Changing Mechanisms in the β-Cyclodextrin-Mediated Hydrolysis of Phenyl Esters of Perfluoroalkanoic Acids
作者:Mariana A. Fernández、Rita H. de Rossi
DOI:10.1021/jo034402b
日期:2003.9.1
The rate of hydrolysis of esters CF(3)(CF(2))(n)COOPh (1 (n = 1), 2 (n = 2), and 3 (n = 6)) was measured at pH 6.00 and at pH higher than 9.00 in the presence of beta-cyclodextrin (beta-CD). For compounds 1 and 2 the reaction rate decreases as the beta-CD concentration increases, and they show saturation effects at all pH. It is suggested that the substrate forms an inclusion complex with cyclodextrin
在pH 6.00和pH值为6的条件下测量酯CF(3)(CF(2))(n)COOPh(1(n = 1),2(n = 2)和3(n = 6))的水解速率。在存在β-环糊精(β-CD)的情况下,pH值高于9.00。对于化合物1和2,反应速率随β-CD浓度的增加而降低,并且它们在所有pH值下均表现出饱和作用。建议底物与环糊精形成包合物。速率数据的分析允许计算缔合平衡常数K(CD),所含化合物反应的速率常数k(c)和K(TS),它是过渡态假设的缔合平衡常数环糊精介导的反应。log K(CD)和log K(TS)与链中原子数的相关性不同。我们建议1和2的反应与空腔中包含的全氟烷基链发生,而三氟乙酸苯酯反应的过渡态涉及与空腔内部的芳基环形成复合物。在低pH下,抑制作用来自羰基对水的亲核攻击的保护。在碱性pH中,HO(-)作为外部亲核试剂的反应也受到抑制。由于底物在复合物中的不利取向,环糊精介导的反应在环