Castro Enrique A, Gazitúa Marcela, Santos José G
Facultad de Química, Pontificia Universidad Católica de Chile, Casilla 306, Santiago 6094411, Chile.
J Org Chem. 2005 Sep 30;70(20):8088-92. doi: 10.1021/jo051168b.
[Chemical reaction: See text] The reactions of anilines with 4-nitrophenyl, 4-methylphenyl, and 4-chlorophenyl 4-nitrophenyl carbonates (BNPC, MPNPC and ClPNPC, respectively) are studied kinetically in 44 wt % ethanol-water, at 25.0 degrees C, with an ionic strength of 0.2 M (KCl). Plots of k(obsd) vs [amine] are linear, with the slopes (kN) independent of pH. The Brønsted-type plots (log k(N) vs pKa of conjugate acids of anilines) are linear, with slopes beta = 0.65, 0.85, and 0.78 for the reactions of anilines with BNPC, MPNPC, and ClPNPC, respectively. The values of the slopes for the two latter reactions are in accordance with those obtained in stepwise mechanism where breakdown to product of a zwitterionic tetrahedral intermediate is the rate-determining step. On the other hand, the beta value for the reactions of BNPC is at the upper limit of those found for concerted mechanisms. The kinetic results for the reactions of anilines with BNPC correlates well with those for the concerted reactions of the same amines with 4-methylphenyl and 4-chlorophenyl 2,4-dinitrophenyl carbonates: A plot of the calculated log k(N) values (through a multiple parametric equation) vs the experimental log k(N) values is linear with unity slope and zero intercept, which confirms the concerted mechanism for the latter three reactions.
[化学反应：见正文] 分别研究了苯胺与4-硝基苯基、4-甲基苯基和4-氯苯基4-硝基苯基碳酸酯（分别为BNPC、MPNPC和ClPNPC）在44 wt%乙醇-水体系中，25.0℃、离子强度为0.2 M（KCl）条件下的动力学反应。k(obsd) 对 [胺] 的作图呈线性，斜率（kN）与pH无关。布朗斯特型作图（log k(N) 对苯胺共轭酸的pKa）呈线性，苯胺与BNPC、MPNPC和ClPNPC反应的斜率β分别为0.65、0.85和0.78。后两个反应的斜率值与在逐步机理中得到的值一致，在该机理中两性离子四面体中间体分解为产物是速率决定步骤。另一方面，BNPC反应的β值处于协同机理所发现值的上限。苯胺与BNPC反应的动力学结果与相同胺与4-甲基苯基和4-氯苯基2,4-二硝基苯基碳酸酯的协同反应结果相关性良好：通过多重参数方程计算得到的log k(N) 值对实验log k(N) 值的作图呈线性，斜率为1，截距为0，这证实了后三个反应的协同机理。
