咪唑衍生物的过渡金属配合物催化对硝基苯酚吡啶甲酸酯水解动力学研究

Hydrolysis of p-Nitrophenyl picolinate catalyzed by metal complexes containing imidazole groups in micellar solution

25 0±0 01℃时,研究了带有咪唑基团的配体与二价过渡金属离子生成的配合物在三种不同的表面活性剂(CTAB,Brij35和LSS)中催化对硝基苯酚吡啶甲酸酯(PNPP)水解的动力学。运用金属胶束催化的三元复合物动力学模型对所得的实验结果进行定量处理,得到了相关的动力学和热力学参数。结果表明:pH7 00时,在任何一种配合物与不同的表面活性剂生成的金属胶束溶液中,PNPP的水解速率都有较大的增加,尤其是铜(Ⅱ)配合物与两性离子表面活性剂(LSS)以及非离子表面活性剂生成的金属胶束对PNPP的水解反应表现出较高的催化活性,而在阳离子表面活性剂中,配合物催化PNPP水解反应的效率却并不高,这可能归因于阳离子表面活性剂带正电的极性头与金属离子之间的静电相斥作用;在所研究的三种配合物中,尽管Cu(Ⅱ)配合物具有最低的pKa值,但是在弱碱性条件下,Zn(Ⅱ)配合物却表现出更高的催化活性,这可能与催化剂在胶束溶液中的离子化状态以及不同配合物中活性物种的不同亲核能力有关。

The hydrolysis of pnitrophenyl picolinate(PNPP)catalyzed by Zn(Ⅱ),Cu(Ⅱ)and Co(Ⅱ)complexes of imidazole groups were investigated kinetically in the pH range 60～80 at the presence of three kinds of surfactants at different pH values and 250±001°C,respectively.The results indicated that Zn(Ⅱ)complex exhibited a great catalytic function in micellar solution with higher pH value,but when reactions were performed in weak acid solutions,Cu(Ⅱ)complex catalyzed the hydrolysis of PNPP more efficiently than Zn(Ⅱ)and Co(Ⅱ)complexes did,which may be attributable to the different ionization states of corresponding complexes in micellar media with different pH values and the different nucleophilic ability of active species in different complexes.In addition,complexes were more reactive in zwitterionic(LSS)and nonionic(Brij35)micelles than that in cationic(CTAB)micelle,which can be explained by the electrostatic interaction between metal ions of complexes and the head groups of micelles.The relative kinetic and thermodynamic parameters were obtained by kinetic analysis employing ternary complex model for metallomicellar catalysis.