铬(III)离子催化铈(IV)离子氧化四氢糠醇的反应动力学及机理

在酸性介质中用氧化还原滴定法研究了铈(IV)离子在铬(III)离子催化作用下, 于25～40 ℃区间氧化四氢糠醇的反应动力学. 结果表明反应对铈(IV)和四氢糠醇均为一级. 准一级速率常数k_obs随催化剂Cr(III)]增加而增大, 亦随H^＋]增加而增大, 而随增加而减小. 在氮气保护下, 反应不能引发丙烯酰胺聚合, 说明在反应中没有自由基产生. 提出了催化剂、底物和氧化剂间生成双核加合物的反应机理. 通过k_obs与的依赖关系, 并结合Ce(IV)在溶液中的平衡, 找到了本反应体系的动力学活性物种是Ce(SO₄)₂. 还计算出一些速率常数及相应的活化参数.

Kinetics and Mechanism of Chromium(III) Catalyzed Oxidation of Tetrahydrofurfuryl Alcohol by Cerium(IV) in Aqueous Sulphuric Acid Medium

The kinetics of chromium(III) catalyzed oxidation of tetrahydrofurfuryl alcohol by cerium(IV) in aqueous sulphuric acid medium was studied by titrimetric techniques in the temperature range of 25～40 ℃. The order was found to be unity with respect to both Ce(IV) and tetrahydrofurfuryl alcohol. It was found that the pseudo first order (THFA]>>Ce(IV)]) rate constants k_obs increased with increase of Cr(III)] and H^＋], but decreased with increase of . Under the protection of nitrogen the reaction system did not induce polymerization of acrylamide, indicating that no free radicals were generated. Formation of a dinuclear complex involving the oxidant, catalyst and the substrate has been proposed in the reaction mechanism. From the hydrogensulphate dependence, Ce(SO₄)₂ has been found as the kinetically active species. Some rate constants together with the activation parameters were evaluated.