The catalytic efficiency of 10-amino[20]paracyclophane in the deacylation of p-nitrophenyl carboxylates was investigated in 10.9 or 20.8% (v/v) aqueous ethanol at μ=0.10 (KCl). The present catalyst exhibited marked catalytic effects not only in the free amine but in the ammonium form. The observed saturation-type kinetics is consistent with a reaction mechanism which involves pre-equilibrium complexation between the aminoparacyclophane and the substrate at a 1 : 1 molar ratio, followed by pseudo-intramolecular catalysis effected by the amino group of the macrocycle. Studies on the inhibition effect by 1-dodecanol and the modification of the catalyst by 2,4-dinitrofluorobenzene confirmed the effective binding ability of the present paracyclophane toward hydrophobic substrates. The free amine form of the catalyst acted as an effective nucleophile to give the acylated aminoparacyclophane as confirmed by the product analysis. On the other hand, the protonated amine form also enhanced the ester degradation, retaining a turnover behavior. On the basis of the kinetic solvent isotope effect and the exceedingly minor kinetic effect of [10-oxo[20]paracyclophan-22(23)-ylmethyl]trimethylammonium chloride in the ester degradation in the neutral pH region, a plausible reaction mechanism has been discussed.
在10.9%或20.8%(v/v)
乙醇水溶液中,研究了10-
氨基[20]对环
烷烃在脱酰化对
硝基苯基
羧酸酯反应中的催化效率,μ=0.10(KCl)。现在的催化剂在游离胺和
铵形式中均表现出显著的催化效果。观察到的饱和型动力学与一种反应机制相一致,该机制涉及胺基对环
烷烃与底物之间的1:1摩尔比的前平衡络合,随后通过大环的
氨基实现伪分子内催化。通过
1-十二醇的抑制效应和
2,4-二硝基氟苯对催化剂的修饰研究确认了这种对环
烷烃对疏
水性底物的有效结合能力。催化剂的游离胺形式作为有效的亲核试剂,生成了酰基化的
氨基对环
烷烃,这在产物分析中得到了证实。另一方面,质子化的胺形式也增强了酯的降解,保持了周转行为。基于动力学溶剂同位素效应和[10-氧[20]对环
烷烃-22(23)-基甲基]三
甲基氯铵在中性pH区域酯降解中的极小动力学效应,讨论了一个可行的反应机制。