Castro Enrique A, Campodonico Paola, Toro Alejandra, Santos José G
Facultad de Química, Pontificia Universidad Católica de Chile, Casilla 306, Santiago 22, Chile.
J Org Chem. 2003 Jul 25;68(15):5930-5. doi: 10.1021/jo034385q.
The reactions of anilines with 4-methylphenyl and 4-chlorophenyl 2,4-dinitrophenyl carbonates (MPDNPC and ClPDNPC, respectively) and the latter substrate with secondary alicyclic (SA) amines are subjected to a kinetic study in 44 wt % ethanol-water solution, at 25.0 degrees C, and an ionic strength of 0.2 M (KCl). The reactions are studied by following spectrophotometrically (360 nm) the release of 2,4-dinitrophenoxide anion. Under amine excess, pseudo-first-order rate coefficients (k(obsd)) are found. Plots of k(obsd) vs [amine] are linear and pH-independent, with slope k(N). The Brønsted-type plots (log k(N) vs pK(a) of aminium ions) are linear, with slopes beta = 0.68 and 0.66 for the reactions of anilines with MPDNPC and ClPDNPC, respectively, and beta = 0.44 for the reactions of SA amines with ClPDNPC. The magnitude of the slope for the latter reaction indicates that its mechanism is concerted. The slope values for the reactions of anilines are in the borderline between stepwise and concerted mechanisms. The sensitivity of logk(N) to the basicity of the nonleaving group (beta(nlg)) is ca. -0.7 for the reactions of anilines, in agreement with that found for the SA reactions (beta(nlg) ca. -0.6). These results suggest that the reactions of anilines are concerted, although it is also possible that both mechanisms (stepwise and concerted) operate simultaneously. By comparison of the reactions under investigation between them and with similar aminolyses, the following conclusions can be drawn: (i) ClPDNPC is more reactive than MPDNPC toward the two amine series. (ii) The change of water to aqueous ethanol destabilizes a zwitterionic tetrahedral intermediate. (iii) The change of the nonleaving group from MeO to 4-methylphenoxy or 4-chlorophenoxy also destabilizes this intermediate.
研究了苯胺与4-甲基苯基-2,4-二硝基苯基碳酸酯（MPDNPC）和4-氯苯基-2,4-二硝基苯基碳酸酯（ClPDNPC）的反应，以及后一种底物与脂环仲胺（SA）的反应，反应在44 wt%乙醇-水溶液中，25.0℃，离子强度为0.2 M（KCl）的条件下进行动力学研究。通过分光光度法（360 nm）跟踪2,4-二硝基苯氧阴离子的释放来研究反应。在胺过量的情况下，得到了准一级速率系数（k(obsd)）。k(obsd)对[胺]的作图是线性的且与pH无关，斜率为k(N)。布朗斯特类型的作图（log k(N)对铵离子的pK(a)）是线性的，苯胺与MPDNPC和ClPDNPC反应的斜率β分别为0.68和0.66，SA胺与ClPDNPC反应的斜率β为0.44。后一个反应的斜率大小表明其机理是协同的。苯胺反应的斜率值处于逐步机理和协同机理的边界。logk(N)对非离去基团碱性（β(nlg)）的敏感度，苯胺反应约为-0.7，与SA反应的情况（β(nlg)约为-0.6）一致。这些结果表明苯胺的反应是协同的，尽管也有可能两种机理（逐步和协同）同时起作用。通过比较所研究的反应之间以及与类似氨解反应的情况，可以得出以下结论：（i）ClPDNPC对这两个胺系列的反应活性比MPDNPC高。（ii）水变为乙醇水溶液会使两性离子四面体中间体不稳定。（iii）非离去基团从甲氧基变为4-甲基苯氧基或4-氯苯氧基也会使该中间体不稳定。
