Zhang Jin, Li Gui-Bai, Jun M A
School of Environmental Science and Engineering, Dalian Maritime University, Dalian 116012, China.
J Environ Sci (China). 2003 May;15(3):342-5.
Chlorine content and position of chlorinated phenols have many significant effects on the reactivity of oxido-reduction. The effects of chlorine content and position of chlorinated phenols on their oxidation kinetics by potassium permanganate were evaluated through different kinetics studies. Since chlorine was an electron withdrawing atom, the substitution of chlorine on the aromatic ring decreased the oxidation rate constant by sigma-electron withdrawing conductive effect. The substitution of chlorine at ortho or para position on the aromatic ring increased the oxidation rate constant by pi-electron donating conjugative effect, and the conjugative effect could counteract the negative impact of the conductive effect to some extent. On the other hand, the substitution of chlorine at ortho position on the aromatic ring decreased the oxidation rate constant by steric hindrance effect. The oxidation rate constants of phenol and chlorinated phenol studied decreased as follow order: 4-chlorophenol > 2,4-dichlorophenol > phenol > 2,6-dichlorophenol.
氯酚的氯含量和氯取代位置对氧化还原反应活性有诸多显著影响。通过不同的动力学研究评估了氯酚的氯含量和氯取代位置对其与高锰酸钾氧化反应动力学的影响。由于氯是吸电子原子，芳环上氯的取代通过σ-吸电子传导效应降低了氧化速率常数。芳环上邻位或对位氯的取代通过π-给电子共轭效应提高了氧化速率常数，且共轭效应在一定程度上可抵消传导效应的负面影响。另一方面，芳环上邻位氯的取代因空间位阻效应降低了氧化速率常数。所研究的苯酚和氯酚的氧化速率常数按以下顺序降低：4-氯酚＞2,4-二氯酚＞苯酚＞2,6-二氯酚。
