Correa NM, Durantini EN, Silber JJ
Departamento de Quimica y Fisica, Universidad Nacional de Rio Cuarto, Argentina.
J Org Chem. 2000 Oct 6;65(20):6427-33. doi: 10.1021/jo000714s.
The nucleophilic aromatic substitution (S(N)Ar) reaction between 1-fluoro-2,4-dinitrobenzene and piperidine (PIP) were studied in two different reverse micellar interfaces: benzene/sodium 1,4-bis(2-ethylhexyl) sulfosuccinate (AOT)/water and benzene/benzyl-n-hexadecyl dimethylammonium chloride (BHDC)/water reverse micellar media. The kinetic profiles of the reactions were investigated as a function of variables such as surfactant and amine concentration and the amount of water dispersed in the reverse micelles, W0 = [H2O]/[surfactant]. In the AOT system at W0 = 0, no micellar effect was observed and the reaction takes place almost entirely in the benzene pseudophase, at every AOT and PIP concentration. At W0 = 10, a slight increment of the reaction rate was observed at low [PIP] with AOT concentration, probably due to the increase of micropolarity of the medium. However, at [PIP] > or = 0.07 M the reaction rates are always higher in pure benzene than in the micellar medium because the catalytic effect of the amine predominates in the organic solvent. In the BHDC system the reaction is faster in the micellar medium than in the pure solvent. Increasing the BHDC concentration accelerates the overall reaction, and the saturation of the micellar interface is never reached. In addition, the reaction is not base-catalyzed in this micellar medium. Thus, despite the partition of the reactants in both pseudophases the reactions effectively take place at the interface of the aggregates. The kinetic behavior can be quantitatively explained taking into account the distribution of the substrate and the nucleophile between the bulk solvent and the micelle interface. The results were used to evaluate the amine distribution constant between the micellar pseudophase and organic solvent and the second-order rate coefficient of S(N)Ar reaction in the interface. A mechanism to rationalize the kinetic results in both interfaces is proposed.
研究了1-氟-2,4-二硝基苯与哌啶（PIP）在两种不同的反胶束界面中的亲核芳香取代（S(N)Ar）反应：苯/1,4-双（2-乙基己基）磺基琥珀酸钠（AOT）/水和苯/苄基正十六烷基二甲基氯化铵（BHDC）/水反胶束介质。研究了反应动力学曲线随表面活性剂和胺浓度以及反胶束中分散的水量W0 = [H2O]/[表面活性剂]等变量的变化情况。在W0 = 0的AOT体系中，未观察到胶束效应，且在每个AOT和PIP浓度下，反应几乎完全在苯假相中进行。在W0 = 10时，在低[PIP]下随着AOT浓度的增加，反应速率略有增加，这可能是由于介质微极性的增加。然而，当[PIP]≥0.07 M时，纯苯中的反应速率总是高于胶束介质中的反应速率，因为胺在有机溶剂中的催化作用占主导。在BHDC体系中，胶束介质中的反应比纯溶剂中更快。增加BHDC浓度会加速整体反应，且从未达到胶束界面的饱和状态。此外，该胶束介质中的反应不是碱催化的。因此，尽管反应物在两个假相中分配，但反应有效地在聚集体的界面处发生。考虑到底物和亲核试剂在本体溶剂和胶束界面之间的分布，可以定量解释动力学行为。这些结果用于评估胶束假相和有机溶剂之间的胺分配常数以及界面中S(N)Ar反应的二级速率系数。提出了一种使两个界面的动力学结果合理化的机理。
