Reactions of Aryl Phenylacetates with Secondary Amines in MeCN. Structure−Reactivity Relationship in the Ketene-Forming Eliminations and Concurrent E2 and E1cb Mechanisms
作者:Bong Rae Cho、Yong Kwan Kim、Choon-Ock Maing Yoon
DOI:10.1021/ja961294k
日期:1997.1.1
the leaving group from 4-nitrophenoxide to 2,4-dinitrophenoxide. The results are consistent with an E2 mechanism and a reaction coordinate with a large horizontal component corresponding to proton transfer. When the base−solvent system is changed from R2NH−MeCN to R2NH/R2NH2+−70 mol % MeCN(aq), the Bronsted β, ρH, and |βlg| decrease. Finally, the ketene-forming elimination reactions from p-nitrophenyl
已经对 MeCN 中由 R2NH 促进的芳基乙酸 1 和 2 的芳基酯的消除反应进行了动力学研究。反应是二级反应,表现出 β = 0.44−0.84,|βlg| = 0.41−0.50,ρH = 2.0−3.6。布朗斯台德β和|βlg| β-芳基取代基的吸电子能力降低。Hammett ρH 值几乎保持不变,但 |βlg| 值随着基础强度变弱而增加。随着离去基团从 4-硝基苯氧基变为 2,4-二硝基苯氧基,ρH 和 β 均降低。结果与 E2 机制和具有对应于质子转移的大水平分量的反应坐标一致。当碱-溶剂系统从 R2NH-MeCN 变为 R2NH/R2NH2+-70 mol % MeCN(aq) 时,Bronsted β、ρH 和 |βlg| 减少。最后,