 2], undergo methoxycarbonylation reactions exclusively at aliphatic amino groups and give the corresponding
在130°C下,在CO 2(5-200 bar)存在下,脂肪族伯胺与碳酸二甲酯(MeOCO 2 Me,DMC)反应生成氨基甲酸甲酯(RNHCO 2 Me)和N-甲基化副产物(RNHMe和RNMe 2)。CO 2的压力在很大程度上影响反应转化率和对氨基甲酸酯的选择性:通常,转化率在中压(40 bar)时经历最大值(70-80%),并在低压和高压下下降,而选择性则是连续的压力的增加使压力从50%提高到90%。这是由CO 2在(i)与脂肪族胺的酸/碱平衡,(ii)RNHCO 2的反应性/溶解度中的多重作用来解释的。-具有/在DMC中的亲核试剂,和(iii)抑制底物的竞争性N-甲基化反应。助溶剂也影响反应:特别是,在选择性的下降与极性质子介质(即,甲醇)观察的振振有词因为RNHCO的溶剂化作用(通过H-键),2 -部分。该反应还显示出良好的化学选择性:带有芳族NH 2或OH取代基的双官能脂族胺[XC