Phenolysis and aminolysis of 4-nitrophenyl and 2,4-dinitrophenyl S-methyl thiocarbonates in aqueous ethanol
作者:Enrique A. Castro、Margarita E. Aliaga、Marjorie Cepeda、José G. Santos
DOI:10.1002/kin.20562
日期:2011.7
linear with slope (β) values in the 0.5–0.7 range, in accordance with concerted mechanisms. Comparison of the SA aminolysis of 1 with the same one carried out in water shows that the change of solvent from water to aqueous ethanol destabilizes the zwitterionic tetrahedral intermediate, changing the mechanism from stepwise to concerted. This destabilization is greater than that due to the change from SA
的反应小号甲基ø - (4-硝基苯基)硫代碳酸酯(1)和小号甲基ø - (2,4-二硝基苯基)硫代碳酸酯(2)具有一系列次级脂环族(SA)的胺和酚经受动力学研究。在亲核试剂过量的情况下,获得伪一级速率系数(k obs)。在恒定pH下,相对于游离亲核试剂浓度的k obs曲线与斜率k N呈线性关系。Brønsted图(log k N与亲核试剂p K a)的反应是线性的,根据协调的机理,其斜率(β)值在0.5–0.7范围内。SA 1的氨解与在水中进行的SA氨解的比较表明,溶剂从水变为乙醇水溶液会破坏两性离子四面体中间体的稳定性,从而将机理从逐步转变为一致。该去稳定作用大于由于SA胺变为喹啉核苷而引起的去稳定作用。对于酚醛反应,k N乙醇水溶液中的值小于水中相同反应的值。考虑到亲核试剂是阴离子,该结果是出乎意料的,因为阴离子应在极性更大的溶剂中更稳定。该结果由以下事实解释:酚盐反应物具有在芳环中离