磷钼钒杂多酸在苯直接羟化反应中的催化作用——O2活化机理的探讨

磷钼钒杂多酸在有供电子体存在下具有活化氧和使苯直接羟化的催化性能。以抗坏血酸和亚硫酸钠为还原剂的实验表明不同的还原体系吸氧动力学和羟化活性不同。根据氧化还原滴定、循环伏安法、电解还原羟化反应以及光谱实验等测定结果, 对这两个不同体系提出了各自可能的氧的活化机理。认为在以抗坏血酸为还原剂的情况下, 杂多酸阴离子通过三电子传递过程直接络合氧, 氧与阴离子形成中间络合物为控制步骤。在以亚硫酸钠为还原剂的情况下, 供电子体可能先与阴离子络合活化, 直接参与氧的活化过程, 供电子体与阴离子的还原络合为控制步骤。

CATALYTIC ACTION OF MOLYBDOVANADOPHORIC ACID IN DIRECT HYDROXYLATION OF BENZENE——AN EXAMINATION OF O2 ACTIVATION

In the presence of electron donor, molybdovanadophosphoricacid (H_(3+n)PMo_(12-n) V_nO_(40)) are proved to possess catalytic activities in oxygen activation and benzene hydroxylation. O_2 absorption kinetics and hydroxylation activity are different for the two reducing agents used in this paper—ascorbic acid and sodium sulfite. Based on the results obtained from potentiometric titration, cyclic voltammogram measurement, electrolytic reduction hydroxylation and UV, ESR spectrum, plausible mechanisms of O_2 activation for both reducing systems could be drawn. Being reduced by ascorbic acid, the anion of heteropoly acid might directly coordinate to O_2 by transfering 3 electrons to it. The control step may be the coordination of O_2 to reduced anion. But in sodium sultite medium, the electron donor might directly take part in the process of O_2 activation forming a precursor complex with the anion. The reducing coordination of electron donor with anion could be regarded as the control step in this system.